JPWO2020138358A1 - Polarizing plate and polarizing plate roll - Google Patents

Abstract

A polarizing plate having excellent durability despite being extremely thin is provided. The polarizing plate of the present invention has a polarizer, a first protective layer arranged on one side of the polarizer, and a second protective layer arranged on the other side of the polarizer. The first protective layer is composed of a solidified coating film of an organic solvent solution of a thermoplastic acrylic resin, and the glass transition temperature of the first protective layer is 95 ° C. or higher. The second protective layer is made of a resin film. In one embodiment, the thickness of the first protective layer is 10 μm or less.

Description

The present invention relates to a polarizing plate and a polarizing plate roll.

In an image display device (for example, a liquid crystal display device or an organic EL display device), a polarizing plate is often arranged on at least one side of a display cell due to the image forming method. In recent years, image display devices have become thinner and more flexible, and along with this, there is a strong demand for thinner polarizing plates. However, the thinner the polarizing plate, the more remarkable the problem of durability that the optical characteristics in a heating and humidifying environment deteriorate.

JP-A-2015-210474

The present invention has been made to solve the above-mentioned conventional problems, and a main object thereof is to provide a polarizing plate having excellent durability in spite of being extremely thin.

The polarizing plate of the present invention has a polarizer, a first protective layer arranged on one side of the polarizer, and a second protective layer arranged on the other side of the polarizer. .. The first protective layer is composed of a solidified coating film of an organic solvent solution of a thermoplastic acrylic resin, and the glass transition temperature of the first protective layer is 95 ° C. or higher. The second protective layer is made of a resin film.
In one embodiment, the thickness of the first protective layer is 10 μm or less.
In one embodiment, the iodine adsorption amount of the first protective layer is 4.0% by weight or less.
In one embodiment, the thermoplastic acrylic resin has at least one selected from the group consisting of a lactone ring unit, a glutaric anhydride unit, a glutarimide unit, a maleic anhydride unit and a maleimide unit.
In one embodiment, the in-plane retardation Re (550) of the first protective layer is 0 nm to 10 nm, and the thickness direction retardation Rth (550) is −20 nm to +10 nm.
In one embodiment, the first protective layer is arranged on the display cell side of the image display device, and the second protective layer is arranged on the opposite side of the display cell. In one embodiment, the polarizing plate is arranged on the visual side of the image display device.
According to another aspect of the present invention, a polarizing plate roll is provided. This polarizing plate roll is formed by winding the above-mentioned polarizing plate into a roll shape.

According to the present invention, one of the protective layers arranged on both sides of the polarizing element is composed of a solidified coating film of an organic solvent solution of a thermoplastic acrylic resin, and the glass transition temperature thereof is set to a predetermined value or higher. As a result, a polarizing plate having excellent durability can be obtained even though it is very thin.

It is the schematic sectional drawing of the polarizing plate by one Embodiment of this invention. It is the schematic which shows an example of the drying shrinkage treatment using the heating roll in the manufacturing method of the polarizing plate by one Embodiment of this invention.

A. Schematic FIG. 1 is a schematic cross-sectional view of a polarizing plate according to one embodiment of the present invention. The polarizing plate 100 of the illustrated example includes a polarizer 10, a first protective layer 20 arranged on one side of the polarizer 10, and a second protective layer 30 arranged on the other side of the polarizer 10. And have. The thickness of the polarizer 10 is preferably 8 μm or less. When applied to an image display device, the polarizing plate 100 may be arranged on the viewing side of the display cell, or may be arranged on the side opposite to the viewing side (back side). In either case, the first protective layer 20 may be arranged on the display cell side or on the opposite side (outside) of the display cell. In one embodiment, the polarizing plate 100 is arranged on the visual side of the display cell (as a result, the image display device), and the first protective layer 20 is arranged on the display cell side. By arranging the first protective layer 20 on the display cell side, it is possible to realize a polarizing plate having both excellent optical characteristics and excellent durability.

The polarizing plate may be long or single-wafered. When the polarizing plate has a long shape, it is preferably wound into a roll to form a polarizing plate roll.

Typically, the polarizing plate has an adhesive layer as the outermost layer on one side (typically, the display cell side), and can be attached to the display cell. If necessary, a surface protective film and / or a carrier film may be temporarily attached to the polarizing plate so as to reinforce and / or support the polarizing plate. When the polarizing plate contains a pressure-sensitive adhesive layer, a separator is temporarily attached to the surface of the pressure-sensitive adhesive layer so that the pressure-sensitive adhesive layer is protected until actual use, and the polarizing plate can be rolled.

In the embodiment of the present invention, the first protective layer 20 is composed of a solidified coating film of an organic solvent solution of a thermoplastic acrylic resin. With such a configuration, the protective layer can be made very thin (for example, 10 μm or less). In addition, the protective layer can be formed directly on the polarizer (ie, without the intervention of an adhesive layer or an adhesive layer). According to the embodiment of the present invention, as described above, the polarizer and the first protective layer are very thin, and the adhesive layer or the adhesive layer can be omitted, so that the total thickness of the polarizing plate is very large. Can be thinned. The second protective layer is made of a resin film. By forming the second protective layer with a resin film, the handleability of the polarizing plate (for example, roll transportability) can be ensured.

The total thickness of the polarizing plate is, for example, 50 μm or less, preferably 45 μm or less, more preferably 40 μm or less, and further preferably 35 μm or less. The lower limit of the total thickness of the polarizing plate can be, for example, 25 μm.

Further, in the embodiment of the present invention, the glass transition temperature (Tg) of the first protective layer 20 is 95 ° C. or higher, preferably 100 ° C. or higher, more preferably 105 ° C. or higher, still more preferably. It is 110 ° C. or higher, and particularly preferably 115 ° C. or higher. When the Tg of the first protective layer is within such a range, protective layers are arranged on both sides of the polarizing element, and the first protective layer is a solidified coating film of an organic solvent solution of a thermoplastic acrylic resin. Due to the synergistic effect with the effect of the above, it is possible to realize a polarizing plate having excellent durability even though it is very thin. Specifically, it is possible to realize a polarizing plate in which deterioration of optical characteristics is suppressed even in a heating and humidifying environment. On the other hand, the Tg of the first protective layer is preferably 300 ° C. or lower, more preferably 250 ° C. or lower, still more preferably 200 ° C. or lower, and particularly preferably 160 ° C. or lower. When the Tg of the first protective layer is in such a range, the moldability can be excellent.

As described above, according to the embodiment of the present invention, it is possible to realize a polarizing plate in which deterioration of optical characteristics is suppressed even in a heating and humidifying environment. In such a polarizing plate, the amount of change ΔTs of the simple substance transmittance Ts and the amount of change ΔP of the degree of polarization P after being left in an environment of 85 ° C. and 85% RH for 48 hours are very small, respectively. The simple substance transmittance Ts can be measured using, for example, an ultraviolet-visible spectrophotometer (manufactured by JASCO Corporation, product name "V7100"). The degree of polarization P is calculated by the following equation from the single transmittance (Ts), the parallel transmittance (Tp) and the orthogonal transmittance (Tc) measured using an ultraviolet-visible spectrophotometer.
Polarization degree (P) (%) = {(Tp-Tc) / (Tp + Tc)} ^1/2 × 100
The Ts, Tp, and Tc are Y values measured by the JIS Z 8701 2 degree field of view (C light source) and corrected for luminosity factor. Also, Ts and P are substantially properties of the polarizer. ΔTs and ΔP are calculated by the following formulas, respectively.
ΔTs (%) = Ts ₄₈ −Ts ₀
ΔP (%) = P ₄₈ −P ₀
Here, Ts ₀ is the single transmittance before leaving (initial), Ts ₄₈ is the single transmittance after leaving, P ₀ is the degree of polarization before leaving (initial), and P ₄₈ is after leaving. The degree of polarization. ΔTs is preferably 3.0% or less, more preferably 2.7% or less, still more preferably 2.4% or less. ΔP is preferably −0.05% to 0%, more preferably −0.03% to 0%, and even more preferably −0.01% to 0%.

Since the polarizing plate of the present invention is very thin as described above, it can be suitably applied to a flexible image display device. More preferably, the image display device has a curved shape (substantially a curved display screen) and / or is bendable or bendable. Specific examples of the image display device include a liquid crystal display device and an electroluminescence (EL) display device (for example, an organic EL display device and an inorganic EL display device). Needless to say, the above description does not prevent the polarizing plate of the present invention from being applied to a normal image display device.

Hereinafter, the polarizer and the protective layer will be described in detail.

B. Polarizer As the polarizer, any suitable polarizer can be adopted. The polarizer can typically be made using a laminate of two or more layers. The method for manufacturing the polarizer will be described later in Section D as a method for manufacturing the polarizing plate.

The thickness of the polarizer is preferably 1 μm to 8 μm, more preferably 1 μm to 7 μm, and even more preferably 2 μm to 5 μm.

The boric acid content of the polarizer is preferably 10% by weight or more, more preferably 13% by weight to 25% by weight. When the boric acid content of the polarizer is in such a range, the ease of curl adjustment at the time of bonding is well maintained due to the synergistic effect with the iodine content described later, and the curl at the time of heating is maintained. It is possible to improve the appearance durability at the time of heating while satisfactorily suppressing the above. The boric acid content can be calculated as, for example, the amount of boric acid contained in the polarizer per unit weight by using the following formula from the neutralization method.

The iodine content of the polarizer is preferably 2% by weight or more, more preferably 2% by weight to 10% by weight. When the iodine content of the polarizer is in such a range, the ease of curl adjustment at the time of bonding is well maintained due to the synergistic effect with the above boric acid content, and the curl at the time of heating is maintained. It is possible to improve the appearance durability at the time of heating while satisfactorily suppressing the above. As used herein, the term "iodine content" means the amount of all iodine contained in the polarizer (PVA-based resin film). More specifically, in the polarizer, iodine exists in the form of ^{iodine ion (I −} ), iodine molecule (I ₂ ), polyiodine ion (I ₃ ⁻ , I ₅ ^{−) and the like.} Iodine content means the amount of iodine that includes all of these forms. The iodine content can be calculated, for example, by the calibration curve method of fluorescent X-ray analysis. The polyiodine ion exists in a state in which a PVA-iodine complex is formed in the polarizer. By forming such a complex, absorption dichroism can be exhibited in the wavelength range of visible light. Specifically, a complex of PVA and tri-iodide ion (PVA · _{I 3} ^-) has a light absorption peak around 470 nm, a complex of PVA and five iodide ion (PVA · _{I 5} ^-) is 600nm near Has an absorptive peak. As a result, polyiodine ions can absorb light over a wide range of visible light, depending on their morphology. On the other hand, iodine ion (I ⁻ ) has an absorption peak near 230 nm and is not substantially involved in the absorption of visible light. Therefore, polyiodine ions present in the form of a complex with PVA may be mainly involved in the absorption performance of the polarizer.

The polarizer preferably exhibits absorption dichroism at any wavelength of 380 nm to 780 nm. The simple substance transmittance Ts of the polarizer is preferably 40% to 48%, more preferably 41% to 46%. The degree of polarization P of the polarizer is preferably 97.0% or more, more preferably 99.0% or more, and further preferably 99.9% or more.

C. Protective layer C-1. First Protective Layer As described above, the first protective layer is composed of a solidified coating film of an organic solvent solution of a thermoplastic acrylic resin (hereinafter, simply referred to as an acrylic resin). Hereinafter, the constituent components of the first protective layer will be specifically described, and then the characteristics of the first protective layer will be described.

C-1-1. Acrylic resin The Tg of an acrylic resin (including a blend of two or more kinds of acrylic resins and a blend of an acrylic resin and another resin as described later) is described in the above section A with respect to the first protective layer. As you did.

As the acrylic resin, any suitable acrylic resin can be adopted as long as it has Tg as described above. Acrylic resins typically contain an alkyl (meth) acrylate as a main component as a monomer unit (repeating unit). As used herein, the term "(meth) acrylic" means acrylic and / or methacryl. Examples of the alkyl (meth) acrylate constituting the main skeleton of the acrylic resin include those having a linear or branched alkyl group having 1 to 18 carbon atoms. These can be used alone or in combination. Further, any suitable copolymerization monomer may be introduced into the acrylic resin by copolymerization. The repeating unit derived from alkyl (meth) acrylate is typically represented by the following general formula (1):

In the general formula (1), R ⁴ represents a hydrogen atom or a methyl group, and R ⁵ represents a hydrogen atom or an aliphatic or alicyclic hydrocarbon group having 1 to 6 carbon atoms which may be substituted. show. Examples of the substituent include halogens and hydroxyl groups. Specific examples of alkyl (meth) acrylate include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, n-butyl (meth) acrylate, and t-butyl (meth) acrylate. Butyl, n-hexyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, benzyl (meth) acrylate, dicyclopentanyloxyethyl (meth) acrylate, (meth) acrylic Dicyclopentanyl acid, chloromethyl (meth) acrylate, 2-chloroethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2, (meth) acrylate 2, 3,4,5,6-pentahydroxyhexyl, (meth) acrylate 2,3,4,5-tetrahydroxypentyl, methyl 2- (hydroxymethyl) acrylate, ethyl 2- (hydroxymethyl) acrylate, 2 -(Hydroxyethyl) methyl acrylate can be mentioned. In the general formula (1), R ⁵ is preferably a hydrogen atom or a methyl group. Therefore, a particularly preferred alkyl (meth) acrylate is methyl acrylate or methyl methacrylate.

Acrylic resins may also include only a single alkyl (meth) acrylate units, even if R ⁴ and R ⁵ include a plurality of different alkyl (meth) acrylate unit in the above general formula (1) good.

The content ratio of the alkyl (meth) acrylate unit in the acrylic resin is preferably 50 mol% to 98 mol%, more preferably 55 mol% to 98 mol%, still more preferably 60 mol% to 98 mol%, and particularly preferably. It is 65 mol% to 98 mol%, most preferably 70 mol% to 97 mol%. If the content ratio is less than 50 mol%, the effects expressed from the alkyl (meth) acrylate unit (for example, high heat resistance and high transparency) may not be sufficiently exhibited. If the content ratio is more than 98 mol%, the resin is brittle and easily cracked, high mechanical strength cannot be sufficiently exhibited, and productivity may be inferior.

The acrylic resin preferably has a repeating unit containing a ring structure. Examples of the repeating unit including a ring structure include a lactone ring unit, a glutaric anhydride unit, a glutarimide unit, a maleic anhydride unit, and a maleimide (N-substituted maleimide) unit. Only one type of the repeating unit including the ring structure may be contained in the repeating unit of the acrylic resin, or two or more types may be contained.

The lactone ring unit is preferably represented by the following general formula (2):

一般式（２）において、Ｒ^１、Ｒ^２およびＲ^３は、それぞれ独立して、水素原子または炭素数１〜２０の有機残基を表す。なお、有機残基は酸素原子を含んでいてもよい。アクリル系樹脂には、単一のラクトン環単位のみが含まれていてもよく、上記一般式（２）におけるＲ^１、Ｒ^２およびＲ^３が異なる複数のラクトン環単位が含まれていてもよい。ラクトン環単位を有するアクリル系樹脂は、例えば特開２００８−１８１０７８号公報に記載されており、当該公報の記載は本明細書に参考として援用される。

In the general formula (2), R ¹ , R ² and R ³ independently represent a hydrogen atom or an organic residue having 1 to 20 carbon atoms. The organic residue may contain an oxygen atom. The acrylic resin may be contained only a single lactone ring units may be R ^1, R ² and R ³ in the general formula (2) is contains different lactone ring unit .. An acrylic resin having a lactone ring unit is described in, for example, Japanese Patent Application Laid-Open No. 2008-181078, and the description in this publication is incorporated herein by reference.

The glutarimide unit is preferably represented by the following general formula (3):

In the general formula (3), R ¹¹ and R ¹² independently represent hydrogen or an alkyl group having 1 to 8 carbon atoms, and R ¹³ is an alkyl group having 1 to 18 carbon atoms and 3 to 12 carbon atoms. The cycloalkyl group of the above, or an aryl group having 6 to 10 carbon atoms is shown. In the general formula (3), preferably R ¹¹ and R ¹² are independently hydrogen or methyl groups, and R ¹³ is a hydrogen, methyl group, butyl group or cyclohexyl group, respectively. More preferably, R ¹¹ is a methyl group, R ¹² is hydrogen, and R ¹³ is a methyl group. The acrylic resin may contain only a single glutarimide unit, or may contain a plurality of glutarimide units having different ^{R 11} , R ¹² and R ^{13 in the above general formula (3).} .. Examples of the acrylic resin having a glutarimide unit include JP-A-2006-309033, JP-A-2006-317560, JP-A-2006-328334, JP-A-2006-337491, and JP-A-2006-337492. It is described in Japanese Patent Application Laid-Open No. 2006-337493 and Japanese Patent Application Laid-Open No. 2006-337569, and the description of the relevant publication is incorporated herein by reference. Note that the glutaric anhydride units, nitrogen atom substituted by R ¹³ in the general formula (3), except that the oxygen atom, the above description is applied about the glutarimide units.

Since the structure of the maleic anhydride unit and the maleimide (N-substituted maleimide) unit is specified from the name, specific description thereof will be omitted.

The content ratio of the repeating unit including the ring structure in the acrylic resin is preferably 1 mol% to 50 mol%, more preferably 10 mol% to 40 mol%, and further preferably 20 mol% to 30 mol%. If the content ratio is too small, the Tg may be less than 110 ° C., and the heat resistance, solvent resistance and surface hardness of the obtained first protective layer may be insufficient. If the content is too high, moldability and transparency may be insufficient.

The acrylic resin may contain a repeating unit other than the alkyl (meth) acrylate unit and the repeating unit including the ring structure. Examples of such a repeating unit include a repeating unit derived from a vinyl-based monomer copolymerizable with the monomer constituting the above unit (another vinyl-based monomer unit). Examples of other vinyl-based monomers include acrylic acid, methacrylic acid, crotonic acid, 2- (hydroxymethyl) acrylic acid, 2- (hydroxyethyl) acrylic acid, acrylonitrile, methacrylonitrile, etacrylonitrile, and allyl. Glycidyl ether, maleic anhydride, itaconic anhydride, N-methylmaleimide, N-ethylmaleimide, N-cyclohexylmaleimide, aminoethyl acrylate, propylaminoethyl acrylate, dimethylaminoethyl methacrylate, ethylaminopropyl methacrylate, methacryl Cyclohexylaminoethyl acid, N-vinyldiethylamine, N-acetylvinylamine, allylamine, metaallylamine, N-methylallylamine, 2-isopropenyl-oxazoline, 2-vinyl-oxazoline, 2-acroyl-oxazoline, N-phenylmaleimide, Examples thereof include phenylaminoethyl methacrylate, styrene, α-methylstyrene, p-glycidylstyrene, p-aminostyrene, and 2-styryl-oxazoline. These may be used alone or in combination. The type, number, combination, content ratio, etc. of other vinyl-based monomer units can be appropriately set according to the purpose.

The weight average molecular weight of the acrylic resin is preferably 1,000,000 to 2000000, more preferably 5000 to 1000000, still more preferably 1000 to 500000, particularly preferably 50,000 to 500000, and most preferably 60000 to 150,000. The weight average molecular weight can be determined by polystyrene conversion using, for example, a gel permeation chromatograph (GPC system, manufactured by Tosoh). Tetrahydrofuran can be used as the solvent.

The acrylic resin can be polymerized by any suitable polymerization method using the above-mentioned monomer units in an appropriate combination. Two or more acrylic resins having different monomer units may be blended.

In the embodiment of the present invention, the acrylic resin and another resin may be used in combination. That is, the monomer component constituting the acrylic resin and the monomer component constituting the other resin may be copolymerized, and the copolymer may be used for molding the first protective layer described later; the acrylic resin and others. The blend with the resin of the above may be used for forming the first protective layer. Examples of other resins include thermoplastic resins such as styrene resin, polyethylene, polypropylene, polyamide, polyphenylene sulfide, polyether ether ketone, polyester, polysulfone, polyphenylene oxide, polyacetal, polyimide, and polyetherimide. The type and blending amount of the resin to be used in combination can be appropriately set according to the purpose and the desired properties of the obtained film. For example, a styrene resin (preferably an acrylonitrile-styrene copolymer) can be used in combination as a retardation control agent.

When the acrylic resin is used in combination with another resin, the content of the acrylic resin in the blend of the acrylic resin and the other resin is preferably 50% by weight to 100% by weight, more preferably 60% by weight to 100% by weight. By weight%, more preferably 70% by weight to 100% by weight, particularly preferably 80% by weight to 100% by weight. If the content is less than 50% by weight, the high heat resistance and high transparency inherent in the acrylic resin may not be sufficiently reflected.

C-1-2. Structure and Characteristics of First Protective Layer As described above, the first protective layer is composed of a solidified coating film of an organic solvent solution of an acrylic resin. With such a solidified coating film, the thickness can be significantly reduced as compared with the extrusion-molded film. The thickness of the first protective layer is 10 μm or less, preferably 7 μm or less, more preferably 5 μm or less, and further preferably 3 μm or less as described above. The lower limit of the thickness of the first protective layer can be, for example, 1 μm. Further, although it is not theoretically clear, such a solidified coating film is compared with a cured product of a thermosetting resin or an active energy ray-curable resin (for example, an ultraviolet curable resin) at the time of film molding. Since the shrinkage is small and the residual monomer or the like is not contained, deterioration of the film itself can be suppressed, and the adverse effect on the polarizing plate (polarizer) caused by the residual monomer or the like can be suppressed. Further, it has an advantage that it is excellent in humidification durability because it has low hygroscopicity and moisture permeability as compared with a solidified water-based coating film such as an aqueous solution or an aqueous dispersion. As a result, it is possible to realize a polarizing plate having excellent durability that can maintain the optical characteristics even in a heating and humidifying environment.

The Tg of the first protective layer is as described in Section A above.

The amount of iodine adsorbed by the first protective layer is preferably 4.0% by weight or less, more preferably 3.0% by weight or less, still more preferably 2.0% by weight or less, and particularly preferably 1. It is 0.0% by weight or less, and particularly preferably 0.5% by weight or less. The smaller the amount of iodine adsorbed, the more preferable, and the lower limit thereof can be, for example, 0.1% by weight. If the amount of iodine adsorbed is in such a range, a polarizing plate having even better durability can be obtained. The iodine adsorption amount can be measured by the method described in Examples described later.

The first protective layer is preferably substantially optically isotropic. In the present specification, "substantially optically isotropic" means that the in-plane retardation Re (550) is 0 nm to 10 nm and the thickness direction retardation Rth (550) is −20 nm to +10 nm. Say something. The in-plane retardation Re (550) is more preferably 0 nm to 5 nm, further preferably 0 nm to 3 nm, and particularly preferably 0 nm to 2 nm. The phase difference Rth (550) in the thickness direction is more preferably −5 nm to + 5 nm, further preferably -3 nm to + 3 nm, and particularly preferably -2 nm to + 2 nm. When Re (550) and Rth (550) of the first protective layer are in such a range, adverse effects on the display characteristics are prevented when the polarizing plate including the first protective layer is applied to the image display device. be able to. Re (550) is an in-plane phase difference of the film measured with light having a wavelength of 550 nm at 23 ° C. Re (550) is calculated by the formula: Re (550) = (nx-ny) × d. Rth (550) is a phase difference in the thickness direction of the film measured with light having a wavelength of 550 nm at 23 ° C. Rth (550) is calculated by the formula: Rth (550) = (nx-nz) × d. Here, nx is the refractive index in the direction in which the in-plane refractive index is maximized (that is, the slow-phase axis direction), and ny is the in-plane direction orthogonal to the slow-phase axis (that is, the phase-advancing axis direction). It is the refractive index, nz is the refractive index in the thickness direction, and d is the thickness (nm) of the film.

The higher the light transmittance at 380 nm at a thickness of 3 μm of the first protective layer, the more preferable. Specifically, the light transmittance is preferably 85% or more, more preferably 88% or more, still more preferably 90% or more. When the light transmittance is in such a range, the desired transparency can be ensured. The light transmittance can be measured, for example, by a method according to ASTM-D-1003.

The lower the haze of the first protective layer, the more preferable. Specifically, the haze is preferably 5% or less, more preferably 3% or less, still more preferably 1.5% or less, and particularly preferably 1% or less. When the haze is 5% or less, a good clear feeling can be given to the film. Further, even when the polarizing plate on the visual side of the image display device is used, the displayed contents can be visually recognized satisfactorily.

The YI of the first protective layer at a thickness of 3 μm is preferably 1.27 or less, more preferably 1.25 or less, still more preferably 1.23 or less, and particularly preferably 1.20 or less. If the YI exceeds 1.3, the optical transparency may be insufficient. The YI is obtained from, for example, the tristimulus values (X, Y, Z) of the color obtained by measurement using a high-speed integrating sphere type spectral transmittance measuring machine (trade name: DOT-3C: manufactured by Murakami Color Technology Laboratory). , Can be calculated by the following equation.
YI = [(1.28X-1.06Z) / Y] x 100

The b value (a measure of hue according to the hunter's color system) at a thickness of 3 μm of the first protective layer is preferably less than 1.5, more preferably 1.0 or less. When the b value is 1.5 or more, an undesired color may appear. For the b value, for example, a sample of the film constituting the first protective layer is cut into 3 cm squares, and a high-speed integrating sphere type spectral transmittance measuring machine (trade name: DOT-3C: manufactured by Murakami Color Technology Laboratory) is used. It can be obtained by measuring the hue using the product and evaluating the hue according to the hunter's color system.

The first protective layer (solidified coating film) may contain any suitable additive depending on the purpose. Specific examples of additives include ultraviolet absorbers; leveling agents; antioxidants such as hindered phenol-based, phosphorus-based, and sulfur-based; stabilizers such as light-resistant stabilizers, weather-resistant stabilizers, and heat-stabilizing agents; glass fibers, Reinforcing materials such as carbon fibers; Near infrared absorbers; Flame retardants such as tris (dibromopropyl) phosphate, triallyl phosphate, antimony oxide; Antistatic agents such as anionic, cationic and nonionic surfactants; Inorganic pigments , Organic pigments, colorants such as dyes; organic fillers or inorganic fillers; resin modifiers; organic fillers and inorganic fillers; plasticizers; lubricants; antistatic agents; flame retardants; and the like. The additive may be added at the time of polymerization of the acrylic resin, or may be added to the solution at the time of film formation. The type, number, combination, amount of additive, etc. of the additive can be appropriately set according to the purpose.

An easy-adhesion layer may be formed on the polarizer side of the first protective layer. The easy-adhesion layer contains, for example, an aqueous polyurethane and an oxazoline-based cross-linking agent. By forming such an easy-adhesion layer, the adhesion between the first protective layer and the polarizer can be enhanced.

C-2. Second Protective Layer The second protective layer is made of a resin film as described above. Specific examples of the material that is the main component of the film include cellulose resins such as triacetyl cellulose (TAC), polyester resins such as polyethylene terephthalate (PET), polyvinyl alcohol resins, polycarbonate resins, and polyamide resins. Examples thereof include a polyimide resin, a polyether sulfone resin, a polysulfone resin, a polystyrene resin, a cycloolefin resin such as polynorbornene, a polyolefin resin, a (meth) acrylic resin, and a transparent resin such as an acetate resin. Further, thermosetting resins such as (meth) acrylic, urethane, (meth) acrylic urethane, epoxy, and silicone, or ultraviolet curable resins can also be mentioned. In addition to this, for example, glassy polymers such as siloxane-based polymers can also be mentioned. Further, the polymer film described in Japanese Patent Application Laid-Open No. 2001-343529 (WO01 / 37007) can also be used. As the material of this film, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted imide group in the side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group in the side chain. Can be used, and examples thereof include a resin composition having an alternating copolymer composed of isobutene and N-methylmaleimide and an acrylonitrile / styrene copolymer. The polymer film can be, for example, an extruded product of the above resin composition.

When the polarizing plate of the present invention is arranged on the visual side of the image display device and the second protective layer 30 is arranged on the opposite side (visual side) of the display cell of the image display device, the second protective layer 30 May be subjected to surface treatment such as hard coating treatment, antireflection treatment, anti-sticking treatment, anti-glare treatment and the like, if necessary. Further / or, if necessary, the second protective layer 30 is provided with a process for improving visibility when visually recognizing through polarized sunglasses (typically, a (elliptical) circularly polarized light function is imparted. (Giving an ultra-high phase difference) may be applied. By performing such processing, excellent visibility can be realized even when the display screen is visually recognized through a polarized lens such as polarized sunglasses. Therefore, the polarizing plate can also be suitably applied to an image display device that can be used outdoors.

The thickness of the second protective layer is preferably 10 μm to 50 μm, more preferably 10 μm to 30 μm. When the surface treatment is applied, the thickness of the outer protective layer is the thickness including the thickness of the surface treatment layer.

D. Method for manufacturing polarizing plate D-1. Method for producing a polarizer The method for producing a polarizer according to the above item B is a polyvinyl alcohol-based resin containing a halide and a polyvinyl alcohol-based resin (PVA-based resin) on one side of a long thermoplastic resin base material. A layer (PVA-based resin layer) is formed to form a laminated body, and the laminated body is heated in the width direction while being conveyed in the longitudinal direction by aerial auxiliary stretching treatment, dyeing treatment, and underwater stretching treatment. A drying shrinkage treatment for shrinking by 2% or more, and a drying shrinkage treatment, which are performed in this order, are included. The content of the halide in the PVA-based resin layer is preferably 5 parts by weight to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin. The drying shrinkage treatment is preferably carried out using a heating roll, and the temperature of the heating roll is preferably 60 ° C. to 120 ° C. According to such a manufacturing method, the above-mentioned polarizer can be obtained. In particular, by preparing a laminate containing a PVA-based resin layer containing a halide, stretching the laminate to multi-step stretching including aerial auxiliary stretching and underwater stretching, and heating the stretched laminate with a heating roll. It is possible to obtain a polarizer having excellent optical characteristics (typically, single transmittance and degree of polarization) and suppressing variation in optical characteristics. Specifically, by using a heating roll in the drying shrinkage treatment step, the laminated body can be uniformly shrunk over the entire laminated body while being conveyed. As a result, not only the optical characteristics of the obtained polarizer can be improved, but also a polarizer having excellent optical characteristics can be stably produced, and the variation in the optical characteristics of the polarizer (particularly, the single transmittance) can be suppressed. can do. Hereinafter, the halide and the drying shrinkage treatment will be described. Details of manufacturing methods other than these are described in, for example, Japanese Patent Application Laid-Open No. 2012-73580. The entire description of the publication is incorporated herein by reference.

D-1-1. Halide A PVA-based resin layer containing a halide and a PVA-based resin can be formed by applying a coating liquid containing a halide and a PVA-based resin onto a thermoplastic resin base material and drying the coating film. The coating liquid is typically a solution in which the above-mentioned halide and the above-mentioned PVA-based resin are dissolved in a solvent. Examples of the solvent include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylpropane, and amines such as ethylenediamine and diethylenetriamine. These can be used alone or in combination of two or more. Of these, water is preferred. The PVA-based resin concentration of the solution is preferably 3 parts by weight to 20 parts by weight with respect to 100 parts by weight of the solvent. With such a resin concentration, a uniform coating film can be formed in close contact with the thermoplastic resin base material.

As the halide, any suitable halide can be adopted. For example, iodide and sodium chloride can be mentioned. Iodides include, for example, potassium iodide, sodium iodide, and lithium iodide. Of these, potassium iodide is preferred.

The amount of the halide in the coating liquid is preferably 5 parts by weight to 20 parts by weight, and more preferably 10 parts by weight to 15 parts by weight with respect to 100 parts by weight of the PVA-based resin. If the amount of the halide is too large, the halide may bleed out and the finally obtained polarizer may become cloudy.

Generally, the stretching of the PVA-based resin layer increases the orientation of the polyvinyl alcohol molecules in the PVA-based resin. However, when the stretched PVA-based resin layer is immersed in a liquid containing water, the polyvinyl alcohol molecules become more oriented. The orientation may be disturbed and the orientation may decrease. In particular, when the laminate of the thermoplastic resin base material and the PVA-based resin layer is stretched in boric acid water, the laminate is stretched in boric acid water at a relatively high temperature in order to stabilize the stretching of the thermoplastic resin base material. When stretched, the tendency of the degree of orientation to decrease is remarkable. For example, while stretching a PVA film alone in boric acid water is generally performed at 60 ° C., stretching of a laminate of A-PET (thermoplastic resin base material) and a PVA-based resin layer is performed. It is carried out at a high temperature of about 70 ° C., and in this case, the orientation of PVA at the initial stage of stretching may decrease before it is increased by stretching in water. On the other hand, a laminate of a PVA-based resin layer containing a halide and a thermoplastic resin base material is prepared, and the laminate is stretched at a high temperature (auxiliary stretching) in the air before being stretched in boric acid water. , Crystallization of the PVA-based resin in the PVA-based resin layer of the laminated body after the auxiliary stretching can be promoted. As a result, when the PVA-based resin layer is immersed in a liquid, the disorder of the orientation of the polyvinyl alcohol molecules and the decrease in the orientation can be suppressed as compared with the case where the PVA-based resin layer does not contain a halide. As a result, the optical characteristics of the polarizer obtained through a treatment step of immersing the laminate in a liquid, such as a dyeing treatment and a stretching treatment in water, can be improved.

D-1-2. Dry shrinkage treatment The dry shrinkage treatment may be carried out by heating the entire zone by zone heating, or by heating the transport roll (using a so-called heating roll) (heating roll drying method). Preferably, both are used. By drying using a heating roll, it is possible to efficiently suppress the heating curl of the laminate and produce a polarizer having an excellent appearance. Specifically, by drying the laminate along the heating roll, the crystallization of the thermoplastic resin base material can be efficiently promoted and the crystallinity can be increased, which is relatively low. Even at the drying temperature, the crystallinity of the thermoplastic resin base material can be satisfactorily increased. As a result, the rigidity of the thermoplastic resin base material is increased, and the thermoplastic resin base material is in a state of being able to withstand the shrinkage of the PVA-based resin layer due to drying, and curling is suppressed. Further, by using the heating roll, the laminated body can be dried while being maintained in a flat state, so that not only curl but also wrinkles can be suppressed. At this time, the laminated body can be improved in optical characteristics by shrinking in the width direction by a drying shrinkage treatment. This is because the orientation of PVA and the PVA / iodine complex can be effectively enhanced. The shrinkage ratio in the width direction of the laminate by the drying shrinkage treatment is preferably 2% to 10%, more preferably 2% to 8%, and particularly preferably 4% to 6%. By using the heating roll, the laminated body can be continuously contracted in the width direction while being conveyed, and high productivity can be realized.

FIG. 2 is a schematic view showing an example of the drying shrinkage treatment. In the drying shrinkage treatment, the laminate 200 is dried while being transported by the transport rolls R1 to R6 heated to a predetermined temperature and the guide rolls G1 to G4. In the illustrated example, the transport rolls R1 to R6 are arranged so as to alternately and continuously heat the surface of the PVA resin layer and the surface of the thermoplastic resin base material. The transport rolls R1 to R6 may be arranged so as to continuously heat only the resin base material surface).

The drying conditions can be controlled by adjusting the heating temperature of the transport roll (temperature of the heating roll), the number of heating rolls, the contact time with the heating roll, and the like. The temperature of the heating roll is preferably 60 ° C. to 120 ° C., more preferably 65 ° C. to 100 ° C., and particularly preferably 70 ° C. to 80 ° C. The crystallinity of the thermoplastic resin can be satisfactorily increased, curling can be satisfactorily suppressed, and an optical laminate having extremely excellent durability can be produced. The temperature of the heating roll can be measured with a contact thermometer. In the illustrated example, six transport rolls are provided, but there is no particular limitation as long as there are a plurality of transport rolls. The number of transport rolls is usually 2 to 40, preferably 4 to 30. The contact time (total contact time) between the laminate and the heating roll is preferably 1 second to 300 seconds, more preferably 1 to 20 seconds, and further preferably 1 to 10 seconds.

The heating roll may be provided in a heating furnace (for example, an oven) or in a normal production line (in a room temperature environment). Preferably, it is provided in a heating furnace provided with a blowing means. By using both drying with a heating roll and hot air drying together, a steep temperature change between the heating rolls can be suppressed, and shrinkage in the width direction can be easily controlled. The temperature of hot air drying is preferably 30 ° C to 100 ° C. The hot air drying time is preferably 1 second to 300 seconds. The wind speed of hot air is preferably about 10 m / s to 30 m / s. The wind speed is the wind speed in the heating furnace and can be measured by a mini-vane type digital anemometer.

Preferably, a washing treatment is performed after the underwater stretching treatment and before the drying shrinkage treatment. The cleaning treatment is typically performed by immersing a PVA-based resin layer in an aqueous potassium iodide solution.

In this way, a laminate of a thermoplastic resin base material / polarizer can be obtained.

D-2. Method for manufacturing a polarizing plate A resin film constituting a second protective layer is attached to the surface of the polarizer of the laminate obtained in the above item D-1. Next, the thermoplastic resin base material is peeled off, an organic solvent solution of an acrylic resin is applied to the peeled surface to form a coating film, and the coating film is solidified to form a first protective layer. In this way, a polarizing plate having a structure of a first protective layer (solidified coating film) / polarizer / second protective layer (resin film) can be obtained.

The acrylic resin is as described in Section C-1-1 above.

As the organic solvent, any suitable organic solvent capable of dissolving or uniformly dispersing the acrylic resin can be used. Specific examples of the organic solvent include ethyl acetate, toluene, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), cyclopentanone, and cyclohexanone.

The concentration of the acrylic resin in the solution is preferably 3 parts by weight to 20 parts by weight with respect to 100 parts by weight of the solvent. With such a resin concentration, a uniform coating film in close contact with the polarizer can be formed.

The solution may be applied to any suitable substrate or to a polarizer. When the solution is applied to the base material, the solidified material of the coating film formed on the base material is transferred to the polarizer. When the solution is applied to the polarizer, the coating film is dried (solidified) so that the first protective layer is directly formed on the polarizer. Preferably, the solution is applied to the polarizer and a first protective layer is formed directly on the polarizer. With such a configuration, the adhesive layer or the pressure-sensitive adhesive layer required for transfer can be omitted, so that the polarizing plate can be further thinned. Any suitable method can be adopted as the method for applying the solution. Specific examples include a roll coating method, a spin coating method, a wire bar coating method, a dip coating method, a die coating method, a curtain coating method, a spray coating method, and a knife coating method (comma coating method, etc.).

A first protective layer can be formed by drying (solidifying) the coating film of the solution. The drying temperature is preferably 100 ° C. or lower, more preferably 50 ° C. to 70 ° C. When the drying temperature is in such a range, it is possible to prevent an adverse effect on the polarizer. The drying time can vary depending on the drying temperature. The drying time can be, for example, 1 minute to 10 minutes.

As described above, a polarizing plate having a structure of a first protective layer (solidified coating film) / polarizer / second protective layer (resin film) can be obtained. Alternatively, the thermoplastic resin base material may be used as it is as the second protective layer. In this case, a coating film is formed by applying an organic solvent solution of an acrylic resin to the polarizer surface of the laminate of the thermoplastic resin base material / polarizer, and the coating film is solidified to provide the first protection. A layer is formed, and as a result, a polarizing plate having a structure of a first protective layer (solidified coating film) / polarizer / second protective layer (thermoplastic resin base material) can be obtained.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples. The measurement method of each characteristic is as follows. Unless otherwise specified, "parts" and "%" in the examples are based on weight.

(1) Glass transition temperature Tg
A solution prepared by dissolving the material constituting the first protective layer used in Examples and Comparative Examples in a predetermined solvent was applied to a base material (PET film) by an applicator, dried at 60 ° C., and coated (thickness 40 μm). ) Was formed. The obtained coating film was peeled off from the base material and cut into strips to prepare a measurement sample. The measurement sample was subjected to DMA measurement, and Tg was measured. The measuring device and measuring conditions were as follows.
(measuring device)
"DMS6100" manufactured by SII Nanotechnology Inc.
(Measurement condition)
-Measurement temperature range: -80 ° C to 150 ° C
・ Elevating temperature: 2 ℃ / min ・ Measurement sample width: 10mm
・ Distance between chucks: 20 mm
・ Measurement frequency: 1Hz
・ Strain amplitude: 10 μm
・ Measurement atmosphere: N ₂ (250 mL / min)
(2) Amount of Iodine Adsorption A solution prepared by dissolving the material constituting the first protective layer used in Examples and Comparative Examples in a predetermined solvent was applied to a base material (PET film) by an applicator and dried at 60 ° C. A coating film (thickness 40 μm) was formed. The obtained coating film was peeled off from the base material ^{and cut into 1 cm × 1 cm (1 cm 2} ) to prepare a measurement sample. The measurement sample was subjected to a combustion IC method, and the amount of iodine in the sample was quantitatively analyzed. Specifically, it is as follows. The measurement sample was collected and weighed in a headspace vial (20 mL volume). Next, a vial (2 mL volume) containing 1 mL of an iodine solution (iodine concentration 1% by weight, potassium iodide concentration 7% by weight) was placed in this headspace vial and sealed. After that, this headspace vial is heated in a dryer at 65 ° C. for 6 hours, the heated sample is collected in a ceramic port and burned using an automatic combustion device, and the generated gas is collected in an absorbing liquid and then quantified. The analysis was performed to determine the weight% of the adsorbed iodine. The equipment used was as follows.
-Automatic sample combustion device: "AQF-2100H" manufactured by Mitsubishi Chemical Analytical Co., Ltd.
-IC (anion): "ICS-3000" manufactured by Thermo Fisher Scientific.
(3) Color loss From the polarizing plates obtained in Examples and Comparative Examples, a test piece (50 mm × 50 mm) having two sides opposite to each other in the direction orthogonal to the absorption axis direction of the polarizer and the absorption axis direction was cut out. .. The test piece was attached to a non-alkali glass plate with an adhesive so that the first protective layer was on the inside to form a test sample, and the test sample was left in an oven at 85 ° C. and 85% RH for 48 hours for heating and humidification. Then, the color loss state of the polarizing plate after humidification when placed in the state of the standard polarizing plate and the cross Nicol was visually examined and evaluated according to the following criteria.
No problem: No color loss was observed Partial loss: Color loss was observed at the edges Total loss: Color loss was remarkable throughout the polarizing plate (4) Single transmittance and degree of polarization Example and comparison From the polarizing plate obtained in the example, a test piece (50 mm × 50 mm) having two sides facing each other in the direction orthogonal to the absorption axis direction of the polarizer and the absorption axis direction was cut out. The test piece was attached to a non-alkali glass plate with an adhesive so that the protective layer was on the outside to form a test sample, and an ultraviolet-visible spectrophotometer (manufactured by JASCO Corporation, product name "V7100") was used for the test sample. Then, the single transmittance (Ts), the parallel transmittance (Tp) and the orthogonal transmittance (Tc) were measured, and the degree of polarization (P) was calculated by the following equation. At this time, the measurement light was incident from the protective layer side.
Polarization degree (P) (%) = {(Tp-Tc) / (Tp + Tc)} ^1/2 × 100
The Ts, Tp, and Tc are Y values measured by the JIS Z 8701 2 degree field of view (C light source) and corrected for luminosity factor. Also, Ts and P are substantially properties of the polarizer.
Next, the polarizing plate was left in an oven at 85 ° C. and 85% RH for 48 hours to heat and humidify (heating test), _{and from the single transmittance Ts 0} before the heating test and the single transmittance Ts ₄₈ after the heating test, The amount of change in single transmittance ΔTs was determined using the following formula.
ΔTs (%) = Ts ₄₈ −Ts ₀
Similarly, from the degree of polarization P ₀ before the heating test and the degree of polarization P ₄₈ after the heating test, the amount of change in degree of polarization ΔP was determined using the following formula.
ΔP (%) = P ₄₈ −P ₀
The heating test was carried out by preparing a test sample in the same manner as in the case of color loss described above.

<Example 1>
1. 1. Fabrication of Laminate of Polarizer / Resin Base Material Amorphous isophthal copolymer polyethylene terephthalate film (thickness: 100 μm) as a resin base material, which is long, has a water absorption rate of 0.75%, and has a Tg of about 75 ° C. Was used. One side of the resin substrate was corona-treated.
100 weight of PVA-based resin in which polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "Gosefimer Z410") are mixed at a ratio of 9: 1. 13 parts by weight of potassium iodide was added to the part to prepare a PVA aqueous solution (coating liquid).
The PVA aqueous solution was applied to the corona-treated surface of the resin base material and dried at 60 ° C. to form a PVA-based resin layer having a thickness of 13 μm to prepare a laminate.
The obtained laminate was uniaxially stretched at the free end 2.4 times in the longitudinal direction (longitudinal direction) between rolls having different peripheral speeds in an oven at 130 ° C. (aerial auxiliary stretching treatment).
Next, the laminate was immersed in an insolubilizing bath at a liquid temperature of 40 ° C. (an aqueous boric acid solution obtained by blending 4 parts by weight of boric acid with 100 parts by weight of water) for 30 seconds (insolubilization treatment).
Next, in a dyeing bath having a liquid temperature of 30 ° C. (an aqueous iodine solution obtained by mixing iodine and potassium iodide in a weight ratio of 1: 7 with respect to 100 parts by weight of water), the polarizer finally obtained Immersion was carried out for 60 seconds while adjusting the concentration so that the simple substance transmittance (Ts) was 41.5% ± 0.1% (dyeing treatment).
Next, it was immersed in a cross-linked bath at a liquid temperature of 40 ° C. (an aqueous boric acid solution obtained by blending 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with respect to 100 parts by weight of water) for 30 seconds. (Crossing treatment).
Then, while immersing the laminate in a boric acid aqueous solution (boric acid concentration 4.0% by weight) at a liquid temperature of 70 ° C., the total draw ratio is 5.5 in the longitudinal direction (longitudinal direction) between rolls having different peripheral speeds. Uniaxial stretching was performed so as to double (underwater stretching treatment).
Then, the laminate was immersed in a washing bath at a liquid temperature of 20 ° C. (an aqueous solution obtained by blending 4 parts by weight of potassium iodide with 100 parts by weight of water) (cleaning treatment).
Then, while drying in an oven kept at 90 ° C., it was brought into contact with a heating roll made of SUS whose surface temperature was kept at 75 ° C. for about 2 seconds (dry shrinkage treatment). The shrinkage rate in the width direction of the laminated body by the drying shrinkage treatment was 5.2%.
In this way, a polarizer having a thickness of 5 μm was formed on the resin substrate to prepare a laminate of the polarizer / resin substrate. The simple substance transmittance (initial simple substance transmittance) Ts ₀ of the polarizer was 41.5, and the degree of polarization (initial polarization degree) P ₀ was 99.996%.

2. Preparation of Polarizing Plate A cycloolefin-based film (ZEON Corporation, ZT-12, thickness 23 μm) is applied to the surface of the polarizer obtained above as a film constituting the second protective layer, and an ultraviolet curable adhesive is applied. It was pasted together. Specifically, the curable adhesive was coated so as to have a total thickness of 1.0 μm, and bonded using a roll machine. Then, UV light was irradiated from the film side to cure the adhesive. Next, the resin base material was peeled off to obtain a polarizing plate having a second protective layer (ZT-12) / polarizer configuration.

20 parts of an acrylic resin (30 mol% lactone ring unit) which is a polymethyl methacrylate having a lactone ring unit was dissolved in 80 parts of methyl ethyl ketone to obtain an acrylic resin solution (20%). This acrylic resin solution is applied to the surface of the polarizer of the polarizing plate obtained above using a wire bar, and the coating film is dried at 60 ° C. for 5 minutes to form a solidified coating film. Protective layer was formed. The thickness of the first protective layer was 3 μm, the Tg was 119 ° C., and the iodine adsorption amount was 0.25% by weight. In this way, a polarizing plate having a structure of a first protective layer (solidified coating film) / polarizer / second protective layer (ZT-12) was obtained. The obtained polarizing plate was used for the evaluation of (3) and (4) above. Furthermore, the presence or absence of shrinkage after the formation of the protective layer was visually observed. The results are shown in Table 1.

<Example 2>
Same as Example 1 except that an acrylic resin (maleic anhydride unit 7 mol%) which is a polymethyl methacrylate having a maleic anhydride unit was used instead of the acrylic resin which is a polymethyl methacrylate having a lactone ring unit. The first protective layer was formed. The thickness of the first protective layer was 3 μm, and the Tg was 115 ° C. A polarizing plate was produced in the same manner as in Example 1 except that the first protective layer was used. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

<Example 3>
Example 1 and Example 1 except that an acrylic resin (manufactured by Kusumoto Kasei Co., Ltd., product name “B-728”) which is 100% polymethylmethacrylate is used instead of the acrylic resin which is polymethylmethacrylate having a lactone ring unit. A first protective layer was formed in the same manner. The thickness of the first protective layer was 3 μm, the Tg was 116 ° C., and the iodine adsorption amount was 0.34% by weight. A polarizing plate was produced in the same manner as in Example 1 except that the first protective layer was used. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

<Example 4>
Same as Example 1 except that an acrylic resin (glutarimide ring unit 4 mol%) which is a polymethyl methacrylate having a glutarimide ring unit was used instead of the acrylic resin which is a polymethyl methacrylate having a lactone ring unit. The first protective layer was formed. The thickness of the first protective layer was 3 μm, the Tg was 103 ° C., and the iodine adsorption amount was 2.3% by weight. A polarizing plate was produced in the same manner as in Example 1 except that the first protective layer was used. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

<Example 5>
The first protective layer was formed in the same manner as in Example 1 except that an acrylic resin (20 mol% lactone ring unit), which is a different polymethyl methacrylate having a lactone ring unit, was used. The thickness of the first protective layer was 3 μm, the Tg was 104 ° C., and the iodine adsorption amount was 2.8% by weight. A polarizing plate was produced in the same manner as in Example 1 except that the first protective layer was used. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

<Example 6>
The same as in Example 1 except that an acrylic resin which is a copolymer of methyl methacrylate / butyl methacrylate (molar ratio 80/20) was used instead of the acrylic resin which is a polymethyl methacrylate having a lactone ring unit. A first protective layer was formed. The thickness of the first protective layer was 3 μm, the Tg was 95 ° C., and the iodine adsorption amount was 3.8% by weight. A polarizing plate was produced in the same manner as in Example 1 except that the first protective layer was used. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

<Comparative example 1>
Acrylic resin (manufactured by Kusumoto Kasei Co., Ltd., product name "B-722") which is a copolymer of methyl methacrylate / ethyl acrylate (molar ratio 55/45) instead of acrylic resin which is polymethyl methacrylate having a lactone ring unit. ) Was used, and the first protective layer was formed in the same manner as in Example 1. The thickness of the first protective layer was 3 μm, the Tg was 39 ° C., and the iodine adsorption amount was 1.7% by weight. A polarizing plate was produced in the same manner as in Example 1 except that the first protective layer was used. When the obtained polarizing plate was used for evaluation of color loss, it was defective (“total loss”), so the single transmittance and the degree of polarization were not evaluated. The results are shown in Table 1.

<Comparative example 2>
Acrylic resin (manufactured by Kusumoto Kasei Co., Ltd., product name "B-734") which is a copolymer of methyl methacrylate / butyl methacrylate (molar ratio 35/65) instead of acrylic resin which is polymethyl methacrylate having a lactone ring unit. ) Was used, and the first protective layer was formed in the same manner as in Example 1. The thickness of the first protective layer was 3 μm, the Tg was 71 ° C., and the iodine adsorption amount was 12% by weight. A polarizing plate was produced in the same manner as in Example 1 except that the first protective layer was used. When the obtained polarizing plate was used for evaluation of color loss, it was defective (“total loss”), so the single transmittance and the degree of polarization were not evaluated. The results are shown in Table 1.

<Comparative example 3>
The first protective layer is the same as in Example 1 except that an ultraviolet curable acrylic resin (manufactured by Kyoeisha Chemical Co., Ltd., product name "Light Acrylate HPP-A", neopentyl glycol acrylic acid adduct of hydroxypivalate) is used. A (cured product) was formed. Specifically, a composition containing 97% by weight of the acrylic resin and 3% by weight of a photopolymerization initiator (Irgacure 907, manufactured by BASF) is applied onto a polarizer, and a high-pressure mercury lamp is used in a nitrogen atmosphere. The cured layer (first protective layer) was formed by irradiating ultraviolet rays with an integrated light amount of 300 mJ / cm ^2. The thickness of the first protective layer was 3 μm, the Tg was 83 ° C., and the iodine adsorption amount was 6.6% by weight. A polarizing plate was produced in the same manner as in Example 1 except that the first protective layer was used. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

<Comparative example 4>
Same as Example 1 except that an ultraviolet curable acrylic resin (manufactured by Toagosei Co., Ltd., product name "Aronix M-402", dipentaerythritol penta and hexaacrylate (pentaacrylate is 30% to 40%)) is used. The first protective layer (cured product) was formed. The method for forming the first protective layer was the same as in Comparative Example 3. The thickness of the first protective layer was 3 μm. A polarizing plate was produced in the same manner as in Example 1 except that the first protective layer was used. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

<Comparative example 5>
A first protective layer (cured product) was formed in the same manner as in Example 1 except that an ultraviolet curable epoxy resin (manufactured by Daicel Corporation, product name “Ceroxide 2021P”) was used. Specifically, a composition containing 95% by weight of the epoxy resin and 5% by weight of a photopolymerization initiator (CPI-100P, manufactured by San-Apro) is applied onto a polarizer, and a high-pressure mercury lamp is used in an air atmosphere. The cured layer (first protective layer) was formed by irradiating ultraviolet rays with an integrated light amount of 500 mJ / cm ^2. The thickness of the first protective layer was 3 μm, the Tg was 95 ° C., and the iodine adsorption amount was 9% by weight. A polarizing plate was produced in the same manner as in Example 1 except that the first protective layer was used. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

<Comparative Example 6>
A first protective layer (solidified coating film) was formed in the same manner as in Example 1 except that an aqueous polyester resin (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., product name “Polyester WR905”) was used. The thickness of the first protective layer was 3 μm, and the amount of iodine adsorbed was 12% by weight. A polarizing plate was produced in the same manner as in Example 1 except that the first protective layer was used. When the obtained polarizing plate was used for evaluation of color loss, it was defective (“total loss”), so the single transmittance and the degree of polarization were not evaluated. The results are shown in Table 1.

<Comparative Example 7>
A first protective layer (solidified coating film) was formed in the same manner as in Example 1 except that an aqueous polyurethane resin (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., product name "Superflex SF210") was used. The thickness of the first protective layer was 3 μm, the Tg was 107 ° C., and the iodine adsorption amount was 19% by weight. A polarizing plate was produced in the same manner as in Example 1 except that the first protective layer was used. When the obtained polarizing plate was used for evaluation of color loss, it was defective (“total loss”), so the single transmittance and the degree of polarization were not evaluated. The results are shown in Table 1.

<Comparative Example 8>
A first protective layer (solidified coating film) was formed in the same manner as in Example 1 except that an aqueous polyurethane resin (manufactured by Unitika Ltd., product name “Arrow Base SE1200”) was used. The thickness of the first protective layer was 3 μm, and the amount of iodine adsorbed was 15% by weight. A polarizing plate was produced in the same manner as in Example 1 except that the first protective layer was used. When the obtained polarizing plate was used for evaluation of color loss, it was defective (“total loss”), so the single transmittance and the degree of polarization were not evaluated. The results are shown in Table 1.

<Evaluation>
As is clear from Table 1, although the polarizing plate of the embodiment of the present invention is very thin, deterioration of optical characteristics is suppressed even in a heating and humidifying environment, and it is excellent in durability and a protective layer. It is a polarizing plate that does not shrink after formation and can withstand practical use.

The polarizing plate of the present invention is suitably used for an image display device. Examples of image display devices include portable devices such as mobile information terminals (PDAs), smartphones, mobile phones, clocks, digital cameras, and portable game machines; OA devices such as personal computer monitors, laptop computers, and copiers; video cameras and televisions. , Home appliances such as microwave ovens; Back monitors, car navigation system monitors, car audio and other in-vehicle devices; Digital signage, commercial store information monitors and other exhibition devices; Surveillance monitors and other security devices; Nursing care Nursing care / medical equipment such as monitors for medical use and monitors for medical use;

10 Polarizer 20 First protective layer 30 Second protective layer 100 Polarizing plate

Claims (8)

It has a polarizer, a first protective layer arranged on one side of the polarizer, and a second protective layer arranged on the other side of the polarizer.
The first protective layer is composed of a solidified coating film of an organic solvent solution of a thermoplastic acrylic resin, and the glass transition temperature of the first protective layer is 95 ° C. or higher.
The second protective layer is made of a resin film.
Polarizer. The polarizing plate according to claim 1, wherein the thickness of the first protective layer is 10 μm or less. The polarizing plate according to claim 1 or 2, wherein the iodine adsorption amount of the first protective layer is 4.0% by weight or less. One of claims 1 to 3, wherein the thermoplastic acrylic resin has at least one selected from the group consisting of a lactone ring unit, a glutaric anhydride unit, a glutarimide unit, a maleic anhydride unit, and a maleimide unit. The polarizing plate according to the description. The aspect according to any one of claims 1 to 4, wherein the in-plane retardation Re (550) of the first protective layer is 0 nm to 10 nm, and the retardation Rth (550) in the thickness direction is −20 nm to +10 nm. Polarizer. The polarizing plate according to any one of claims 1 to 5, wherein the first protective layer is arranged on the display cell side of the image display device, and the second protective layer is arranged on the opposite side of the display cell. The polarizing plate according to claim 6, which is arranged on the visual side of the image display device. A polarizing plate roll in which the polarizing plate according to any one of claims 1 to 7 is wound in a roll shape.

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