Polarizing plate and image display device

Abstract

To provide a polarizing plate which suppresses occurrence of polyene.SOLUTION: A polarizing plate 30 includes a polarizer 31 in which a dichroic dye is adsorbed and oriented to a polyvinyl alcohol-based resin film. The polarizing plate 30 includes a first protective film 33 laminated on one surface of the polarizer 31, and a second protective film 34 laminated on the other surface of the polarizer 31. A kurtosis (Rku) of the surface in the polarizer 31 is 3.0 or less.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a polarizing plate and an image display device. [Background technology]

[0002] As disclosed in Patent Document 1, it is known that in an image display device in which a front transparent member, a polarizing plate having a polarizer, and an image display cell are laminated in this order, polyenization occurs in the polyvinyl alcohol resin that constitutes the polarizer in a high-temperature environment. Note that Patent Document 1 describes the polarizer as a polarizing film.

[0003] Patent Document 1 describes that in the image display device described above, the moisture content of the pressure-sensitive adhesive layer or adhesive layer in contact with the polarizing plate is reduced in order to suppress polyenization, and also describes that the moisture content of the polarizer is reduced in order to suppress polyenization. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-179604 Summary of the Invention [Problem to be solved by the invention]

[0005] There is a demand for polarizing plates and image displays that are less susceptible to polyenization. [Means for solving the problem]

[0006] The present invention includes the following inventions. [1] a polarizer in which a dichroic dye is adsorbed and oriented in a polyvinyl alcohol-based resin film, a first protective film laminated on one surface of the polarizer, and a second protective film laminated on the other surface of the polarizer; The polarizing plate has a surface kurtosis (Rku) of 3.0 or less in the polarizer.

[0007] [2] The polarizing plate according to [1], wherein the kurtosis (Rku) is 2.0 or more and 3.0 or less. [3] The polarizing plate according to [1] or [2], wherein the polarizer and the first protective film, and the polarizer and the second protective film are laminated via an adhesive layer containing at least one urea compound selected from the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives.

[0008] [4] The polarizing plate according to any one of [1] to [3], wherein the polarizer has a thickness of 20 μm or less.

[0009] [5] The polarizing plate is applied to an image display device in which a transparent member, the polarizing plate, and an image display cell are laminated in this order, the surface on the second protective film side is the surface to be attached to the image display cell, The moisture permeability of the second protective film is 150 g / (m 2 The polarizing plate according to any one of [1] to [4], wherein the temperature is 24 hours or less.

[0010] [6] An image display device in which a transparent member is bonded to the first protective film of the polarizing plate described in any one of [1] to [5] via an adhesive layer, and an image display cell is bonded to the second protective film of the polarizing plate via an adhesive layer. [Effects of the Invention]

[0011] It is possible to provide a polarizing plate and an image display device in which polyenization is unlikely to occur in view of the surface shape of the polarizer. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an image display device equipped with a polarizing plate. [Figure 2] FIG. 2 is a schematic cross-sectional view showing a polarizing plate. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of a polarizing plate and an image display device including the polarizing plate will be described. <Image display device> FIG. 1 shows an example of an image display device 10 equipped with a polarizing plate 30. As shown in FIG.

[0014] The image display device 10 includes, for example, a transparent member 70, a first adhesive layer 41, a polarizing plate 30, a second adhesive layer 42, and an image display cell 60 laminated in this order. The first adhesive layer 41 is an adhesive layer that is in direct contact with the transparent member 70 and the polarizing plate 30. That is, the transparent member 70 is laminated on one surface of the polarizing plate 30 via the adhesive layer. Specifically, a first protective film 33 of the polarizing plate 30, which will be described later, is attached to the transparent member 70.

[0015] The second adhesive layer 42 is an adhesive layer that is in direct contact with the polarizing plate 30 and the image display cell 60. That is, the image display cell 60 is laminated on the other surface of the polarizing plate 30 via the adhesive layer. Specifically, a second protective film 34 of the polarizing plate 30, which will be described later, is attached to the image display cell 60.

[0016] Hereinafter, in the image display device 10, the side closer to the image display cell 60 is referred to as the cell side, and the side closer to the transparent member 70 is referred to as the viewing side. The image display device 10 can be used in, for example, televisions, personal computers, mobile devices such as mobile phones and tablet terminals, and in-vehicle applications, etc. Specific examples of in-vehicle applications include car navigation devices, speedometers, touch panels for air conditioners, back monitors, and rear monitors.

[0017] <Transparent materials> Examples of the transparent member 70 include a front transparent plate (window layer) and a touch panel. A transparent plate having appropriate mechanical strength and thickness is used as the front transparent plate. Examples of such transparent plates include transparent resin plates such as acrylic resins and polycarbonate resins, and glass plates. Examples of touch panels that can be used include various types of touch panels, such as resistive, capacitive, optical, and ultrasonic touch panels, as well as glass or transparent resin plates equipped with touch sensor functions.

[0018] <Image display cell> The image display cell 60 is not particularly limited, and examples thereof include a liquid crystal display panel, an organic electroluminescence (organic EL) display panel, an inorganic electroluminescence (inorganic EL) display panel, a plasma display panel, and a field emission display panel.

[0019] <First adhesive layer> The adhesive forming the first adhesive layer 41 can be any of various adhesives that can be used in image display devices, including, for example, rubber-based adhesives, acrylic-based adhesives, silicone-based adhesives, urethane-based adhesives, vinyl alkyl ether-based adhesives, polyvinyl alcohol-based adhesives, polyvinyl pollidone-based adhesives, polyacrylamide-based adhesives, and cellulose-based adhesives. Among these, acrylic-based adhesives are preferred. The acrylic-based adhesives contain an acrylic polymer as a base polymer, and examples thereof include the acrylic-based adhesives described in JP 2017-75998 A and the like.

[0020] The acrylic polymer in the acrylic pressure-sensitive adhesive has a main skeleton of a (meth)acrylic acid alkyl ester monomer unit. A (meth)acrylic acid alkyl ester having an alkyl group containing 1 to 20 carbon atoms is preferably used as the (meth)acrylic acid alkyl ester. The content of the (meth)acrylic acid alkyl ester is preferably 40% by mass or more, more preferably 60% by mass or more, based on the total amount of monomer components constituting the base polymer. Furthermore, from the viewpoint of adjusting the adhesive properties of the pressure-sensitive adhesive, a monomer unit such as a nitrogen-containing monomer unit or a hydroxyl group-containing monomer may be contained. Furthermore, a crosslinking agent may be used to form a crosslinked structure in the pressure-sensitive adhesive layer. Examples of the crosslinking agent include commonly used isocyanate-based crosslinking agents, epoxy-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, carbodiimide-based crosslinking agents, and metal chelate-based crosslinking agents. The amount of crosslinking agent used is typically 10 parts by mass or less, preferably 5 parts by mass or less, based on 100 parts by mass of the base polymer.

[0021] To the pressure-sensitive adhesive, tackifiers such as silane coupling agents, terpene-based tackifiers, styrene-based tackifiers, phenol-based tackifiers, rosin-based tackifiers, and epoxy-based tackifiers may be added in order to adjust the adhesive strength. Furthermore, to improve light resistance, ultraviolet absorbers may be added. In addition to the components exemplified above, the pressure-sensitive adhesive may contain additives such as plasticizers, softeners, antidegradants, fillers, colorants, antioxidants, surfactants, and antistatic agents, provided that the properties of the pressure-sensitive adhesive are not impaired.

[0022] Examples of methods for forming the adhesive layer include a method in which the adhesive is applied to a release-treated separator or the like, dried to form an adhesive layer, and then transferred to a polarizing plate or the like, or a method in which the adhesive is applied to a polarizing plate or the like, and dried to form an adhesive layer.

[0023] <Second adhesive layer> The adhesive forming second adhesive layer 42 can be appropriately selected from the various adhesives described above, as with first adhesive layer 41. Second adhesive layer 42 may use an adhesive of a different type from that of first adhesive layer 41, or may use an adhesive of the same type as that of first adhesive layer 41. There are no particular limitations on the thickness of second adhesive layer 42, and it is, for example, about 1 to 100 μm, and preferably about 2 to 50 μm.

[0024] <Polarizing plate> The polarizing plate 30 includes a polarizer 31 . 2, polarizing plate 30 has a first protective film 33 laminated on one surface of polarizer 31 via an adhesive layer 32. Polarizing plate 30 has a second protective film 34 laminated on the other surface of polarizer 31 via an adhesive layer 32.

[0025] <Polarizer> The polarizer is a uniaxially stretched polyvinyl alcohol (PVA) resin film to which a dichroic dye is adsorbed and aligned. The polyvinyl alcohol resin may be, for example, a saponified polyvinyl acetate resin. The saponification degree of the polyvinyl acetate resin is preferably 85 mol% or more, more preferably 90 mol% or more, and even more preferably 99 mol% or more.

[0026] Examples of polyvinyl acetate resins that can be used include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate with other copolymerizable monomers. Examples of the copolymerizable other monomers include unsaturated carboxylic acids, olefins, vinyl ethers, and unsaturated sulfonic acids.

[0027] The degree of polymerization of the polyvinyl alcohol resin is preferably 1,000 or more and 10,000 or less, and more preferably 1,500 or more and 5,000 or less. The polyvinyl alcohol resin may be modified. Examples of the modified polyvinyl alcohol resin include polyvinyl formal, polyvinyl acetal, and polyvinyl butyral modified with aldehydes.

[0028] Examples of the dichroic dye include iodine and water-soluble dichroic dyes. The thickness of the polarizer is not particularly limited, but is, for example, 1 μm or more, preferably 5 μm or more, more preferably 8 μm or more, and even more preferably 11 μm or more, and is 50 μm or less, preferably 30 μm or less, and more preferably 20 μm or less.

[0029] The polarizer preferably has a boron content of 0.5% by mass or more, more preferably 1.5% by mass or more, even more preferably 2.5% by mass or more, and may even have a boron content of 3.5% by mass or more. The boron content of the polarizer is preferably 5.5% by mass or less, more preferably 5.0% by mass or less, and even more preferably 4.5% by mass or less. By having a boron content of 4.5% by mass or less, shrinkage of the polarizer caused by heating can be suppressed.

[0030] [Urea compound] The polarizer may contain a urea compound. For example, the urea compound can be incorporated into the polarizer during the manufacturing process of the polarizer. Examples of methods for incorporating the urea compound into the polarizer include immersing the PVA-based resin layer in a treatment solvent containing the urea compound, or spraying, flowing, or dropping the treatment solvent onto the PVA-based resin layer. The step of immersing the PVA-based resin layer in a treatment solvent containing the urea compound may be performed simultaneously with or separately from steps such as swelling, stretching, dyeing, crosslinking, and washing in the method for manufacturing a polarizer described below. The urea compound contained in the polarizer may be a urea compound that is partly migrated from the adhesive layer described below to the polarizer.

[0031] The urea compound is at least one selected from the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives. The urea compounds can be used alone or in combination of two or more.

[0032] (urea derivative) A urea derivative is a compound in which at least one of the four hydrogen atoms of a urea molecule is substituted with a substituent. In this case, the substituent is not particularly limited, but is preferably a substituent consisting of carbon, hydrogen, and oxygen atoms.

[0033] Specific examples of the urea derivatives include mono-substituted ureas such as methylurea, ethylurea, propylurea, butylurea, isobutylurea, N-octadecylurea, 2-hydroxyethylurea, hydroxyurea, acetylurea, allylurea, 2-propynylurea, cyclohexylurea, phenylurea, 3-hydroxyphenylurea, (4-methoxyphenyl)urea, benzylurea, benzoylurea, o-tolylurea, and p-tolylurea.

[0034] Examples of disubstituted ureas include 1,1-dimethylurea, 1,3-dimethylurea, 1,1-diethylurea, 1,3-diethylurea, 1,3-bis(hydroxymethyl)urea, 1,3-tert-butylurea, 1,3-dicyclohexylurea, 1,3-diphenylurea, 1,3-bis(4-methoxyphenyl)urea, 1-acetyl-3-methylurea, 2-imidazolidinone (ethyleneurea), and tetrahydro-2-pyrimidinone (propyleneurea).

[0035] Examples of 4-substituted ureas include tetramethylurea, 1,1,3,3-tetraethylurea, 1,1,3,3-tetrabutylurea, 1,3-dimethoxy-1,3-dimethylurea, 1,3-dimethyl-2-imidazolidinone, and 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone.

[0036] (thiourea derivatives) A thiourea derivative is a compound in which at least one of the four hydrogen atoms of a thiourea molecule is substituted with a substituent. In this case, the substituent is not particularly limited, but is preferably a substituent consisting of a carbon atom, a hydrogen atom, and an oxygen atom.

[0037] Specific examples of the thiourea derivatives include mono-substituted thioureas such as N-methylthiourea, ethylthiourea, propylthiourea, isopropylthiourea, 1-butylthiourea, cyclohexylthiourea, N-acetylthiourea, N-allylthiourea, (2-methoxyethyl)thiourea, N-phenylthiourea, (4-methoxyphenyl)thiourea, N-(2-methoxyphenyl)thiourea, N-(1-naphthyl)thiourea, (2-pyridyl)thiourea, o-tolylthiourea, and p-tolylthiourea.

[0038] Examples of disubstituted thioureas include 1,1-dimethylthiourea, 1,3-dimethylthiourea, 1,1-diethylthiourea, 1,3-diethylthiourea, 1,3-dibutylthiourea, 1,3-diisopropylthiourea, 1,3-dicyclohexylthiourea, N,N-diphenylthiourea, N,N′-diphenylthiourea, 1,3-di(o-tolyl)thiourea, 1,3-di(p-tolyl)thiourea, 1-benzyl-3-phenylthiourea, 1-methyl-3-phenylthiourea, N-allyl-N′-(2-hydroxyethyl)thiourea, and ethylenethiourea.

[0039] Tri-substituted thioureas include trimethylthiourea. Examples of 4-substituted thioureas include tetramethylthiourea and 1,1,3,3-tetraethylthiourea.

[0040] [Surface shape of polarizer] The polarizer included in the polarizing plate has a surface kurtosis (Rku) of 3.0 or less. The surface kurtosis (Rku) of the polarizer is preferably 2.0 or more and 3.0 or less.

[0041] It is sufficient that the kurtosis (Rku) of at least one surface of the polarizer is within the above range, for example, that the kurtosis (Rku) of the surface on the viewing side of the polarizer is within the above range. The kurtosis (Rku) of both surfaces of the polarizer may be within the above range. Note that the kurtosis (Rku) of both surfaces of the polarizer usually have values ​​close to each other.

[0042] The measurement method for kurtosis (Rku) is specified in JIS B 0601:2013. Kurtosis (Rku) refers to kurtosis, a measure of surface sharpness, and indicates the peakedness (sharpness) of the height distribution. A kurtosis (Rku) value of 3.0 indicates a normal distribution, a value greater than 3.0 indicates a peaked height distribution, and a value less than 3.0 indicates that the height distribution of the surface irregularities is flattened.

[0043] Kurtosis (Rku) is calculated by the following formula: In the formula, Rq represents the root mean square roughness, and l represents the reference length. That is, kurtosis (Rku) is the fourth-power mean value of Z(x) over a reference length that has been made dimensionless by the fourth power of Rq (root mean square roughness) of the roughness curve, and is strongly influenced by protruding peaks or valleys of the surface irregularities.

[0044]

number

[0045] In a polarizing plate including a polarizer having a surface kurtosis (Rku) within the above range, polyenization of the PVA resin is unlikely to occur in a high-temperature environment. The surface kurtosis (Rku) of the polarizer can be adjusted, for example, by adjusting the amount of water contained in the polarizer and the adhesive composition when producing the polarizing plate.

[0046] On the surface of a polarizing plate where a polarizer and a protective film are laminated, streak-like irregularities (hereinafter also referred to as record streaks) may occur, as disclosed in, for example, JP 2010-117721 A. In a polarizing plate where the kurtosis (Rku) of the polarizer surface is less than 2.0, the record streaks that occur on the surface of the polarizing plate may become more noticeable visually. From this perspective, a polarizer with a kurtosis (Rku) of 2.0 or more on the surface can make the record streaks that occur on the surface of the polarizing plate less noticeable.

[0047] [Method for manufacturing polarizer] A known method can be used to manufacture a polarizer. For example, this manufacturing method involves sequentially performing a swelling step, a dyeing step, a crosslinking step, a washing step, and a drying step using a polyvinyl alcohol-based resin film as a raw film. The swelling step is a treatment step in which the raw film is immersed in a swelling liquid to swell it. The dyeing step is a treatment step in which the film after the swelling step is immersed in a dyeing liquid containing a dichroic dye to adsorb and align the dichroic dye in the film. The crosslinking step is a treatment step in which a crosslinking treatment is performed by bringing the film into contact with a crosslinking liquid. Between each step, i.e., before, after, or during any one or more of the treatment steps, a uniaxial stretching treatment can be performed as a stretching step.

[0048] The crosslinking step is a treatment step carried out for the purposes of imparting water resistance through crosslinking, adjusting hue (complementary color), etc. The crosslinking treatment may be carried out multiple times. When the crosslinking treatment is carried out multiple times, the crosslinking treatment for the purpose of imparting water resistance through crosslinking may be carried out multiple times, or the crosslinking treatment for the purpose of adjusting hue may be carried out multiple times. However, it is preferable to carry out the crosslinking treatment for the purpose of imparting water resistance through crosslinking at least once and the crosslinking treatment for the purpose of adjusting hue at least once, and it is more preferable to carry out the crosslinking step for the purpose of imparting water resistance through crosslinking after the crosslinking step for the purpose of adjusting hue.

[0049] The drying process can be carried out using a hot air dryer or a far-infrared heater. The drying temperature is, for example, 30°C to 100°C, preferably 30°C to 80°C, and more preferably 30°C to 50°C. The drying time is usually about 60 to 600 seconds, and preferably 120 to 600 seconds. A drying temperature of 50°C or less can easily prevent the kurtosis (Rku) of the surface of the polarizer from increasing in a polarizing plate produced using the polarizer. The drying process reduces the moisture content in the polarizer to a practical level. The moisture content is usually about 5 to 20% by mass, preferably 8 to 15% by mass, relative to the total mass of the polarizer. A moisture content of 5% by mass or more provides sufficient flexibility to prevent damage or breakage after drying. A moisture content of 20% by mass or less provides sufficient thermal stability.

[0050] <Protective film> The protective film is not particularly limited, and various transparent protective films that can be used in polarizing plates can be employed. Examples of materials that can be used to form the protective film include thermoplastic resins that are excellent in transparency, mechanical strength, thermal stability, moisture barrier properties, and isotropy. Examples of the thermoplastic resins include cellulose ester resins such as triacetyl cellulose, polyester resins such as polyethylene terephthalate and polyethylene naphthalate, polyethersulfone resins, polysulfone resins, polycarbonate resins, polyamide resins such as nylon and aromatic polyamide, polyimide resins, polyolefin resins such as polyethylene, polypropylene, and ethylene-propylene copolymers, (meth)acrylic resins, cyclic polyolefin resins (norbornene resins) having a cyclo- or norbornene structure, polyarylate resins, polystyrene resins, polyvinyl alcohol resins, and mixtures thereof. The protective film can also be a cured layer formed from a thermosetting resin or ultraviolet-curable resin, such as a (meth)acrylic, urethane, acrylic urethane, epoxy, or silicone resin. Among these, cellulose ester resins, polycarbonate resins, (meth)acrylic resins, cyclic polyolefin resins, and polyester resins are preferred.

[0051] The surface of the protective film to which the polarizer is not attached may be provided with a functional layer such as a hard coat layer, an antireflection layer, an antisticking layer, a diffusion layer, an antiglare layer, etc. The functional layer such as the hard coat layer, the antireflection layer, the antisticking layer, the diffusion layer, or the antiglare layer may be provided in the protective film itself, or may be provided separately as a layer separate from the protective film.

[0052] Either or both of the surface of the protective film to which the polarizer is attached and the surface of the polarizer to which the protective film is attached may be subjected to a surface treatment, such as a corona treatment, a plasma treatment, a primer treatment, or a saponification treatment.

[0053] The moisture permeability of the protective film is not particularly limited. For example, the second protective film 34 of the protective films has a moisture permeability of 350 g / (m) in an environment of a temperature of 40° C. and a relative humidity of 90%. 2 24 hours) or less, preferably 150 g / (m 2 The moisture permeability is, for example, 50 g / (m 2 The moisture permeability is 50g / (m 2 ·24 hours) or more 350g / (m 2 24 hours) or less, and 80g / (m 2 ·24 hours) or more 300g / (m 2 24 hours) or less is more preferable, and 100g / (m 2 ·24 hours) or more 150g / (m 2 The moisture permeability can be measured in accordance with the moisture permeability test (cup method) of JIS Z0208.

[0054] <Adhesive layer> The adhesive composition constituting the adhesive layer 32 is preferably a water-based adhesive composition containing a resin. The water-based adhesive composition is an adhesive composition consisting of an aqueous solution in which adhesive components are dissolved in water, and the solids concentration of the water-based adhesive composition is preferably 0.5 to 20 mass %, more preferably 1 to 15 mass %.

[0055] Examples of resins contained in the aqueous adhesive composition (or adhesive layer) include urethane resins and polyvinyl alcohol (PVA) resins, with PVA resins being preferred. When a polyvinyl alcohol resin is used as the main component of the aqueous adhesive composition, the polyvinyl alcohol resin may be a polyvinyl alcohol resin such as a partially saponified polyvinyl alcohol or a fully saponified polyvinyl alcohol, or a modified polyvinyl alcohol resin. Examples of the modified polyvinyl alcohol resin include a carboxyl group-modified polyvinyl alcohol resin and an acetoacetyl group-modified polyvinyl alcohol resin.

[0056] The average degree of polymerization of the polyvinyl alcohol resin (preferably an acetoacetyl group-modified polyvinyl alcohol resin) is preferably from 100 to 5500, more preferably from 500 to 4500, from the viewpoint of adhesiveness.

[0057] The degree of saponification of the polyvinyl alcohol resin (preferably an acetoacetyl group-modified polyvinyl alcohol resin) is usually 80 mol % to 100 mol %, and preferably 85 mol % or more.

[0058] The degree of modification (amount of modification) with acetoacetyl groups in the acetoacetyl group-modified polyvinyl alcohol resin is usually 0.1 mol % to 40 mol %, and preferably 0.5 mol % to 20 mol %, from the viewpoint of adhesiveness.

[0059] Among aqueous adhesive compositions, polyvinyl alcohol-based adhesive compositions are preferred, and acetoacetyl-modified polyvinyl alcohol-based adhesive compositions are more preferred. That is, the adhesive layer 32 is preferably a cured layer of an aqueous adhesive composition containing a polyvinyl alcohol-based resin.

[0060] The adhesive may be applied to either the protective film side or the polarizer side, or to both. After lamination, a drying step is performed to form an adhesive layer consisting of a dried coated layer. After the drying step, ultraviolet light or electron beams may be irradiated as necessary.

[0061] The thickness of the adhesive layer 32 is not particularly limited, but is preferably, for example, about 1 to 5000 nm, more preferably about 10 to 1000 nm, and even more preferably about 10 to 300 nm.

[0062] The adhesive composition constituting the adhesive layer 32 may contain a urea compound. The adhesive composition constituting the adhesive layer 32 may contain a nitric acid compound. The urea compound, the nitric acid compound, and other components that may be contained in the adhesive composition will be described below.

[0063] [Urea compound] The urea compound is at least one selected from the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives. One urea compound can be used alone, or two or more can be used in combination. Specific examples of the urea compound can be appropriately selected from the urea compounds that may be contained in the polarizer. Urea compounds include water-soluble and slightly water-soluble urea compounds, and either type can be used. When a slightly water-soluble urea compound is used in a water-soluble adhesive, it is preferable to devise a dispersion method to prevent an increase in haze after forming the adhesive layer. Urea is preferred as the urea compound. When the adhesive composition contains a urea compound, it is easier to suppress polyenization of the PVA resin in a high-temperature environment.

[0064] The content of the urea compound in the adhesive composition (or adhesive layer) is preferably, for example, in the following range: For example, when the adhesive composition is an aqueous adhesive containing a polyvinyl alcohol-based resin, the content of the urea compound is 0.1 parts by mass or more and 400 parts by mass or less, preferably 1 part by mass or more and 200 parts by mass or less, and more preferably 3 parts by mass or more and 100 parts by mass or less, per 100 parts by mass of the polyvinyl alcohol-based resin.

[0065] [Nitrate compound] The nitric acid compound is not particularly limited, but is preferably a nitrate. Specific preferred examples of the nitrate include alkali metal nitrates such as lithium nitrate, potassium nitrate, and sodium nitrate, aluminum nitrate, zinc nitrate, copper(II) nitrate, and silver nitrate, with zinc nitrate being more preferred. The adhesive composition may contain one type of nitric acid compound alone or two or more types in combination.

[0066] The content of the nitric acid compound in the adhesive composition (or adhesive layer) is preferably, for example, in the following range: For example, when the adhesive composition is an aqueous adhesive containing a polyvinyl alcohol-based resin, the content of the nitric acid compound is 0.1 parts by mass or more and 600 parts by mass or less, preferably 1 part by mass or more and 400 parts by mass or less, and more preferably 3 parts by mass or more and 200 parts by mass or less, per 100 parts by mass of the polyvinyl alcohol-based resin.

[0067] When the adhesive composition (or adhesive layer) contains both a nitric acid compound and a urea compound, the mass ratio of the content of the nitric acid compound to the content of the urea compound (nitric acid compound / urea compound) is 1 or more and 6 or less, preferably 1 or more and 5 or less, and more preferably 2 or more and 5 or less.

[0068] As long as the mass ratio is within the above-mentioned specific range, the content of the nitric acid compound in the adhesive composition and the content of the urea compound in the adhesive composition can each be changed as appropriate.

[0069] [Other ingredients] The adhesive composition may contain an organic solvent. Alcohols are preferred as the organic solvent because they are miscible with water, and among alcohols, methanol or ethanol is more preferred. The concentration of the organic solvent in the aqueous adhesive is preferably 10% by mass or more and 70% by mass or less, more preferably 15% by mass or more and 60% by mass or less, and even more preferably 20% by mass or more and 60% by mass or less. Increasing the organic solvent content in the aqueous adhesive composition can reduce the water content. Having an organic solvent concentration of 10% by mass or more can more easily suppress polyenization of the PVA resin in a high-temperature environment. Furthermore, having an organic solvent content of 70% by mass or less can suppress deterioration of color. Some of the urea derivatives described above have low solubility in water, but sufficient solubility in alcohol. In this case, one preferred embodiment is to dissolve a urea compound in alcohol to prepare an alcohol solution of the urea compound, and then add the alcohol solution of the urea compound to the aqueous PVA solution to prepare the adhesive.

[0070] The aqueous adhesive composition may contain a crosslinking agent. The crosslinking agent is typically a compound having at least two functional groups per molecule that are reactive with the polymer or other components that make up the adhesive. Examples of such crosslinking agents include alkylenediamines, isocyanates, epoxies, aldehydes, amino-formaldehydes such as methylolmelamine, glyoxal, and glyoxal derivatives. The amount of crosslinking agent in the adhesive is typically about 5 to 60 parts by mass per 100 parts by mass of the polymer or other components that make up the adhesive.

[0071] The aqueous adhesive composition may contain a dicarboxylic acid such as maleic acid or phthalic acid to improve heat resistance. The content of the dicarboxylic acid is preferably 0.01 to 5 parts by mass, more preferably 0.02 to 1 part by mass, per 100 parts by mass of the PVA resin.

[0072] <Polarizing Plate Manufacturing Method> The method for producing a polarizing plate includes a laminating step and a post-laminating drying step. The laminating step is a step of laminating a protective film to a polarizer via an adhesive composition. The laminating step can be performed using, for example, a roll laminating machine. The polarizing plate may be manufactured by preparing long members, laminating the respective members together using a roll-to-roll process, and then cutting them into a predetermined shape, or by cutting the respective members into a predetermined shape and then laminating them together.

[0073] The post-lamination drying step is a step of obtaining a polarizing plate by drying a laminate obtained by the lamination step, which has a layer structure of "first protective film / adhesive composition (adhesive layer before drying) / polarizer / adhesive composition (adhesive layer before drying) / second protective film." The post-lamination drying step is not particularly limited, and can be performed using, for example, a hot air oven.

[0074] The post-lamination drying step preferably includes a first drying step and a second drying step performed subsequently to the first drying step. In the second drying step, drying is preferably performed at a temperature different from that in the first drying step. By performing the first drying step and the second drying step, it is easy to adjust the kurtosis (Rku) of the surface of the polarizer.

[0075] The drying temperature in the first drying step is not particularly limited as long as it is a temperature sufficient to reduce the moisture contained in the adhesive composition (adhesive layer), but is, for example, 30°C or higher and 120°C or lower, preferably 40°C or higher and 100°C or lower, and more preferably 45°C or higher and 80°C or lower.

[0076] The drying time in the first drying step is not particularly limited, but is, for example, from 1 minute to 10 minutes, preferably from 2 minutes to 8 minutes, and more preferably from 3 minutes to 6 minutes. The drying temperature in the second drying step is preferably set to a temperature higher than the drying temperature in the first drying step. By lowering the drying temperature in the first drying step, which is the initial step in the post-lamination drying step, it is possible to prevent the kurtosis (Rku) of the surface of the polarizer from increasing. The drying temperature in the second drying step is, for example, 50°C or higher and 120°C or lower, preferably 60°C or higher and 100°C or lower, and more preferably 65°C or higher and 80°C or lower.

[0077] The drying time in the second drying step is not particularly limited, but is, for example, 1 minute to 10 minutes, preferably 2 minutes to 8 minutes, and more preferably 3 minutes to 6 minutes. The drying time in the second drying step may be different from or the same as the drying time in the first drying step.

[0078] The total drying time in the first drying step and the second drying step is, for example, 2 minutes or more and 20 minutes or less, preferably 4 minutes or more and 16 minutes or less, and more preferably 6 minutes or more and 12 minutes or less.

[0079] In the post-lamination drying process, the second drying process following the first drying process means, for example, that the process is carried out in the following order: The laminate is placed in a hot air oven and dried at a first drying temperature (first drying process), and then, while the laminate remains in the hot air oven, it is dried at a second drying temperature (second drying process). It is preferable to carry out the first and second drying processes without any time gap between them, but a gap that may arise during the progress of the manufacturing process is acceptable. For example, between the end of the first drying process and the start of the second drying process, there may be a period during which the temperature is raised from the drying temperature in the first drying process to the drying temperature in the second drying process.

[0080] <Effects of this embodiment> Polarizing plates and image display devices have a problem in that yellowing occurs due to the progression of polyenization of the PVA resin constituting the polarizer in high-temperature environments. In this regard, a polarizing plate and image display device having a polarizer surface with a kurtosis (Rku) of 3.0 or less can suppress the polyenization of the PVA resin constituting the polarizer. Therefore, a polarizing plate that is less likely to undergo polyenization can be provided from the perspective of the surface shape of the polarizer, specifically, kurtosis (Rku).

[0081] When a film with low moisture permeability is used as the protective film of a polarizing plate, the kurtosis (Rku) of the surface of the polarizer tends to increase. In this regard, according to the manufacturing method of this embodiment, which can suppress the increase in kurtosis (Rku), the moisture permeability of the second protective film is set to 150 g / (m 2 Even if the temperature is lower than 24 hours, a polarizing plate having a surface kurtosis (Rku) of 3.0 or less can be manufactured.

[0082] When the thickness of a polarizer included in a polarizing plate is small, the kurtosis (Rku) of the surface of the polarizer tends to increase. In this regard, the manufacturing method of the present embodiment, which can suppress an increase in kurtosis (Rku), can manufacture a polarizing plate in which the kurtosis (Rku) of the surface of the polarizer is 3.0 or less, even when the thickness of the polarizer is 20 μm or less.

[0083] When the boron content of the polarizer included in a polarizing plate is high, the kurtosis (Rku) of the surface of the polarizer tends to increase. In this regard, the manufacturing method of the present embodiment, which can suppress an increase in kurtosis (Rku), can manufacture a polarizing plate in which the kurtosis (Rku) of the surface of the polarizer is 3.0 or less, even if the boron content of the polarizer is 4.20 mass% or more.

[0084] The polarizing plate and image display device, in which polyenization of the PVA resin is unlikely to occur even in a high-temperature environment, can be suitably used in applications where they are exposed to a high-temperature environment for a long period of time. For example, image display devices for in-vehicle applications such as car navigation systems and rearview monitors may be exposed to a high-temperature environment for a long period of time. The polarizing plate and image display device of this embodiment can also be suitably used in in-vehicle applications.

[0085] In this embodiment, "high temperature environment" means an environment of 100°C or higher, for example, 105°C or higher. Furthermore, "long period of time" means 100 hours or longer, for example, 500 hours. [Example]

[0086] The polarizing plate and the image display device will be described in more detail based on the following examples, but the polarizing plate and the image display device are not limited to the configurations described in the examples. <Measurement of moisture permeability of protective film> The moisture permeability of the protective film used in the production of the polarizing plate was measured at a temperature of 40° C. and a relative humidity of 90% in accordance with the moisture permeability test (cup method) of JIS Z0208.

[0087] <Calculation of single hue b value> The single transmittance was measured using a spectrophotometer / colorimeter (Konica Minolta, Inc., CM-3700A), and the single hue b value was determined by calculating the chromaticity in the L*a*b* (CIE) color system using the color matching function of Illuminant C for the single transmittance obtained.

[0088] (Production Example 1: Preparation of polarizer) (Preparation of Polarizer 1) A 30 μm-thick polyvinyl alcohol-based resin film was immersed in pure water at 21.5°C for 79 seconds (swelling step), then immersed in an aqueous solution at 23°C containing 1.0 mM iodine and having a potassium iodide / boric acid / water mass ratio of 2 / 2 / 100 for 151 seconds (dyeing step). Subsequently, the film was immersed in an aqueous solution at 68.5°C containing a potassium iodide / boric acid / water mass ratio of 2.5 / 4 / 100 for 76 seconds (first crosslinking step). Subsequently, the film was immersed in an aqueous solution at 45°C containing a potassium iodide / boric acid / zinc chloride / water mass ratio of 3 / 5.5 / 0.6 / 100 for 11 seconds (second crosslinking step, metal ion treatment step). The film was then immersed in a washing bath for cleaning (washing step) and dried at 46°C (drying step), yielding a 12 μm-thick polarizer in which iodine was adsorbed and aligned in the polyvinyl alcohol. The stretching was mainly performed in the dyeing step and the first crosslinking step, and the total stretching ratio was 5.85 times. The boron content was 4.27% by mass. The thickness of the obtained polarizer was measured using a digital micrometer "MH-15M" manufactured by Nikon Corporation. The boron content of the polarizer was measured using ICP-AES.

[0089] (Preparation of Polarizer 2) A 30 μm-thick polyvinyl alcohol-based resin film was immersed in pure water at 21.5°C for 79 seconds (swelling step), then immersed in an aqueous solution at 23°C containing 1.0 mM iodine and having a mass ratio of potassium iodide / boric acid / water of 2 / 2 / 100 for 151 seconds (dyeing step). Subsequently, the film was immersed in an aqueous solution at 68.5°C containing a mass ratio of potassium iodide / boric acid / water of 2.5 / 4 / 100 for 76 seconds (first crosslinking step). Subsequently, the film was immersed in an aqueous solution at 45°C containing a mass ratio of potassium iodide / boric acid / zinc chloride / water of 3 / 5.6 / 0.6 / 100 for 11 seconds (second crosslinking step, metal ion treatment step). The film was then immersed in a washing bath for cleaning (washing step) and dried at 53°C (drying step) to obtain a 12 μm-thick polarizer in which iodine was adsorbed and aligned in the polyvinyl alcohol. The stretching was mainly performed in the dyeing step and the first crosslinking step, and the total stretching ratio was 5.85 times. The boron content was 4.30% by mass. The thickness of the obtained polarizer was measured using a digital micrometer "MH-15M" manufactured by Nikon Corporation. The boron content of the polarizer was measured using ICP-AES.

[0090] (Fabrication of Polarizer 3) A 30 μm-thick polyvinyl alcohol resin film was immersed in pure water at 21.5°C for 79 seconds (swelling step), then immersed in an aqueous solution at 23°C containing 1.0 mM iodine and having a potassium iodide / boric acid / water mass ratio of 2 / 2 / 100 for 151 seconds (dyeing step). Subsequently, the film was immersed in an aqueous solution at 68.5°C containing a potassium iodide / boric acid / water mass ratio of 2.5 / 4 / 100 for 76 seconds (first crosslinking step). Subsequently, the film was immersed in an aqueous solution at 45°C containing a potassium iodide / boric acid / zinc chloride / water mass ratio of 3 / 5.7 / 0.6 / 100 for 11 seconds (second crosslinking step, metal ion treatment step). The film was then immersed in a washing bath for cleaning (washing step) and dried at 46°C (drying step) to obtain a 12 μm-thick polarizer in which iodine was adsorbed and aligned in the polyvinyl alcohol. The stretching was mainly performed in the dyeing step and the first crosslinking step, and the total stretching ratio was 5.85 times. The boron content was 4.33% by mass. The thickness of the obtained polarizer was measured using a digital micrometer "MH-15M" manufactured by Nikon Corporation. The boron content of the polarizer was measured using ICP-AES.

[0091] (Production Example 2: Preparation of adhesive composition) 50 g of modified polyvinyl alcohol resin having acetoacetyl groups (Gohsenex Z-410, manufactured by Mitsubishi Chemical Corporation) was dissolved in 950 g of pure water, heated at 90°C for 2 hours, and then cooled to room temperature to obtain an acetoacetyl group-modified polyvinyl alcohol resin solution.

[0092] Maleic acid, urea, a 40% by mass solution of glyoxal, methanol, and pure water were added to the obtained acetoacetyl group-modified polyvinyl alcohol resin solution in the amounts shown in Table 1 below to prepare adhesive compositions 1 and 2.

[0093] [Table 1]

[0094] <Preparation of polarizing plate> The following protective films were prepared: Protective film F1: saponified triacetyl cellulose film with a hard coat layer (manufactured by Toppan Printing Co., Ltd., product name "40FJCHCN-LMP", triacetyl cellulose film thickness: 40 μm, hard coat layer thickness: 7 μm). Moisture permeability is 200 g / (m 2 -24 hours). Protective film F2: Cycloolefin polymer film (Arton resin film manufactured by JSR Corporation, thickness 25 μm). Moisture permeability is 100 g / (m 2 -24 hours).

[0095] (Production Example 3: Preparation of polarizing plate) The following polarizing plates were prepared. The configuration of each polarizing plate is shown in Table 2. (Preparation of Polarizing Plate (1)) A protective film F1 was laminated on one surface of the polarizer 1 produced in Production Example 1 via the adhesive composition 1 prepared in Production Example 2. A protective film F2 was laminated on the other surface of the polarizer via the adhesive composition 1 prepared in Production Example 2, and the films were laminated using a roll laminator. The film was then dried at 50°C for 4 minutes (first drying step) and then further dried at 70°C for 4 minutes (second drying step) to obtain a polarizing plate (1). The adhesive layers made of the adhesive compositions each had a thickness of 80 nm after drying. The protective film F1 corresponds to the first protective film. The protective film F2 corresponds to the second protective film.

[0096] (Preparation of Polarizing Plate (2)) A protective film F1 was laminated on one surface of the polarizer 2 produced in Production Example 1 via the adhesive composition 1 prepared in Production Example 2. A protective film F2 was laminated on the other surface of the polarizer via the adhesive composition 1 prepared in Production Example 2, and the films were laminated using a roll laminator. The film was then dried at 50°C for 4 minutes (first drying step), and then further dried at 70°C for 4 minutes (second drying step) to obtain a polarizing plate (2). The adhesive layers made of the adhesive compositions each had a thickness of 80 nm after drying. The protective film F1 corresponds to the first protective film. The protective film F2 corresponds to the second protective film.

[0097] (Preparation of polarizing plate (3)) A protective film F1 was laminated on one surface of the polarizer 3 produced in Production Example 1 via the adhesive composition 2 prepared in Production Example 2. A protective film F2 was laminated on the other surface of the polarizer via the adhesive composition 2 prepared in Production Example 2, and the films were laminated using a roll laminator. The film was then dried at 50°C for 4 minutes (first drying step) and then further dried at 70°C for 4 minutes (second drying step) to obtain a polarizing plate (3). The adhesive layers made of the adhesive compositions each had a thickness of 80 nm after drying. The protective film F1 corresponds to the first protective film. The protective film F2 corresponds to the second protective film.

[0098] (Preparation of polarizing plate (4)) A protective film F1 was laminated on one surface of the polarizer 1 produced in Production Example 1 via the adhesive composition 1 prepared in Production Example 2. A protective film F2 was laminated on the other surface of the polarizer via the adhesive composition 1 prepared in Production Example 2, and the films were bonded using a roll laminator. The film was then dried at 70°C for 8 minutes to obtain a polarizing plate (4). The adhesive layers made of the adhesive compositions each had a thickness of 80 nm after drying. The protective film F1 corresponds to the first protective film. The protective film F2 corresponds to the second protective film.

[0099] (Evaluation of Kurtosis (Rku)) The prepared polarizing plates (1) to (4) were measured over an area of ​​11,193 μm × 11,201 μm using a Hitachi High-Technologies Corporation nano 3D optical interferometry system VS1800 with a 2.5x objective lens, a 0.5x lens barrel, a 530 White wavelength filter, and a Wave (piezo) measurement mode. After outputting using a fourth-order polynomial correction, the intermediate wavelengths between 250 nm and 700 nm were extracted, and the kurtosis (Rku) was calculated as a five-point average from the profile in the direction perpendicular to the absorption axis. The measurement was performed from the first protective film side of each polarizing plate. In other words, the kurtosis (Rku) of the surface on the viewing side of the polarizer was calculated.

[0100] As a result, the kurtosis (Rku) was 2.6 for polarizing plate (1), 2.8 for polarizing plate (2), 1.9 for polarizing plate (3), and 3.5 for polarizing plate (4).

[0101] [Table 2]

[0102] (Production Example 4: Preparation of laminate) (Preparation of laminate (1)) The second protective film side of polarizing plate (1), i.e., the protective film F2 side, was subjected to a 0.8 kW corona treatment, and then a 25 μm acrylic adhesive layer was formed to obtain polarizing plate (1) with an adhesive layer. The obtained polarizing plate (1) with an adhesive layer was cut to a size of 90 mm × 100 mm so that the absorption axis was parallel to the long side. A 100 mm × 100 mm alkali-free glass ("EAGLE XG" manufactured by Corning) was laminated to the adhesive layer surface of the cut polarizing plate (1) with an adhesive layer to obtain polarizing plate (1) with a glass plate. This alkali-free glass is a substitute for the image display cell in an image display device.

[0103] A first adhesive layer-attached resin film, which was composed of a 250 μm thick adhesive layer (3M's "CEF2810") and an 80 μm thick polyester resin film having a release layer, was attached to the first protective film side of the obtained polarizing plate with glass plate, i.e., the protective film F1 side, on the adhesive layer side to produce laminate (1).

[0104] (Preparation of laminate (2)) A laminate (2) was produced in the same manner as above, except that the polarizing plate (1) was changed to the polarizing plate (2).

[0105] (Preparation of laminate (3)) A laminate (3) was produced in the same manner as above, except that the polarizing plate (1) was changed to the polarizing plate (3).

[0106] (Preparation of laminate (4)) A laminate (4) was produced in the same manner as above, except that the polarizing plate (1) was changed to the polarizing plate (4).

[0107] (Example 1: Production of image display device (1)) The laminate (1) obtained in Production Example 4 was heated at 95° C. for 3 hours (heating step) to prepare an image display device (1) with a resin film.

[0108] [Preparation of evaluation sample (image display device)] The image display device (1) with the resin film obtained in Example 1 was left to stand for 1 hour in an environment of 23°C and 60% relative humidity. After standing, the 80 μm polyester resin film was peeled off, and alkali-free glass ("EAGLE XG" manufactured by Corning) was attached to the exposed 250 μm adhesive layer, and this was used as evaluation sample (1) (image display device (1)). Note that this evaluation sample is a laminate for evaluation in which alkali-free glass is laminated as a substitute for the image display cell in the image display device.

[0109] (Examples 2 and 3: Preparation of image display devices (2) and (3)) The laminate (2) and the laminate (3) were each heated at 95°C for 3 hours (heating step) to produce image display devices (2) and (3) with resin films. Evaluation samples were produced in the same manner as above, except that the image display device (1) with resin films was changed to the image display devices (2) and (3) with resin films.

[0110] (Comparative Example 1: Preparation of image display device (4)) The laminate (4) was heated at 95°C for 3 hours (heating step) to prepare an image display device (4) with a resin film. An evaluation sample was prepared in the same manner as above, except that the image display device (1) with a resin film was replaced with the image display device (4) with a resin film.

[0111] <High temperature durability evaluation> Each of the four evaluation samples of image display devices (1) to (4) was subjected to a temperature of 50°C and a pressure of 5 kgf / cm 2After autoclaving for 15 minutes at a pressure of 490.3 kPa, the samples were left to stand for 24 hours in an environment with a temperature of 23°C and a relative humidity of 50%. The b value of the individual hue of each evaluation sample was then measured (initial value). After measuring the transmittance of the evaluation sample, each evaluation sample was left to stand for 500 hours in an environment with a temperature of 105°C (high temperature durability test). The b value of the individual hue of each evaluation sample after standing was then measured.

[0112] The Δb value was calculated from the result of (single hue b value after high-temperature durability test) - (initial single hue b value). The results are shown in Table 2. From the viewpoint that the color of the polarizing plate becomes visually perceived as yellowish as polyenization progresses, a Δb value of 5 or less was evaluated as indicating that polyenization had been suppressed, and a Δb value of more than 5 was evaluated as indicating that polyenization had progressed.

[0113] The above results show that there is a correlation between the kurtosis (Rku) on the polarizer surface and the change in the b value of the single hue after the high-temperature durability test. In Examples 1 to 3, which used polarizing plates (1) to (3) with a kurtosis (Rku) of 3.0 or less, the Δb value was smaller than in Comparative Example 1, which used polarizing plate (4). In Examples 1 to 3, the Δb value was 5 or less, and the favorable result of suppressing polyenation was obtained. [Explanation of symbols]

[0114] 10...Image display device 30...Polarizing plate 31...Polarizer 32...Adhesive layer 33...First protective film 34...Second protective film 41...First adhesive layer 42…Second adhesive layer 60...Image display cell 70...Transparent material

Claims

1. a polarizer in which a dichroic dye is adsorbed and oriented in a polyvinyl alcohol-based resin film; a first protective film laminated on one surface of the polarizer; and a second protective film laminated on the other surface of the polarizer, The polarizing plate has a surface kurtosis (Rku) of 3.0 or less in the polarizer.

2. 2. The polarizing plate according to claim 1, wherein the kurtosis (Rku) is 2.0 or more and 3.0 or less.

3. 2. The polarizing plate according to claim 1, wherein the polarizer and the first protective film, and the polarizer and the second protective film are laminated via an adhesive layer containing at least one urea compound selected from the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives.

4. 2. The polarizing plate according to claim 1, wherein the polarizer has a thickness of 20 [mu]m or less.

5. The polarizing plate is applied to an image display device in which a transparent member, the polarizing plate, and an image display cell are laminated in this order, the surface on the second protective film side is the surface to be bonded to the image display cell, The moisture permeability of the second protective film is 150 g / (m ２ 2. The polarizing plate according to claim 1, wherein the temperature is 24 hours or less.

6. An image display device in which a transparent member is bonded to the first protective film of the polarizing plate described in any one of claims 1 to 5 via an adhesive layer, and an image display cell is bonded to the second protective film of the polarizing plate via an adhesive layer.

Images