JP5945037B2 - Polarizer - Google Patents

Description

  The present invention relates to a polarizing plate including a polarizer in which iodine is adsorbed and oriented on a polyvinyl alcohol resin layer.

  The polarizing plate has been widely used in display devices such as liquid crystal display devices, particularly in recent years, various mobile devices such as smartphones and slate PCs. With the development of mobile devices, there is an increasing demand for thinner and lighter polarizing plates, and on the other hand, excellent heat resistance is also required.

  However, when a conventional polarizing plate is subjected to a heat resistance test (usually 500 to 750 hours at 80 to 85 ° C.), the red light leaks from the polarizing plate, causing a problem of “red change” or having a large degree of polarization. There was a tendency to decrease. For example, as a method for suppressing reddening, a method in which a polarizer contains zinc ions is known (for example, Patent Documents 1 and 2). However, this method has problems that zinc is deposited on the surface of the polarizer, that the concentration control of zinc is complicated, and that the drug used has skin irritation.

Japanese Patent Publication No. 60-033245 Japanese Examined Patent Publication No. 02-034001

  An object of this invention is to provide the polarizing plate excellent in heat resistance which does not produce a red discoloration and a polarization degree fall by a heat test.

The present invention provides the following polarizing plate.
[1] A polarizer in which iodine is adsorbed and oriented in the polyvinyl alcohol-based resin layer,
The phase difference value R _{i of} iodine is 160 nm or more,
The single transmittance Ty is 41 to 43%, the degree of polarization Py is 99.9% or more, and the ratio T ₄₀₀ / T between the orthogonal transmittance T ₄₀₀ at a wavelength of ₄₀₀ nm and the orthogonal transmittance T ₇₀₀ at a wavelength of 700 nm. _A polarizing plate in which ₇₀₀ is 0.5 or more.

[2] The polarizing plate according to [1], wherein the b value of the orthogonal hue is −2.5 to −0.5.
[3] The polarizing plate according to [1] or [2], wherein a change rate of the degree of polarization before and after a heat resistance test heated at 85 ° C. for 500 hours is 0.05% or less.

  [4] The polarizing plate according to any one of [1] to [3], wherein the polarizer has a thickness of 15 μm or less.

  [5] The polarizing plate according to any one of [1] to [4], further including a protective film laminated on at least one surface of the polarizer.

  According to the polarizing plate of the present invention, redness and a decrease in the degree of polarization due to a heat resistance test can be suppressed.

It is a schematic sectional drawing which shows an example of the laminated constitution of the polarizing plate which concerns on this invention. It is a schematic sectional drawing which shows another example of the laminated constitution of the polarizing plate which concerns on this invention.

(1) Configuration of Polarizing Plate FIG. 1 is a schematic sectional view showing an example of a layer configuration of a polarizing plate according to the present invention. Like the polarizing plate 1 shown in FIG. 1, the polarizing plate of the present invention includes a polarizer 5, a first protective film 10 laminated on one surface of the polarizer 5 with a first adhesive layer 15, and the other surface. It can be a polarizing plate with a double-sided protective film comprising the second protective film 20 laminated on the second adhesive layer 25. The polarizing plate 1 may further have another optical layer, an adhesive layer, or the like laminated on the first protective film 10 and / or the second protective film 20.

  Moreover, the polarizing plate of this invention is equipped with the polarizer 5 and the 1st protective film 10 laminated | stacked on the one surface through the 1st adhesive bond layer 15 like the polarizing plate 2 shown by FIG. A polarizing plate with a single-sided protective film may be used. The polarizing plate 2 may further include another optical layer (or optical film) or an adhesive layer that is laminated on the first protective film 10 and / or the polarizer 5.

  As another optical layer (or optical film), a reflective polarizing film that transmits a certain kind of polarized light and reflects polarized light that exhibits the opposite properties; a film with an anti-glare function having an uneven shape on the surface; surface Examples thereof include a film with an antireflection function; a reflection film having a reflection function on the surface; a transflective film having both a reflection function and a transmission function; and a viewing angle compensation film.

(2) Optical properties of polarizing plate Polarizing plates 1 and 2 according to the present invention have the following optical properties:
[A] In the polarizing plates 1 and 2, the iodine phase difference value R _i is 160 nm or more.
[B] The single transmittance Ty is 41 to 43%.
[C] The degree of polarization Py is 99.9% or more, and [d] The ratio T ₄₀₀ / T ₇₀₀ between the orthogonal transmittance T ₄₀₀ at a wavelength of ₄₀₀ nm and the orthogonal transmittance T ₇₀₀ at a wavelength of 700 nm is 0.5. The polarizing plate satisfies the above, preferably 0.9 or more. These optical properties are all before the heat resistance test. In addition, as will be described in detail in the section of the following examples, the single transmittance, the polarization degree, and the orthogonal transmittance in the present specification are corrected for visibility.

  The polarization performance of the polarizing plate can be mainly expressed by the single transmittance Ty and the polarization degree Py. In order to ensure good image clarity when the polarizing plate is applied to a display device such as a liquid crystal display device, the polarizing plates 1 and 2 preferably have a single transmittance Ty of 40% or more. % Or more, and the degree of polarization Py is preferably 99% or more, and more preferably 99.9% or more.

  Various studies are conducted to improve the heat resistance of the polarizing plate (reduces redness and decrease in the degree of polarization), and on the premise that good polarization performance can be maintained to satisfy the above [b] and [c]. It was found that the polarizing plates 1 and 2 satisfying both the above [a] and [d] can improve the heat resistance. When the thickness of the polarizer 5 is as small as 15 μm or less, redness and a decrease in the degree of polarization are likely to occur, but the polarizing plates 1 and 2 satisfying the above [a] to [d] have excellent polarization characteristics. High heat resistance while having. Such high heat resistance lasts for a long period of time even when the polarizing plates 1 and 2 are applied to a display device such as a liquid crystal display device and are put into actual use.

Retardation value R _i of the iodine in the [a] is a retardation value at a wavelength of 1000 nm, a characteristic value serving as an index indicating the orientation of the iodine. In the present invention, this is increased to 160 nm or more. That the R _i and 160nm or more is particularly advantageous in suppressing a decrease in the polarization degree under heat resistance test. When R _i is less than 160 nm, it is difficult to obtain excellent heat resistance even when satisfying the above [d]. R _i is preferably 165 nm or more, and more preferably 170 nm or more. R _i is usually 280 nm or less, preferably 250 nm or less, more preferably 220 nm or less. A method for measuring the like of the retardation value R _i of iodine, according to the description of the Examples section below.

When R _i is obtained in accordance with the description in the section of the embodiment below, the wavelength when the actually measured retardation value R (λ) of the polarizer 5 is separated into a term having wavelength dependence and a term having no wavelength dependence. As a term having no dependency, the retardation value R _pva of the polyvinyl alcohol resin is also obtained. Term having a wavelength dependency is R _i. The retardation value R _pva of the polyvinyl alcohol resin is a characteristic value serving as an index indicating the orientation of the polyvinyl alcohol resin constituting the polarizer 5. R _pva is usually in the range of about 250 to 450 nm (for example, about 300 to 400 nm).

From the viewpoint of improving the heat resistance of the polarizing plates 1 and 2, the ratio R _i / R _pva between the retardation value R _{i of} iodine and the retardation value R _pva of the polyvinyl alcohol resin is preferably 0.30 or more, More preferably, it is 0.32 or more, More preferably, it is 0.35 or more. The upper limit of the R _i / R _pva is not particularly limited, R _i / R _pva may be, for example, less than 0.38.

In order to obtain excellent heat resistance, the ratio T ₄₀₀ / T ₇₀₀ between the orthogonal transmittance T ₄₀₀ at a wavelength of ₄₀₀ nm and the orthogonal transmittance T ₇₀₀ at a wavelength of 700 nm is 0.5 or more as described in [d] above. Preferably, it should be 0.9 or more. T ₄₀₀ / T ₇₀₀ may be 0.7 or more, 0.9 or more, 1 or more, and may be 1.5 or more. Setting T ₄₀₀ / T ₇₀₀ to 0.5 or more, particularly 0.9 or more is particularly advantageous for suppressing red discoloration under the heat resistance test. T ₇₀₀ of the polarizing plate corresponds to the orthogonal transmittance at the base of the absorption band on the long wavelength side (red region), and T ₄₀₀ corresponds to the orthogonal transmittance at the base of the absorption band on the short wavelength side (blue region). However, the present inventor can evaluate the intensity of the absorption band on the long wavelength side and the short wavelength side before the heat test by T ₇₀₀ and T ₄₀₀ , respectively, and in the polarizing plate as an alternative evaluation physical property of such absorption band intensity. Using T ₇₀₀ and T ₄₀₀ , finding that the ratio T ₄₀₀ / T ₇₀₀ is 0.5 or more, preferably 0.9 or more is advantageous for improving heat resistance, especially for suppressing redness. It is. When T ₄₀₀ / T ₇₀₀ is less than 0.9, particularly less than 0.5, it is difficult to obtain excellent heat resistance even when the above [a] is satisfied. T ₄₀₀ / T ₇₀₀ is usually 30 or less. About the measuring method of _T400 / _T700 , it follows the description of the term of the following Example.

T ₄₀₀ can usually be in the range of about 0.0003 to 0.3%, for example, about 0.0005 to 0.2%. T ₇₀₀ can also be in the range of usually about 0.0003 to 0.3%, for example about 0.0005 to 0.2%.

  The polarizing plates 1 and 2 according to the present invention exhibit excellent polarization performance with a single transmittance Ty of 41 to 43% and a polarization degree Py of 99.9% or more. If the single transmittance Ty is high, redness tends to occur. However, according to the present invention, even in such a case, for example, even if the single transmittance Ty is about 42% or more, the heat resistance is excellent. The polarizing plates 1 and 2 can be provided. Moreover, the polarizing plates 1 and 2 having a single transmittance Ty of 43% or less, preferably 42.8% or less are advantageous in that the degree of polarization after the heat test is maintained high. About the measuring method of Ty and Py, it follows description of the term of the following Example.

  The polarizing plates 1 and 2 according to the present invention are excellent in heat resistance, and the decrease in the degree of polarization Py by a heat test (usually 500 to 750 hours at 80 to 85 ° C.) is small. According to the present invention, the change rate Z of the degree of polarization before and after the heat resistance test defined by the formulas described in the Examples section below is 0.05% or less, further 0.04% or less, and even more preferably 0.03. % Or less of polarizing plates 1 and 2 can be provided.

  In the polarizing plates 1 and 2 according to the present invention, the b value of the orthogonal hue measured in accordance with the description in the Examples below is preferably in the range of −2.5 to −0.5, and −2.0 More preferably within the range of -0.6. The polarizing plates 1 and 2 having the b value of the orthogonal hue within this range are advantageous in that red discoloration is more effectively suppressed and the black display in the initial state is kept near the neutral.

(3) Polarizer As the polarizer 5, a polyvinyl alcohol resin layer in which iodine is adsorbed and oriented is used. Examples of such a polarizer include a step of uniaxially stretching a polyvinyl alcohol-based resin film; a step of adsorbing iodine by dyeing the polyvinyl alcohol-based resin film with iodine; a polyvinyl alcohol-based resin film on which iodine is adsorbed; A polarizing film that can be produced by a method including a step of treating with an aqueous acid solution; and a step of washing with water after the treatment with an aqueous boric acid solution can be used.

  As the polyvinyl alcohol resin, a saponified polyvinyl acetate resin can be used. Examples of the polyvinyl acetate resin include, in addition to polyvinyl acetate, which is a homopolymer of vinyl acetate, copolymers with other monomers copolymerizable with vinyl acetate. Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, (meth) acrylamides having ammonium groups, and the like. In the present specification, “(meth) acryl” means at least one selected from acryl and methacryl. The same applies to “(meth) acryloyl”.

  The saponification degree of the polyvinyl alcohol resin is usually about 85 to 100 mol%, preferably 98 mol% or more. The polyvinyl alcohol-based resin may be modified, and for example, polyvinyl formal or polyvinyl acetal modified with aldehydes may be used. The average degree of polymerization of the polyvinyl alcohol-based resin is usually about 1000 to 10000, preferably about 1500 to 5000, and more preferably about 1500 to 4000. The average degree of polymerization of the polyvinyl alcohol resin can be determined according to JIS K 6726.

  What formed such a polyvinyl alcohol-type resin into a film is used as a raw film of the polarizer 5 (polarizing film). The method for forming the polyvinyl alcohol-based resin into a film is not particularly limited, and a known method is employed. The film thickness of the polyvinyl alcohol-based raw film is, for example, about 10 to 150 μm.

  Uniaxial stretching of the polyvinyl alcohol-based resin film can be performed before dyeing iodine, simultaneously with dyeing, or after dyeing. When uniaxial stretching is performed after dyeing, this uniaxial stretching may be performed before boric acid treatment or during boric acid treatment. Moreover, you may uniaxially stretch in these several steps.

  In uniaxial stretching, it may be uniaxially stretched between rolls having different peripheral speeds, or may be uniaxially stretched using a hot roll. The uniaxial stretching may be dry stretching in which stretching is performed in the air, or may be wet stretching in which stretching is performed in a state where a polyvinyl alcohol-based resin film is swollen using a solvent. The draw ratio is usually about 3 to 8 times.

  As a method of dyeing the polyvinyl alcohol resin film with iodine, for example, a method of immersing the polyvinyl alcohol resin film in an aqueous solution (dye bath) containing iodine is employed. In addition, it is preferable that the polyvinyl alcohol-type resin film performs the immersion process to water before a dyeing process.

  As the dyeing treatment with iodine, a method of immersing a polyvinyl alcohol resin film in a dyeing bath containing iodine and potassium iodide is usually employed. The iodine content in this dyeing bath can be about 0.01 to 1 part by weight per 100 parts by weight of water. The content of potassium iodide can be about 0.5 to 20 parts by weight per 100 parts by weight of water. The temperature of the dyeing bath can be about 20 to 40 ° C.

  As the boric acid treatment after dyeing with iodine, a method of immersing the dyed polyvinyl alcohol-based resin film in a boric acid-containing aqueous solution (crosslinking bath) is usually employed. This crosslinking bath preferably contains potassium iodide. The amount of boric acid in the crosslinking bath can be about 2 to 15 parts by weight per 100 parts by weight of water, and the amount of potassium iodide can be about 0.1 to 15 parts by weight per 100 parts by weight of water. it can. The temperature of the crosslinking bath can be 50 ° C. or higher, for example, 50 to 85 ° C.

  The polyvinyl alcohol resin film after the boric acid treatment is usually washed with water. The water washing treatment can be performed, for example, by immersing a boric acid-treated polyvinyl alcohol resin film in water. The temperature of water in the water washing treatment is usually about 5 to 40 ° C. The immersion time is usually about 1 to 120 seconds.

  A polarizer 5 is obtained by performing a drying process after washing with water. The drying process can be performed using a hot air dryer or a far infrared heater. The thickness of the polarizer 5 is preferably 15 μm or less, and more preferably 10 μm or less. While it is possible to reduce the thickness of the polarizing plates 1 and 2 by setting the thickness of the polarizer 5 to 15 μm or less, according to the present invention, even when such a thin film polarizer 5 is used, It is possible to effectively suppress reddening and a decrease in the degree of polarization. The thickness of the polarizer 5 is usually 5 μm or more.

(4) First and second protective films The first and second protective films 10 and 20 each have a translucent (preferably optically transparent) thermoplastic resin such as a chain polyolefin resin (polypropylene). Polyolefin resins such as cyclic polyolefin resins (norbornene resins, etc.); cellulose ester resins such as triacetyl cellulose and diacetyl cellulose; polyester resins; polycarbonate resins; (meth) acrylic resins Polystyrene film; or a film made of a mixture or copolymer thereof. The first protective film 10 and the second protective film 20 may be the same type of protective film or different types of protective films.

  The 1st and / or 2nd protective films 10 and 20 can also be protective films which have optical functions like a phase difference film and a brightness improvement film. For example, a retardation film provided with an arbitrary retardation value by stretching a film made of the thermoplastic resin (uniaxial stretching or biaxial stretching) or by forming a liquid crystal layer or the like on the film. It can be.

  Examples of the chain polyolefin-based resin include a homopolymer of a chain olefin such as a polyethylene resin and a polypropylene resin, and a copolymer composed of two or more chain olefins.

  Cyclic polyolefin resin is a general term for resins that are polymerized using a cyclic olefin as a polymerization unit. Specific examples of cyclic polyolefin resins include ring-opening (co) polymers of cyclic olefins, addition polymers of cyclic olefins, copolymers of cyclic olefins and chain olefins such as ethylene and propylene (typically Are random copolymers), graft polymers obtained by modifying them with unsaturated carboxylic acids or derivatives thereof, and hydrides thereof. Among these, norbornene resins using norbornene monomers such as norbornene and polycyclic norbornene monomers as cyclic olefins are preferably used.

  The cellulose ester resin is an ester of cellulose and a fatty acid. Specific examples of the cellulose ester-based resin include triacetyl cellulose (TAC) and diacetyl cellulose. Moreover, these copolymers and those in which a part of the hydroxyl group is modified with other substituents can also be used. Of these, TAC is particularly preferred.

  The polyester-based resin is a resin having an ester bond other than the cellulose ester-based resin, and generally includes a polycondensate of a polyvalent carboxylic acid or a derivative thereof and a polyhydric alcohol. As the polyvalent carboxylic acid or a derivative thereof, a dicarboxylic acid or a derivative thereof can be used, and examples thereof include terephthalic acid, isophthalic acid, dimethyl terephthalate, and dimethyl naphthalenedicarboxylate. A diol can be used as the polyhydric alcohol, and examples thereof include ethylene glycol, propanediol, butanediol, neopentyl glycol, and cyclohexanedimethanol.

  Specific examples of the polyester resin include polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polytrimethylene terephthalate, polytrimethylene naphthalate, polycyclohexanedimethyl terephthalate, and polycyclohexanedimethyl naphthalate.

  The polycarbonate resin is composed of a polymer in which monomer units are bonded via a carbonate group. The polycarbonate-based resin may be a resin called a modified polycarbonate having a modified polymer skeleton, a copolymer polycarbonate, or the like.

The (meth) acrylic resin is a resin containing a compound having a (meth) acryloyl group as a main constituent monomer. Specific examples of (meth) acrylic resins include, for example, poly (meth) acrylic acid esters such as polymethyl methacrylate; methyl methacrylate- (meth) acrylic acid copolymer; methyl methacrylate- (meth) acrylic acid Ester copolymer; methyl methacrylate-acrylic ester- (meth) acrylic acid copolymer; (meth) methyl acrylate-styrene copolymer (MS resin etc.); methyl methacrylate and alicyclic hydrocarbon group And a copolymer (for example, methyl methacrylate-cyclohexyl methacrylate copolymer, methyl methacrylate- (meth) acrylate norbornyl copolymer). Preferably, a polymer based on a poly (meth) acrylic acid C _1-6 alkyl ester such as poly (meth) acrylic acid methyl is used, and more preferably methyl methacrylate is the main component (50-100). % Methyl methacrylate resin is used.

  Surface treatment layers such as a hard coat layer, an antiglare layer, an antireflection layer, an antistatic layer, and an antifouling layer are provided on the surface of the first and / or second protective film 10, 20 opposite to the polarizer 5. (Coating layer) can also be formed.

  The thickness of the first and second protective films 10 and 20 is preferably 90 μm or less, more preferably 50 μm or less, and even more preferably 40 μm or less, from the viewpoint of reducing the thickness of the polarizing plates 1 and 2. The thickness is usually 5 μm or more from the viewpoint of strength and handleability.

(5) First and second adhesive layers As the adhesive forming the first and second adhesive layers 15 and 25, a water-based adhesive or an active energy ray-curable adhesive can be used. The adhesive that forms the first adhesive layer 15 and the adhesive that forms the second adhesive layer 25 may be the same or different.

  Examples of the water-based adhesive include an adhesive made of a polyvinyl alcohol-based resin aqueous solution, an aqueous two-component urethane emulsion adhesive, and the like. Among these, a water-based adhesive composed of a polyvinyl alcohol-based resin aqueous solution is preferably used.

  Polyvinyl alcohol resins include vinyl alcohol homopolymers obtained by saponifying polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable therewith. A polyvinyl alcohol copolymer obtained by saponifying a polymer, or a modified polyvinyl alcohol polymer obtained by partially modifying the hydroxyl group thereof can be used. The water-based adhesive can contain additives such as polyvalent aldehydes, water-soluble epoxy compounds, melamine compounds, zirconia compounds, and zinc compounds.

  When using a water-based adhesive, it is preferable to carry out a drying step for removing the water contained in the water-based adhesive after bonding the polarizer 5 and the protective film. After the drying process, for example, a curing process for curing at a temperature of about 20 to 45 ° C. may be provided.

  The active energy ray-curable adhesive refers to an adhesive that cures when irradiated with active energy rays such as ultraviolet rays. For example, the active energy ray-curable adhesive includes a polymerizable compound and a photopolymerization initiator, and includes a photoreactive resin. And those containing a binder resin and a photoreactive cross-linking agent. Examples of the polymerizable compound include photopolymerizable monomers such as photocurable epoxy monomers, photocurable (meth) acrylic monomers, and photocurable urethane monomers, and oligomers derived from the photopolymerizable monomers. it can. Examples of the photopolymerization initiator include those containing substances that generate active species such as neutral radicals, anion radicals, and cation radicals upon irradiation with active energy rays such as ultraviolet rays. As the active energy ray-curable adhesive containing a polymerizable compound and a photopolymerization initiator, those containing a photocurable epoxy monomer and a cationic photopolymerization initiator can be preferably used.

  When using an active energy ray-curable adhesive, after bonding the polarizer 5 and the protective film, a drying process is performed as necessary, and then the active energy ray-curable adhesive is irradiated by irradiating active energy rays. A curing step is performed to cure. The light source of the active energy ray is not particularly limited, but ultraviolet light having a light emission distribution at a wavelength of 400 nm or less is preferable. A wave excitation mercury lamp, a metal halide lamp, etc. can be used.

(6) Adhesive layer On the first protective film 10 or the second protective film 20 in the polarizing plate 1 shown in FIG. 1 and on the polarizer 5 in the polarizing plate 2 shown in FIG. For example, you may laminate | stack the adhesive layer for bonding to the liquid crystal cell in the case of applying to a liquid crystal display device. The pressure-sensitive adhesive forming the pressure-sensitive adhesive layer is usually based on a (meth) acrylic resin, styrene resin, silicone resin or the like, and a crosslinking agent such as an isocyanate compound, an epoxy compound, or an aziridine compound is added thereto. It consists of an adhesive composition. Furthermore, it can also be set as the adhesive layer which contains microparticles | fine-particles and shows light-scattering property. The thickness of the pressure-sensitive adhesive layer can be 1 to 40 μm, but it is preferably formed thin as long as the workability and durability characteristics are not impaired, and specifically, it is preferably 3 to 25 μm.

  The method of forming the pressure-sensitive adhesive layer is not particularly limited, and a pressure-sensitive adhesive composition (pressure-sensitive adhesive solution) containing each component including the above-mentioned base polymer is applied to the protective film surface or the polarizer surface. The pressure-sensitive adhesive layer may be formed by drying, or after the pressure-sensitive adhesive layer is formed on the separator (release film), the pressure-sensitive adhesive layer may be transferred to the protective film surface or the polarizing film surface. When forming the pressure-sensitive adhesive layer on the protective film surface or the polarizer surface, the protective film surface or the polarizer surface, or one or both surfaces of the pressure-sensitive adhesive layer may be subjected to a surface treatment such as corona treatment, if necessary. Good.

(7) Manufacturing method of polarizing plate The single side | surface shown by FIG. 2 by bonding the 1st protective film 10 according to a conventional method through the 1st adhesive bond layer 15 to the single side | surface of the above-mentioned polarizer 5 (polarizing film). The polarizing plate 2 with a protective film can be obtained. If the 2nd protective film 20 is bonded to the other surface of the polarizer 5 through the 2nd adhesive bond layer 25, the polarizing plate 1 with a double-sided protective film shown by FIG. 1 will be obtained. When obtaining the polarizing plate 1 with a double-sided protective film, the 1st and 2nd protective films 10 and 20 may be bonded simultaneously, and may be bonded sequentially.

Not only the method of bonding a protective film to a polarizer 5 made of a single (single) film, but also a polarizing plate is produced using a polyvinyl alcohol resin layer and a base film for supporting the polarizer in the manufacturing process. May be. This method is described in, for example, Japanese Patent Application Laid-Open No. 2012-103466. In this case, the polarizing plate 2 with a single-sided protective film is, for example, the following process:
After applying a coating liquid containing a polyvinyl alcohol-based resin on at least one surface of the base film, a resin layer forming step of forming a polyvinyl alcohol-based resin layer by drying to obtain a laminated film,
Stretching process for obtaining a stretched film by uniaxially stretching the laminated film,
A dyeing step of obtaining a polarizing laminated film by dyeing the polyvinyl alcohol resin layer of the stretched film with iodine to form a polarizer 5;
The 1st bonding process of bonding the 1st protective film 10 on the polarizer 5 of a light-polarizing laminated film, and obtaining the bonding film,
It can manufacture by the method of peeling and removing a base film from a bonding film, and obtaining the polarizing plate 2 with a single-sided protective film in this order.

When the polarizing plate 1 with a double-sided protective film shown in FIG. 1 is produced, the second protective film 20 is further bonded to the surface on the polarizer 5 side of the polarizing plate 2 with a single-sided protective film after the peeling step. A 2nd bonding process is included.

A specific method for adjusting various optical characteristics of the polarizing plates 1 and 2 within the predetermined or preferable numerical range will be described below. There are several factors that affect the orthogonal transmittances T ₄₀₀ and T ₇₀₀ and their ratio T ₄₀₀ / T ₇₀₀ , as well as the single transmittance, the degree of polarization, the retardation value R _{i of} iodine and the b value of the orthogonal hue, Specific examples of the main factors are as follows.

1) Iodine concentration in dyeing bath used for dyeing treatment,
2) Potassium iodide concentration of the crosslinking bath used for boric acid treatment, and immersion time in the crosslinking bath,
3) Polyvinyl alcohol-based resin layer or film stretch ratio, neck-in ratio during stretching, and stretching temperature,
4) Water washing temperature in water washing treatment after boric acid treatment, and immersion time in water,
5) Drying temperature and drying time in the drying process after the water washing process,
6) Final neck-in rate after the polyvinyl alcohol-based resin layer or film is subjected to dyeing treatment, boric acid treatment, water washing treatment and drying treatment.

Above all, 2) has a great influence on the orthogonal transmittance ratio T ₄₀₀ / T ₇₀₀ . In order to set the orthogonal transmittance ratio T ₄₀₀ / T ₇₀₀ of the polarizing plates 1 and 2 to 0.5 or more, preferably 0.9 or more, the potassium iodide concentration of the crosslinking bath is 12 parts by weight or less per 100 parts by weight of water. The immersion time in the crosslinking bath is preferably adjusted as appropriate, preferably 10 parts by weight or less, more preferably adjusted in the crosslinking bath as appropriate, and the potassium iodide concentration in the crosslinking bath is 9 parts by weight or less. More preferably, the immersion time in the crosslinking bath is appropriately adjusted. Moreover, it is preferable that the potassium iodide density | concentration of a crosslinking bath shall be 7 weight part or more per 100 weight part of water.

The phase difference value R _i of iodine is particularly affected by 3) and 6). The R _i to a 160nm or more, the draw ratio, the neck-in rate at the time of stretching, it is preferable to increase the stretching temperature, and / or final neck-in ratio. In order to increase the degree of polarization, it is preferable to increase the draw ratio. When the draw ratio is low, the orientation is insufficient and it is difficult to obtain a polarizer having high polarization performance (polarization degree). On the other hand, when the draw ratio is too high, the stretch breakage tends to occur, and the polarizer becomes too thin, and the workability in the subsequent process may be lowered. In order to increase the neck-in rate, it is preferable to increase the dyeing temperature or the boric acid treatment temperature. The final neck-in ratio is expressed by the following formula when the width of the unstretched polyvinyl alcohol-based resin layer or film is W ₀ (mm) and the width of the polarizer after the drying treatment is W ₁ :
Neck-in rate (%) = 100 × (W ₀ −W ₁ ) / W ₀
It is represented by Neck-in ratio at the time of stretching refers to the above-mentioned “width of unstretched polyvinyl alcohol-based resin layer or film” as “width of polyvinyl alcohol-based resin layer or film before stretching”, and “width of polarizer after drying treatment” "Is replaced with" width of the stretched polyvinyl alcohol-based resin layer or film "and calculated based on the above formula.

Regarding the above 4), as the washing temperature in the washing treatment is higher and the immersion time in water is longer, the orthogonal transmittance ratio T ₄₀₀ / T ₇₀₀ tends to be 0.5 or more, more preferably 0.9 or more. is there.

Taking into account the guidelines described above, 1) while controlling the conditions of 6), crossed transmittance T _400, T ₇₀₀ and their ratio T ₄₀₀ / T _700, as well as single transmittance, degree of polarization, the phase difference of iodine The value R _i and the b value of the orthogonal hue are adjusted within the predetermined or preferable numerical range.

For example, with respect to the above 3), if the draw ratio is too high, it becomes difficult to control the orthogonal transmittances T ₄₀₀ and T ₇₀₀ , so the final total draw ratio of the polyvinyl alcohol-based resin layer or film is 6.0 times or less. It is preferable that it is less than 5.7 times. On the other hand, if the draw ratio is too low, the absorption band itself on the long wavelength side is difficult to be formed, so the final total draw ratio of the polyvinyl alcohol-based resin layer or film may be more than 3 times. preferable. On the other hand, if the stretching temperature is too high, the crystallization of the polyvinyl alcohol resin proceeds excessively, making it difficult to control the orthogonal transmittances T ₄₀₀ and T ₇₀₀ . In order to make it easier to control the orthogonal transmittances T ₄₀₀ and T ₇₀₀ , the stretching is preferably performed both in the dyeing process and in the boric acid process.

  In addition, when the washing temperature in the washing treatment is too high, or when the immersion time in water is too long, the entire transmittance including the long wavelength side and the short wavelength side is increased, and accordingly, the polarizing performance of the polarizing plate Not only decreases, but also the b value of the orthogonal hue deviates from the range of -2.5 to -0.5. Therefore, the temperature of the water washing treatment is usually about 1-50 ° C, preferably about 3-40 ° C, more preferably about 5-30 ° C. Moreover, the immersion time in water is usually about 0.2 to 40 seconds, preferably about 0.5 to 30 seconds, and more preferably about 1 to 20 seconds.

  Referring to the guidelines regarding the influence factors as described above and the section of the examples described later, the optical characteristics of the above [a] to [d] are satisfied, and the b value of the orthogonal hue is preferably -2.5 to- Those skilled in the art can find various production conditions for obtaining a polarizing plate in the range of 0.5.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated further more concretely, this invention is not limited by these examples. In the following examples, the thicknesses of the polarizer and the protective film were measured using a digital micrometer “MH-15M” manufactured by Nikon Corporation.

(Production Example 1: Production of Polarizer 1)
After immersing an unstretched polyvinyl alcohol film (“VF-PE # 3000” manufactured by Kuraray Co., Ltd.) having an average polymerization degree of about 2400 and a saponification degree of 99.9 mol% and a thickness of 30 μm in pure water at 37 ° C., The dyeing treatment was performed by immersing in an aqueous solution having a weight ratio of iodine / potassium iodide / water of 0.04 / 1.5 / 100 at 30 ° C. Then, the boric acid treatment was performed by immersing in an aqueous solution having a weight ratio of potassium iodide / boric acid / water of 12 / 3.6 / 100 at 56.5 ° C. Subsequently, after washing with pure water at 10 ° C. for 4 seconds, drying treatment was performed at 85 ° C. to produce a polarizer 1 having a thickness of about 12 μm in which iodine was adsorbed and oriented on a uniaxially stretched polyvinyl alcohol film. Uniaxial stretching was mainly performed in the iodine staining and boric acid treatment steps. The draw ratio based on the unstretched polyvinyl alcohol film was 4.9 times, and the final neck-in ratio represented by the above formula was 41%.

(Production Example 2: Production of Polarizer 2)
Adsorption of iodine on the uniaxially stretched polyvinyl alcohol film is the same as in Production Example 1 except that the stretch ratio based on the unstretched polyvinyl alcohol film is 5.1 times and the final neck-in ratio is 42%. Thus, a polarizer 2 having a thickness of about 12 μm was produced.

(Production Example 3: Production of Polarizer 3)
Adsorption orientation of iodine on the uniaxially stretched polyvinyl alcohol film was the same as in Production Example 1 except that the stretch ratio based on the unstretched polyvinyl alcohol film was 4.7 times and the final neck-in rate was 39%. A polarizer 3 having a thickness of about 12 μm was produced.

(Production Example 4: Production of Polarizer 4)
Iodine is adsorbed and oriented on the uniaxially stretched polyvinyl alcohol film in the same manner as in Production Example 1 except that the stretch ratio based on the unstretched polyvinyl alcohol film is 4.5 times and the final neck-in ratio is 38%. A polarizer 4 having a thickness of about 12 μm was produced.

(Production Example 5: Production of polarizer 5)
After immersing an unstretched polyvinyl alcohol film (“VF-PE # 3000” manufactured by Kuraray Co., Ltd.) having an average polymerization degree of about 2400 and a saponification degree of 99.9 mol% and a thickness of 30 μm in pure water at 37 ° C., The dyeing treatment was performed by immersing in an aqueous solution having a weight ratio of iodine / potassium iodide / water of 0.04 / 1.5 / 100 at 30 ° C. Then, the boric acid treatment was performed by immersing in an aqueous solution having a weight ratio of potassium iodide / boric acid / water of 12 / 3.6 / 100 at 56.5 ° C. Subsequently, after washing with pure water at 10 ° C. for 2 seconds, a drying treatment was performed at 85 ° C. to prepare a polarizer 5 having a thickness of about 12 μm in which iodine was adsorbed and oriented on a uniaxially stretched polyvinyl alcohol film. Uniaxial stretching was mainly performed in the iodine staining and boric acid treatment steps. The draw ratio based on the unstretched polyvinyl alcohol film was 4.6 times, and the final neck-in rate was 40%.

(Production Example 6: Production of polarizer 6)
After immersing an unstretched polyvinyl alcohol film (“VF-PE # 3000” manufactured by Kuraray Co., Ltd.) having an average polymerization degree of about 2400 and a saponification degree of 99.9 mol% and a thickness of 30 μm in pure water at 20 ° C., Dyeing treatment was performed by immersing in an aqueous solution having a weight ratio of iodine / potassium iodide / water of 0.04 / 2/100 at 30 ° C. Then, it was immersed in an aqueous solution having a potassium iodide / boric acid / water weight ratio of 12 / 4.1 / 100 at 56 ° C., and then the potassium iodide / boric acid / water weight ratio was 9 / 2.9 / Boric acid treatment was performed by immersing in 100 aqueous solution at 40 ° C. Subsequently, after washing with pure water at 5 ° C. for 3 seconds, drying treatment was performed at 60 ° C. to produce a polarizer 6 having a thickness of about 12 μm in which iodine was adsorbed and oriented on a uniaxially stretched polyvinyl alcohol film. Uniaxial stretching was mainly performed in the iodine staining and boric acid treatment steps. The draw ratio based on the unstretched polyvinyl alcohol film was 5.8 times, and the final neck-in ratio represented by the above formula was 54%.

<Example 1>
(1) Preparation of adhesive 3 parts by weight of carboxyl group-modified polyvinyl alcohol [“KL-318” manufactured by Kuraray Co., Ltd.] was dissolved in 100 parts by weight of water to prepare an aqueous polyvinyl alcohol solution. To the obtained aqueous solution, 1.5 parts by weight of water-soluble polyamide epoxy resin (“Smile Resin 650 (30) manufactured by Taoka Chemical Industry Co., Ltd., solid content concentration: 30% by weight)” per 100 parts by weight of water. The aqueous adhesive was obtained by mixing at a ratio of

(2) Production of polarizing plate with double-sided protective film As protective film to be bonded to the polarizer, the following protective film:
First protective film: triacetyl cellulose (TAC) film with a hard coat layer [“25KCHCN-TC” manufactured by Toppan Printing Co., Ltd., thickness 32 μm],
Second protective film: cyclic polyolefin-based resin film [“ZF14” manufactured by Nippon Zeon Co., Ltd., thickness 23 μm]
Prepared.

  While bonding the 1st protective film which gave the saponification process to the bonding surface through the aqueous adhesive prepared above on the single side | surface of the polarizer 1 produced in manufacture example 1, it bonded on the other surface. The 2nd protective film which performed the saponification process on the surface was bonded through the same aqueous adhesive, and it crimped | bonded by passing between a pair of bonding rolls. Subsequently, it was dried in an oven at 80 ° C. for 5 minutes to obtain a polarizing plate with a double-sided protective film.

<Example 2, Comparative Examples 1-4>
Instead of the polarizer 1, the polarizer 2 produced in Production Example 2 (Example 2), the polarizer 3 produced in Production Example 3 (Comparative Example 1), and the polarizer 4 produced in Production Example 4 (Comparative Example 2) ), With a double-sided protective film in the same manner as in Example 1 except that the polarizer 5 produced in Production Example 5 (Comparative Example 3) and the polarizer 6 produced in Production Example 6 (Comparative Example 4) were used. A polarizing plate was produced.

[Measurement of optical properties of polarizing plate]
(1) Measurement of retardation value R _{i of} iodine and retardation value R _pva of polyvinyl alcohol (initial)
Immediately after manufacturing (initial _stage ) polarizing plate with a double-sided protective film (that is, for polarizing plates not _{subjected to} a heat resistance test), the values of R _i and R _pva (unit: nm) at a wavelength of 1000 nm were measured using a phase difference measuring device [Oji _Scientific Instruments Co., Ltd. ) “KOBRA-WPR / IR” manufactured by KK). Specifically, it is as follows.

R _i and R _pva are obtained by phase difference measurement in a wavelength region having no iodine absorption band. Specifically, the phase difference values at a plurality of wavelengths λ having a wavelength of 850 nm or more are measured using the phase difference measuring apparatus. The measured retardation value R (λ) at each wavelength λ is plotted, and this is expressed by the following Cellmeier equation:
R (λ) = A + B / (λ ² −600 ² )
Fitting with the least squares method. Here, A and B are fitting parameters, which are coefficients determined by the least square method.

At this time, the retardation value R (λ) can be separated into a retardation value R _pva of polyvinyl alcohol (PVA) having no wavelength dependence and a retardation value R _{i of} iodine having a strong wavelength dependence, R _pva and R _i are each represented by the following formula:
R _pva = A
R _i = B / (λ ² −600 ² )
It is represented by Based on these formulas, values of R _i and R _{pva and} a value of R _i / R _{pva at} a wavelength λ = 1000 nm were calculated. The results are shown in Table 1.

(2) Measurement of orthogonal transmittances T ₄₀₀ and T ₇₀₀ , b value of orthogonal hue, visibility corrected single transmittance Ty, and visibility corrected polarization degree Py (initial)
About the polarizing plate with a double-sided protective film (that is, a polarizing plate that has not been subjected to a heat resistance test) immediately after production (initial stage), an acrylic pressure-sensitive adhesive sheet (with a release film) is bonded to the outer surface of the second protective film. An attached polarizing plate was produced. A test piece having a size of about 30 mm in length and about 30 mm in width was cut out from the polarizing plate with the pressure-sensitive adhesive layer, the release film was peeled off from the pressure-sensitive adhesive layer, and then bonded to a glass plate through the exposed pressure-sensitive adhesive layer. A measurement sample was prepared. About the obtained measurement sample, the various optical characteristics of the title were measured. The results are shown in Table 1. At the time of measurement, the measurement sample was set so that incident light was incident on the glass surface side. The various optical properties of the title are based on the following definitions and measurement methods.

The orthogonal transmittance T is a value obtained by correcting the visibility with a 2-degree field of view (C light source) of JlS Z 8701, and a spectrophotometer with an integrating sphere [“V7100” manufactured by JASCO Corporation, a 2-degree field of view; C light source]. Using this spectrophotometer, MD transmittance and TD transmittance were determined in the wavelength range of 380 to 780 nm. TD transmittance at a wavelength of 400nm is T _400, TD transmittance at a wavelength of 700nm is T _700. “TD transmittance” is the transmittance when the direction of polarized light emitted from the Glan-Thompson prism is orthogonal to the transmission axis of the measurement sample.

  The orthogonal hue means a hue of light transmitted from the other surface when light is applied from one surface in a state where two polarizing plates are overlapped so that their absorption axes are orthogonal to each other. The hues here are a and b expressed in the Lab color system, and were measured using a spectrophotometer with an integrating sphere equipped with a C light source (“V7100” manufactured by JASCO Corporation).

Polarization characteristics of a polarizing plate can be expressed by a single transmittance and a degree of polarization, each of the following formula:
Single transmittance (λ) = 0.5 × (Tp (λ) + Tc (λ))
Polarization degree (λ) = 100 × (Tp (λ) −Tc (λ)) / (Tp (λ) + Tc (λ))
Defined by

  Tp (λ) is the transmittance (%) of the polarizing plate measured in relation to the linearly polarized light with the incident wavelength λnm and parallel Nicol, and Tc (λ) is the relationship between the incident linearly polarized light with the wavelength λnm and crossed Nicols. It is the transmittance | permeability (%) of the polarizing plate measured by. However, the visibility corrected single transmittance (Ty) and the visibility corrected polarization degree (Py) obtained by performing the visibility correction on the single transmittance (λ) and the polarization degree (λ) obtained for each wavelength, respectively. ), And the single transmittance and the degree of polarization in this specification indicate the visibility corrected single transmittance (Ty) and the visibility corrected polarization degree (Py), respectively. Ty and Py were also measured using a spectrophotometer with an integrating sphere equipped with a C light source [“V7100” manufactured by JASCO Corporation].

[Evaluation of heat resistance of polarizing plate]
(1) Measurement of the change rate Z of the visibility correction polarization degree before and after the heat test The heat measurement test in which the measurement sample having various initial optical characteristics was put into an oven set at 85 ° C. (dry) for 500 hours was conducted. Then, it was taken out from the oven, and the visibility correction polarization degree Py ′ after the heat resistance test was measured in the same manner as described above. Based on the measurement results, the following formula:
Rate of change Z (%) in visibility correction polarization degree = 100 × (initial visibility correction polarization degree Py−visibility correction polarization degree Py ′ after heat test) / (initial visibility correction polarization degree Py)
The change rate Z of the visibility correction polarization degree before and after the heat resistance test was calculated. The results are shown in Table 1.

(2) Evaluation of red discoloration by heat test For the polarizing plate with a double-sided protective film (that is, the polarizing plate not subjected to the heat test) immediately after production (initial stage), an acrylic pressure-sensitive adhesive sheet (release film) is formed on the outer surface of the second protective film. Attached) was prepared to produce a polarizing plate with an adhesive layer. Two 5.1-inch (about 64 mm long × about 113 mm wide) test pieces were cut out from this polarizing plate with an adhesive layer. After peeling and removing the release film from the pressure-sensitive adhesive layers of the two test pieces, these test pieces were bonded to a glass plate through the exposed pressure-sensitive adhesive layer to prepare a measurement sample. At this time, the test pieces arranged on both sides were in a crossed Nicol positional relationship. The measurement sample was subjected to the same heat resistance test as described above, then taken out of the oven, and visually evaluated for redness on a backlight in a dark room. The indicators of redness level are as shown below. Up to Lv3 was accepted. The results are shown in Table 1.

Lv1: Level without any redness,
Lv2: Level that keeps a black state and cannot visually recognize redness,
Lv3: It looks like the color is slightly lighter than the one before the heat test, but there is almost no redness.
Lv4: The level that has changed to reddish overall,
Lv5: Level completely changed to red.

  1, 2 Polarizer, 5 Polarizer, 10 First protective film, 15 First adhesive layer, 20 Second protective film, 25 Second adhesive layer.

Claims (4)

A polyvinyl alcohol resin layer containing a polarizer having a thickness of 15 μm or less in which iodine is adsorbed and oriented,
Retardation value R _i of the iodine at a wavelength of 1000nm is at 160nm than 220nm or less,
The single transmittance Ty is 41 to 43%, the degree of polarization Py is 99.9% or more, and the ratio T ₄₀₀ / T between the orthogonal transmittance T ₄₀₀ at a wavelength of ₄₀₀ nm and the orthogonal transmittance T ₇₀₀ at a wavelength of 700 nm. ₇₀₀ is 1 or more,
The iodine phase difference value R _i is measured by plotting phase difference values R (λ) at a plurality of wavelengths λ having a wavelength of 850 nm or more, and this is plotted as the following Cellmeier equation [1]:
R (λ) = A + B / (λ ² −600 ² ) [1]
When fitting with the least squares method, the following equation [2]:
R _i = B / (λ ² −600 ² ) [2]
(In Formula [2], B is a fitting parameter when fitting by the least square method, and λ is 1000 nm.)
A polarizing plate required as   The polarizing plate according to claim 1, wherein the b value of the orthogonal hue is −2.5 to −0.5.   The polarizing plate of Claim 1 or 2 whose change rate of the said polarization degree before and behind the heat test which heats at 85 degreeC for 500 hours is 0.05% or less.   The polarizing plate according to claim 1, further comprising a protective film laminated on at least one surface of the polarizer.

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