JP2010026498A - Polarizing plate and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarizing plate capable of satisfying high durability, and a method for manufacturing the same. <P>SOLUTION: The polarizing plate includes protective films on both sides of a polarizer formed by dyeing a polyvinyl alcohol film with iodine. In the polarizing plate, the ratio T<SB>2</SB>/T<SB>1</SB>of the maximum peak intensity T<SB>1</SB>in a range of 105±5 cm<SP>-1</SP>by a Raman spectroscopy in a central part in the thickness direction of the polarizer section and the maximum peak intensity T<SB>2</SB>in a range of 105±5 cm<SP>-1</SP>by a Raman spectroscopy at the end part in the thickness direction of the polarizer is 0.920 to 0.985. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a polarizing plate and a method for producing the same. The present invention also relates to an optical film using the polarizing plate and an image display device such as a liquid crystal display device, an organic EL display device, and a PDP.

  Conventionally, as a polarizing plate used for an image display device such as a liquid crystal display device, since it has high transmittance and polarization degree, a polarizer made of a polyvinyl alcohol film dyed with iodine, a triacetyl cellulose film, etc. A laminate of protective films is used.

  In recent years, with the wide use of liquid crystal display devices, they are often used for a long time under high temperature conditions and the like, and there is a demand for liquid crystal display devices with little change in image quality according to the application used. Yes. Accordingly, the polarizing plate is also required to have durability that does not deteriorate the optical characteristics when left under high temperature conditions or when left under high temperature and high humidity conditions.

  For example, it is shown that durability under high-temperature and high-humidity conditions is improved by using a polyvinyl alcohol film with a high degree of polymerization, controlling the method of stretching the polarizer, or further drying after laminating the protective film. (For example, refer to Patent Document 1). Moreover, it is shown that durability is improved by carrying out high temperature and humidification processing after laminating | stacking a protective film (for example, refer patent document 2).

  However, the polarizing plate described in the above-mentioned patent document may not have sufficient durability or may lack hue neutrality. Due to the expansion of the field of application of image display devices, higher durability is desired for the polarizing plate.

JP-A-9-197127 JP 2006-23573 A

  An object of this invention is to provide the polarizing plate which consists of a polyvinyl alcohol-type film, and was excellent in durability, and its manufacturing method.

  Another object of the present invention is to provide an optical film using the polarizing plate, and further an image display device using the polarizing plate and the optical film.

As a result of intensive studies, the inventors of the present application have found that the above problems can be solved by a polarizing plate including a polarizer having a Raman spectral peak intensity distribution in the thickness direction, and have reached the present invention.
That is, the present invention is a polarizing plate provided with protective films on both sides of a polarizer obtained by dyeing a polyvinyl alcohol film with iodine, and a range of 105 ± 5 cm ⁻¹ by Raman spectroscopy at the center in the thickness direction of the polarizer cross section. between the maximum peak intensity T _1, the ratio of the maximum peak intensity T ₂ of the range of 105 ± 5 cm ^-1 by Raman spectroscopy in the thickness direction end portion of the polarizer is a polarizing plate which satisfy the following relationship.
0.920 ≦ T ₂ / T ₁ ≦ 0.985

Furthermore, this invention relates to the manufacturing method of the said polarizing plate.
In the method for producing a polarizing plate of the present invention, the polyvinyl alcohol film is subjected to at least an iodine staining step and a crosslinking step in this order to obtain a polarizer, and a step of laminating a protective film on the obtained polarizer. It is preferable that the ratio (t _C / t _B ) of the dye bath immersion time (t _B ) in the iodine dyeing step and the cross-linking bath immersion time (t _C ) in the crosslinking step is 1.30 to 3.90. .

  Furthermore, in the manufacturing method of the polarizing plate of this invention, it is preferable to give the process (hue adjustment process) immersed in the solution whose potassium iodide density | concentration is 1 to 5 weight% after a bridge | crosslinking process.

  The present invention also relates to an optical film in which at least one polarizing plate is used, and an image display device in which the polarizing plate or the optical film is used.

Peak around 105 cm ^-1 in Raman spectroscopy, polyvinyl alcohol and _{I 3} ^- ions complex _{(PVA-I 3} ^- complex) correspond to the Raman scattering. In the present invention, the peak intensity in the Raman spectroscopy and the thickness direction central portion and the end portion is a specific ratio, namely, in the thickness direction, PVA-I ₃ ^- complex comprises a polarizer having a predetermined concentration distribution This increases the durability of the polarizing plate.

The polarizing plate of the present invention is obtained by laminating protective films on both surfaces of a polarizer obtained by subjecting a polyvinyl alcohol film to an iodine staining treatment. The polarizing plate of the present invention has a maximum peak intensity T ₁ near 105 cm ⁻¹ by Raman spectroscopy at the central portion in the thickness direction of the polarizer cross-section, and a Raman spectrum at the end in the thickness direction of the polarizer. The ratio with the maximum peak intensity T ₂ near 105 cm ⁻¹ by the method satisfies the relationship of 0.920 ≦ T ₂ / T ₁ ≦ 0.985. The peak intensity ratio T ₂ / T ₁ is preferably 0.930 or more, more preferably 0.950 or more, and further preferably 0.955 or more. When the peak intensity ratio is out of the above range, the durability of the polarizing plate tends to decrease. The Raman spectrum can be measured by Ar ⁺ laser irradiation with an excitation wavelength of 514.5 nm. Note that the maximum peak intensity in the vicinity of 105 cm ^-1, is that the Raman scattering intensity of a peak top in the range of 105 ± ^{5 cm -1.}

In general, iodine is present as a complex of triiodine ion (I ₃ ⁻ ) and pentaiodine ion (I ₅ ⁻ ) and polyvinyl alcohol (PVA) in a polarizer subjected to iodine staining. peak around 105 cm ^-1 is, PVA and _{I 3} ^- corresponding to the Raman scattering ^- complexes (complexes _{PVA-I 3)} with. Therefore, this peak is that meet specific ratios, PVA-I ₃ in the polarizer ^- means that complex has a predetermined concentration distribution in the thickness direction.

The polarizing plate of the present invention has a protective film on both sides of a polarizer obtained by dyeing a polyvinyl alcohol film with iodine, and if the peak intensity ratio T ₂ / T _{1 of} Raman spectroscopy is in the above range, other configurations and Although a manufacturing method is not specifically limited, Details are given below about the preferable aspect of the manufacturing method of the polarizer which comprises the polarizing plate of this invention, a protective film, and a polarizing plate.

[Polarizer]
As the polarizer constituting the polarizing plate of the present invention, a polyvinyl alcohol-based polarizer containing iodine is used. Polyvinyl alcohol or a derivative thereof is used as a material for the polyvinyl alcohol film applied to the polarizer. Derivatives of polyvinyl alcohol include polyvinyl formal, polyvinyl acetal and the like, olefins such as ethylene and propylene, unsaturated carboxylic acids such as acrylic acid, methacrylic acid and crotonic acid, alkyl esters thereof, acrylamide and the like. can give. The degree of polymerization of polyvinyl alcohol is preferably about 100 to 10000, more preferably 1000 to 10000, still more preferably 1000 to 8000, and particularly preferably 2000 to 6000. A saponification degree of about 80 to 100 mol% is preferably used.

  Moreover, although a polarizer is generally obtained by iodine dyeing | staining and extending | stretching, in the polarizer which comprises the polarizing plate of this invention, it is preferable that the film thickness of the original film before extending | stretching is 20-100 micrometers, 40 More preferably, it is -75 micrometers.

  The polyvinyl alcohol film may contain an additive such as a plasticizer. Examples of the plasticizer include polyols and condensates thereof, and examples thereof include glycerin, diglycerin, triglycerin, ethylene glycol, propylene glycol, and polyethylene glycol. The amount of the plasticizer used is not particularly limited, but is preferably 20% by weight or less in the polyvinyl alcohol film.

[Production method of polarizer]
The method for producing such a polarizer is not particularly limited, but at least the step of immersing the polyvinyl alcohol film in a solution (dye bath) containing iodine and / or iodine ions (hereinafter referred to as “iodine dyeing step”). And a step of immersing in a solution (crosslinking bath) containing a crosslinking agent such as boric acid (hereinafter sometimes referred to as “crosslinking step”) after the iodine staining step, and dyeing in the iodine staining step The ratio t _C / t _{B of the} bath immersion time t _B and the crosslinking bath immersion time t _C in the crosslinking step is preferably 1.30 to 3.90, more preferably 1.40 to 3.00. More preferably, it is 1.50 to 2.60.

When the ratio t _C / t _B of the immersion time of the “iodine dyeing step” and the “crosslinking step” is within the above range, the maximum peak intensity T ₁ near 105 cm ⁻¹ by Raman spectroscopy at the center in the thickness direction, The ratio of the maximum peak intensity T ₂ near 105 cm ⁻¹ by Raman spectroscopy at the end in the thickness direction of the polarizer is within the above-described preferable range, and the color loss of iodine tends to be suppressed under high temperature and high humidity. .

On the other hand, when t _C / t _B is small, the iodine ion concentration at the central portion in the thickness direction of the polarizer is relatively higher than the iodine ion concentration near the surface of the polarizer, that is, T ₂ / T ₁ is Below the preferred range, the durability tends to decrease. The reason why the durability varies depending on the ratio of the immersion time is not necessarily clear. However, since the immersion time t _C in the “crosslinking step” is relatively short, the crosslinking of PVA with boric acid may be insufficient. It is considered as a cause. When PVA crosslinking is insufficient, in a high temperature and high humidity environment, an iodine ion (PVA-I ₃ ^- complex) estimation for becomes unstable, large degradation of the optical properties, and that lacks neutrality hue Is done. In addition, since the immersion time t _B in the “iodine dyeing step” is relatively long, it is estimated that the presence of iodine uniformly in the thickness direction of the polarizer also affects the durability.

On the contrary, when t _C / t _B is large, the iodine ion concentration in the central portion in the thickness direction of the polarizer is relatively low. Therefore, T ₂ / T ₁ exceeds the above preferable range, and the durability tends to decrease. is there. Thus, one reason that the immersion time affects the durability is that the immersion time t _C in the “crosslinking step” is relatively long, so that the crosslinking of PVA with boric acid proceeds excessively. Thus crosslinking proceeds excessively, _{PVA-I 3} ^- It is believed that the complex is more produced, _{PVA-I 3} ^- complex _{PVA-I 5} ^- than the complex, in a high-temperature and high-humidity environment Since relative stability is lacking, it is presumed that optical properties are greatly deteriorated and hue neutrality is lacking. In addition, since the immersion time t _B in the “iodine dyeing step” is relatively short, the end portion (surface) in the thickness direction of the polarizer is selectively dyed with iodine as compared with the central portion, thereby causing boric acid. It is presumed that the deterioration of optical properties in a high temperature and high humidity environment is increased due to the inhibition of crosslinking and insufficient crosslinking.

(Iodine staining process)
The iodine dyeing step can be performed by adsorbing and orienting iodine and / or iodine ions on the polyvinyl alcohol film. Dyeing is performed by immersing the polyvinyl alcohol film in a dyeing bath having an iodine solution. As the iodine aqueous solution used as the iodine solution, an aqueous solution containing iodine ions by a dissolution aid such as iodine and potassium iodide is used. The iodine concentration is preferably about 0.01 to 0.5% by weight, and more preferably 0.02 to 0.4% by weight. The potassium iodide concentration is preferably about 0.01 to 10% by weight, more preferably 0.02 to 8% by weight.

In the iodine dyeing treatment, the temperature of the iodine solution in the dyeing bath is usually about 20 to 50 ° C, and preferably 25 to 40 ° C. The immersion time t _B in the dyeing bath is usually preferably about 10 to 300 seconds, more preferably in the range of 20 to 240 seconds, further preferably 20 to 200 seconds, and 25 to 120 seconds. It is particularly preferred.

  In the iodine dyeing step, it is preferable to perform uniaxial stretching in the dyeing solution. The stretching ratio in the case of stretching is usually 3.5 times or less based on the length of the polyvinyl alcohol film (hereinafter sometimes referred to as “original length”) in an unstretched state. It is preferably 3 times or less, and more preferably 3 times or less. In addition, from the standpoint of preventing uneven dyeing and preventing wrinkles, it is preferably stretched at a draw ratio of 2 times or more, more preferably 2.5 times or more based on the original length before being subjected to the iodine dyeing step.

(Swelling process)
Before being subjected to the iodine dyeing step, the polyvinyl alcohol film can be swelled by immersing it in water or the like, if necessary. By such a swelling process, the polyvinyl alcohol-based film is washed with water, so that dirt on the film surface and an anti-blocking agent can be washed. In addition, by swelling the polyvinyl alcohol film, there is an effect of preventing unevenness such as uneven coloring.

  As the swelling bath for swelling the polyvinyl alcohol film, water is mainly used, but it is preferable that a plasticizer is further contained. When the swelling bath has a plasticizer, the amount of plasticizer eluted from the polyvinyl alcohol film can be controlled and the film swelling amount can be made uniform in the swelling step. When the swelling bath contains a plasticizer, the content thereof is not particularly limited, but it is preferably 0.5 to 15% by mass and preferably 0.5 to 5.0% by mass with respect to the total amount of the aqueous solution. Is more preferable. If the plasticizer content is too low, the swelling action of the film may be insufficient, and if it is too high, it may be difficult to perform stretching to satisfy the optical properties as a polarizing plate. is there.

  Here, the plasticizer is not particularly limited as long as it can plasticize a polyvinyl alcohol film, and a conventionally known plasticizer can be used. Examples thereof include glycols such as ethylene glycol, diethylene glycol, propylene glycol, and low molecular weight polyethylene glycol (Mw: 200 to 400), glycerin derivatives such as glycerin, diglycerin, and triglycerin. Among these, a glycerin derivative is preferable from the viewpoint of strong interaction with polyvinyl alcohol and high compatibility, and glycerin is particularly preferable.

  In the swelling step, the immersion time of the polyvinyl alcohol film in the swelling bath is preferably 20 seconds or longer and 70 seconds or shorter, and more preferably 30 seconds or longer and 60 seconds or shorter. If the immersion time is less than 20 seconds, the swelling effect may be insufficient, and if the immersion time exceeds 70 seconds, the swelling may be excessively advanced, resulting in a problem in productivity. The temperature of the aqueous solution in the swelling bath is usually set in the range of 20 to 60 ° C.

  In addition, the swelling step may employ a method of applying a swelling treatment while applying or spraying water or a plasticizer-containing aqueous solution onto a polyvinyl alcohol film in addition to being immersed in a swelling bath as described above. .

  Furthermore, in the swelling step, stretching can be performed as described above. When extending | stretching by a swelling process, it is preferable that the draw ratio is 2 times or more on the basis of original length as mentioned above, Furthermore, it is preferable that it is 2.5 times or more.

(Crosslinking process)
The dyed polyvinyl alcohol film is preferably crosslinked. As the crosslinking solution for carrying out the crosslinking treatment, it is usually preferable to use an aqueous solution having a concentration of 1 to 15% by weight of a crosslinking agent in which a crosslinking agent such as boric acid, borax, glyoxal, or glutaraldehyde is used alone or mixed. It is more preferable to use a 10% by weight aqueous solution, it is more preferable to use a 2-7% by weight aqueous solution, and it is particularly preferable to use a 3-6% by weight aqueous solution. The concentration of the cross-linking agent can be determined in consideration of the balance of the polarizing plate shrinkage caused by the optical characteristics and the stretching force generated in the polyvinyl alcohol film.

In the crosslinking bath, potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, titanium iodide, etc. It is preferable to add an auxiliary such as iodide to a concentration of 0.05 to 15% by weight, more preferably 0.5 to 8% by weight, and 2 to 5% by weight. More preferably, it is added. By having these additives, the characteristics of the polarizer can be made uniform in the plane. The temperature of the aqueous solution is usually about 20 to 70 ° C, preferably 25 to 65 ° C, and more preferably 30 to 60 ° C. The immersion time is not particularly limited, but is usually about 15 seconds to 900 seconds, preferably 30 seconds to 600 seconds, more preferably 30 to 250 seconds, and further preferably 50 to 150 seconds. preferable. Further, from the viewpoint of improving the durability of the polarizing plate, the ratio t _C / t _B of the dye bath immersion time t _B and the cross-linking bath immersion time t _C in the cross-linking step is set to a predetermined range as described above. preferable. The crosslinking bath may contain a small amount of an organic solvent compatible with water in addition to water.

  The draw ratio of the polyvinyl alcohol film in the crosslinking step is preferably about 4 to 8 times the original length, and more preferably about 5 to 7 times. When the draw ratio is excessively high, the film tends to break. On the other hand, if the draw ratio is too low, the polarization degree of the polarizing plate may be insufficient.

  In the crosslinking step, a plurality of crosslinking baths having different types and concentrations of solutes in the solution can be used. When a plurality of crosslinking baths are used, it is preferable that the concentration of the crosslinking agent such as boric acid and the concentration of auxiliary agents such as potassium iodide are higher in the subsequent crosslinking bath than in the previous crosslinking bath. By increasing the concentration of the later crosslinking bath, a polarizing plate having excellent uniformity and durability can be obtained. The stretching in the cross-linking step may be performed in one or both of the previous cross-linking bath and the subsequent cross-linking bath, and both may be stretched at different magnifications. In particular, as described above, it is preferable that the draw ratio in the cross-linking bath after relatively increasing the concentration of the cross-linking agent and auxiliary agent is larger than the draw ratio in the previous cross-linking bath. Thus, by adjusting the draw ratio, a polarizing plate having a high degree of polarization can be obtained.

  Stretching can also be performed in multiple stages in one bath. In multistage stretching, for example, a plurality of pinch roll (nip roll) pairs are provided in a bath, and stretching is performed between each pair of rolls. When stretching is performed in multiple stages, the stretching ratio for each stage can be made different by controlling the peripheral speed of each pair of pinch rolls.

(Hue adjustment process)
Moreover, it is preferable to use for the hue adjustment process which the polyvinyl-alcohol-type film which performed iodine adsorption orientation processing is further immersed in iodide aqueous solutions (iodine impregnation bath), such as potassium iodide. The iodide used for the impregnation bath is preferably potassium iodide. Further, from the viewpoint of sufficiently impregnating, the potassium iodide concentration is preferably 1 to 5% by weight, and more preferably 2 to 4% by weight. The liquid temperature in an iodine impregnation bath is 10-60 degreeC normally, Preferably it is about 15-40 degreeC, More preferably, it is 20-30 degreeC. Moreover, the immersion time of the impregnation bath is preferably 1 second to 60 seconds, more preferably 1 to 30 seconds, further preferably 3 to 30 seconds, and 3 to 15 seconds. Particularly preferred. Setting the immersion time of the impregnation bath and the iodide concentration in the above ranges is preferable from the viewpoint of hue adjustment when polarizing plates are arranged orthogonally.

  In addition to the above steps, metal ion treatment can be performed. The metal ion treatment is performed by immersing a polyvinyl alcohol film in an aqueous solution containing a metal salt. Various metal ions can be contained in the polyvinyl alcohol film by the metal ion treatment.

  As metal ions, metal ions of transition metals such as cobalt, nickel, zinc, chromium, aluminum, copper, manganese, and iron are particularly preferably used in terms of color tone adjustment and durability. Among these metal ions, zinc ions are preferable from the viewpoints of color tone adjustment and heat resistance. Examples of the zinc salt include zinc halides such as zinc chloride and zinc iodide, zinc sulfate, and zinc acetate.

  A metal salt solution is used for the metal ion treatment. Hereinafter, zinc impregnation treatment will be described as a representative example of the case of using a zinc salt aqueous solution among metal ion treatments.

  The concentration of zinc ions in the aqueous zinc salt solution is preferably about 0.1 to 10% by weight, more preferably 0.3 to 7% by weight. The zinc salt solution is preferably an aqueous solution containing potassium ions and iodine ions with potassium iodide or the like because it is easy to impregnate zinc ions. The potassium iodide concentration in the zinc salt solution is preferably about 0.1 to 10% by weight, more preferably 0.2 to 5% by weight. From this viewpoint, it is preferable to perform metal ion treatment in the cross-linking step or the hue adjusting step.

(Drying process)
It is preferable that the polarizer thus obtained is finally subjected to a drying step. In the drying step, the drying time and the drying temperature are appropriately set according to the moisture content required for the obtained polarizer. The drying temperature is usually in the range of 20 to 150 ° C, but preferably in the range of 40 to 100 ° C. If the drying temperature is too low, the drying time becomes longer and the production efficiency may decrease. If the drying temperature is too high, the obtained polarizer may be deteriorated, resulting in insufficient optical properties and hue. The heat drying time is usually about 1 to 5 minutes.

  The thickness of the polarizer is not particularly limited, but is generally about 5 to 80 μm. When the thickness of the polarizer is reduced, moisture in the polarizer is likely to be volatilized in a drying process or the like when being bonded to the protective film.

[Formation of polarizing plate]
(Transparent protective film)
The obtained polarizer can be made into a polarizing plate by laminating a transparent protective film on both surfaces according to a conventional method. As a material constituting the transparent protective film, for example, a thermoplastic resin excellent in transparency, mechanical strength, thermal stability, moisture barrier property, isotropy and the like is used. Specific examples of such thermoplastic resins include cellulose resins such as triacetyl cellulose, polyester resins, polyethersulfone resins, polysulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, (meth) acrylic resins, cyclic Examples thereof include polyolefin resins (norbornene resins), polyarylate resins, polystyrene resins, polyvinyl alcohol resins, and mixtures thereof. In addition, a transparent protective film is usually bonded to the polarizer by an adhesive layer. As the transparent protective film, thermosetting such as (meth) acrylic, urethane-based, acrylurethane-based, epoxy-based, silicone-based, etc. Resin or ultraviolet curable resin can be used.

  Although the thickness of a transparent protective film can be determined suitably, generally it is about 1-500 micrometers from points, such as workability | operativity, such as intensity | strength and handleability, and thin layer property. 1-300 micrometers is especially preferable, and 5-200 micrometers is more preferable. The transparent protective film is particularly suitable when the thickness is 5 to 150 μm.

  In addition, when providing a transparent protective film on both sides of a polarizer, the protective film which consists of the same polymer material may be used by the front and back, and the protective film which consists of a different polymer material etc. may be used.

  As the transparent protective film of the present invention, it is preferable to use at least one selected from cellulose resin, polycarbonate resin, cyclic polyolefin resin, and (meth) acrylic resin. Further, the transparent protective film may also be used as a retardation plate described later.

  Examples of the retardation plate include a birefringent film obtained by uniaxially or biaxially stretching a polymer material, a liquid crystal polymer alignment film, and a liquid crystal polymer alignment layer supported by a film. The thickness of the retardation plate is not particularly limited, but is generally about 20 to 150 μm.

  Examples of the polymer material include polyvinyl alcohol, polyvinyl butyral, polymethyl vinyl ether, polyhydroxyethyl acrylate, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, polycarbonate, polyarylate, polysulfone, polyethylene terephthalate, polyethylene naphthalate, polyether sulfone, Polyphenylene sulfide, polyphenylene oxide, polyallylsulfone, polyamide, polyimide, polyolefin, polyvinyl chloride, cellulose resin, cyclic polyolefin resin (norbornene resin), or any of these binary, ternary copolymers, graft copolymers Examples thereof include polymers and blends. These polymer materials become an oriented product (stretched film) by stretching or the like.

  Examples of the liquid crystal polymer include various main chain types and side chain types in which a conjugated linear atomic group (mesogen) imparting liquid crystal alignment is introduced into the main chain or side chain of the polymer. . Specific examples of the main chain type liquid crystal polymer include a nematic alignment polyester liquid crystal polymer, a discotic polymer, and a cholesteric polymer having a structure in which a mesogenic group is bonded at a spacer portion that imparts flexibility. Specific examples of the side chain type liquid crystal polymer include polysiloxane, polyacrylate, polymethacrylate, or polymalonate as a main chain skeleton, and a nematic alignment-providing para-substitution through a spacer portion composed of a conjugated atomic group as a side chain. Examples thereof include those having a mesogenic part composed of a cyclic compound unit. These liquid crystal polymers can be prepared by, for example, applying a solution of a liquid crystalline polymer on an alignment surface such as a surface of a thin film such as polyimide or polyvinyl alcohol formed on a glass plate, or an oblique deposition of silicon oxide. This is done by developing and heat treatment.

  The retardation plate may have an appropriate retardation according to the purpose of use, such as those for the purpose of compensating for various wavelength plates or birefringence of liquid crystal layers and compensation of viewing angle, etc. It may be one in which retardation plates are stacked and optical characteristics such as retardation are controlled.

  The retardation plate has a relationship of nx = ny> nz, nx> ny> nz, nx> ny = nz, nx> nz> ny, nz = nx> ny, nz> nx> ny, nz> nx = ny. What is satisfactory is selected and used according to various applications. Note that ny = nz includes not only the case where ny and nz are completely the same, but also the case where ny and nz are substantially the same.

  The transparent protective film may be subjected to surface modification treatment before applying the adhesive. Specific examples of the treatment include corona treatment, plasma treatment, primer treatment, and saponification treatment.

(surface treatment)
The surface of the transparent protective film to which the polarizer is not adhered may be subjected to a hard coat layer, antireflection treatment, antisticking, or surface treatment for the purpose of diffusion or antiglare.

(Lamination of polarizer and transparent protective film)
An adhesive is used for the adhesion treatment between the polarizer and the transparent protective film. Examples of the adhesive include isocyanate adhesives, polyvinyl alcohol adhesives, gelatin adhesives, vinyl latexes, and water-based polyesters. The said adhesive agent is normally used as an adhesive agent which consists of aqueous solution, and contains 0.5 to 60 weight% of solid content normally. In addition to the above, examples of the adhesive between the polarizer and the transparent protective film include an ultraviolet curable adhesive and an electron beam curable adhesive. The electron beam curable polarizing plate adhesive exhibits suitable adhesion to the various transparent protective films. In particular, it exhibits good adhesion even with respect to acrylic resins for which it was difficult to satisfy the adhesion.

  The polarizing plate of the present invention is produced by bonding the transparent protective film and the polarizer using the adhesive. The adhesive may be applied to either the transparent protective film or the polarizer, or to both. After the bonding, a drying process is performed to form an adhesive layer composed of a coating dry layer. Bonding of a polarizer and a transparent protective film can be performed with a roll laminator or the like. The thickness of the adhesive layer is not particularly limited, but is usually about 30 to 1000 nm.

[Optical film]
The polarizing plate of the present invention can be used as an optical film laminated with another optical layer in practical use. The optical layer is not particularly limited. For example, for forming a liquid crystal display device such as a reflection plate, a semi-transmission plate, a retardation plate (including wavelength plates such as 1/2 and 1/4), and a viewing angle compensation film. One or more optical layers that may be used can be used. In particular, a reflective polarizing plate or a semi-transmissive polarizing plate in which a polarizing plate or a semi-transmissive reflecting plate is further laminated on the polarizing plate of the present invention, an elliptical polarizing plate or a circularly polarizing plate in which a retardation plate is further laminated on the polarizing plate. A wide viewing angle polarizing plate obtained by further laminating a viewing angle compensation film on a plate or a polarizing plate, or a polarizing plate obtained by further laminating a brightness enhancement film on the polarizing plate is preferable.

(Reflective polarizing plate)
A reflective polarizing plate is a polarizing plate provided with a reflective layer, and is used to form a liquid crystal display device or the like that reflects incident light from the viewing side (display side). Such a light source can be omitted, and the liquid crystal display device can be easily thinned. The reflective polarizing plate can be formed by an appropriate method such as a method in which a reflective layer made of metal or the like is attached to one side of the polarizing plate via a transparent protective film or the like, if necessary.

(Transflective polarizing plate)
The semi-transmissive polarizing plate can be obtained by using a semi-transmissive reflective layer such as a half mirror that reflects and transmits light with the reflective layer. A transflective polarizing plate is usually provided on the back side of a liquid crystal cell, and displays an image by reflecting incident light from the viewing side (display side) when a liquid crystal display device is used in a relatively bright atmosphere. In a relatively dark atmosphere, a liquid crystal display device or the like that displays an image using a built-in light source such as a backlight built in the back side of the transflective polarizing plate can be formed.

(Oval and circular polarizers)
An elliptically polarizing plate or a circularly polarizing plate in which a retardation plate is further laminated on a polarizing plate will be described. A phase difference plate or the like is used when changing linearly polarized light to elliptically polarized light or circularly polarized light, changing elliptically polarized light or circularly polarized light to linearly polarized light, or changing the polarization direction of linearly polarized light. In particular, a so-called quarter-wave plate (also referred to as a λ / 4 plate) is used as a retardation plate that changes linearly polarized light into circularly polarized light or changes circularly polarized light into linearly polarized light. A half-wave plate (also referred to as a λ / 2 plate) is usually used when changing the polarization direction of linearly polarized light.

  The elliptically polarizing plate is effectively used for black and white display without the above color by compensating (preventing) the coloration (blue or yellow) generated by the birefringence of the liquid crystal layer of the super twist nematic (STN) type liquid crystal display device. It is done. Further, the one in which the three-dimensional refractive index is controlled is preferable because it can compensate (prevent) coloring that occurs when the screen of the liquid crystal display device is viewed from an oblique direction. The circularly polarizing plate is effectively used, for example, when adjusting the color tone of an image of a reflective liquid crystal display device in which an image is displayed in color, and also has an antireflection function. Specific examples of the retardation plate include a birefringent film obtained by stretching a film made of an appropriate polymer such as polycarbonate, polyvinyl alcohol, polystyrene, polymethyl methacrylate, polypropylene, other polyolefins, polyarylate, and polyamide. And an alignment film of a liquid crystal polymer, and an alignment layer of a liquid crystal polymer supported by a film. The retardation plate may have an appropriate retardation according to the purpose of use, such as those for the purpose of compensating for various wavelength plates or birefringence of liquid crystal layers, compensation of viewing angle, and the like. What laminated | stacked a phase difference plate and controlled optical characteristics, such as phase difference, etc. may be used.

  The elliptical polarizing plate and the reflective elliptical polarizing plate are obtained by laminating a polarizing plate or a reflective polarizing plate and a retardation plate in an appropriate combination. Such an elliptically polarizing plate or the like can also be formed by sequentially laminating them sequentially in the manufacturing process of the liquid crystal display device so as to be a combination of a (reflection type) polarizing plate and a retardation plate. An optical film such as a polarizing plate has an advantage that it can improve the production efficiency of a liquid crystal display device and the like because of excellent quality stability and lamination workability.

(Viewing angle compensation film)
The viewing angle compensation film is a film for widening the viewing angle so that an image can be seen relatively clearly even when the screen of the liquid crystal display device is viewed from a slightly oblique direction rather than perpendicular to the screen. As such a viewing angle compensation phase difference plate, for example, a retardation film, an alignment film such as a liquid crystal polymer, or an alignment layer such as a liquid crystal polymer supported on a transparent substrate is used. A normal retardation plate uses a birefringent polymer film uniaxially stretched in the plane direction, whereas a retardation plate used as a viewing angle compensation film stretches biaxially in the plane direction. Birefringent polymer film, biaxially stretched film such as polymer with birefringence with a controlled refractive index in the thickness direction that is uniaxially stretched in the plane direction and stretched in the thickness direction, etc. Used. Examples of the inclined alignment film include a film obtained by bonding a heat shrink film to a polymer film and stretching or / and shrinking the polymer film under the action of the contraction force by heating, and a film obtained by obliquely aligning a liquid crystal polymer. Can be mentioned. The raw material polymer for the phase difference plate is the same as the polymer described in the previous phase difference plate, preventing coloration due to a change in the viewing angle based on the phase difference by the liquid crystal cell and expanding the viewing angle for good visual recognition. An appropriate one for the purpose can be used.

  In addition, from the viewpoint of achieving a wide viewing angle with good visibility, an optically compensated phase difference in which an optically anisotropic layer composed of a liquid crystal polymer alignment layer, particularly a discotic liquid crystal polymer gradient alignment layer, is supported by a triacetylcellulose film. A plate can be preferably used.

(Brightness enhancement film)
A polarizing plate obtained by bonding a polarizing plate and a brightness enhancement film is usually provided on the back side of a liquid crystal cell. The brightness enhancement film reflects a linearly polarized light with a predetermined polarization axis or a circularly polarized light in a predetermined direction when natural light is incident due to a backlight such as a liquid crystal display device or reflection from the back side, and transmits other light. In addition, a polarizing plate in which a brightness enhancement film is laminated with a polarizing plate allows light from a light source such as a backlight to enter to obtain transmitted light in a predetermined polarization state, and reflects light without transmitting the light other than the predetermined polarization state. The The light reflected on the surface of the brightness enhancement film is further inverted through a reflective layer or the like provided behind the brightness enhancement film and re-incident on the brightness enhancement film, and part or all of the light is transmitted as light having a predetermined polarization state. Luminance can be improved by increasing the amount of light transmitted through the enhancement film and increasing the amount of light that can be used for liquid crystal display image display or the like by supplying polarized light that is difficult to be absorbed by the polarizer.

  In the present invention, the polarizer, the transparent protective film, the optical film, etc. that form the polarizing plate described above, and the adhesive layer, for example, each include salicylic acid ester compounds, benzophenol compounds, benzotriazole compounds, and cyanoacrylates. It may be a compound having an ultraviolet absorbing ability by a method such as a method of treating with an ultraviolet absorber such as a compound based on nickel or a nickel complex salt compound.

[Image display device]
The polarizing plate or the optical film of the present invention can be preferably used for forming various devices such as a liquid crystal display device. The liquid crystal display device can be formed according to the conventional method. That is, a liquid crystal display device is generally formed by appropriately assembling components such as a liquid crystal cell, a polarizing plate or an optical film, and an illumination system as necessary, and incorporating a drive circuit. There is no limitation in particular except the point which uses the polarizing plate or optical film by invention, and it can apply according to the former. As the liquid crystal cell, any type such as a TN type, an STN type, or a π type can be used.

  An appropriate liquid crystal display device such as a liquid crystal display device in which a polarizing plate or an optical film is disposed on one side or both sides of a liquid crystal cell, or a backlight or a reflector used in an illumination system can be formed. In that case, the polarizing plate or optical film by this invention can be installed in the one side or both sides of a liquid crystal cell. When providing a polarizing plate or an optical film on both sides, they may be the same or different. Further, when forming a liquid crystal display device, for example, a single layer or a suitable part such as a diffusing plate, an antiglare layer, an antireflection film, a protective plate, a prism array, a lens array sheet, a light diffusing plate, a backlight, etc. Two or more layers can be arranged.

  Since the retardation plate and the polarizing plate have a function of polarizing light incident from the outside and reflected by the metal electrode, there is an effect that the mirror surface of the metal electrode is not visually recognized by the polarization action. In particular, the mirror surface of the metal electrode can be completely shielded by configuring the retardation plate with a quarter-wave plate and adjusting the angle formed by the polarization direction of the polarizing plate and the retardation plate to π / 4. .

    EXAMPLES The present invention will be described below with reference to examples, but the present invention is shown below and is not limited to the examples. Note that the following examples and comparative examples were evaluated by the following methods.

[Measuring method]
(Sample preparation for Raman spectrum measurement)
Using a microtome (manufactured by Leica, RM2155), a glass knife (manufactured by Nissin EM Co., Ltd., EM-25A type) is put in the normal direction of the surface of the polarizing plate, and the polarizing plate is cut to have a smooth cross section. A thin piece of polarizing plate having a thickness of about 1 mm was obtained.

(Raman spectrum measurement)
The obtained polarizing plate thin piece attached to a support is placed on a sample stage of a microscopic Raman spectrometer (manufactured by RENISHAW), brought into focus, and subjected to Raman spectrum by an Ar ⁺ laser having an excitation wavelength of 514.5 nm. Measurements were made. The measurement is performed at both ends in the thickness direction of the polarizer at a position of 2 μm from the boundary surface of the polarizer protective film and the polarizer (that is, the surface of the polarizer) in the thickness center direction of the polarizer, and in the center portion in the thickness direction. A total of 3 points were used. Each measurement was performed under the conditions of exposure time: 1 second, number of integrations: 5 times, laser output: 10%, measurement diameter: 2 μm.

From the obtained spectrum, the Raman scattering intensity at the peak top in the range of 105 ± 5 cm ⁻¹ is read, and the scattering intensity (T ₁ ) at the central part in the thickness direction and the average of the scattering intensity at two points at both ends in the thickness direction ( The ratio T ₂ / T ₁ of T ₂ ) was determined.

(Measurement of optical properties)
Using a spectrophotometer with an integrating sphere (manufactured by JASCO Corp., V7100), the single transmittance Ts is obtained, and the surface reflection is removed from the measured value of the single transmittance Ts, thereby correcting the single transmittance Ts (Y). Was calculated.
Further, the dichroic ratio DR of the polarizing plate was calculated by the following formula. In the following formula, Ts (Y) represents the single transmittance (%) corrected for the visibility, and P represents the degree of polarization (%).

[Example 1]
(Preparation of polarizer)
A polyvinyl alcohol film having a polymerization degree of 2400, a saponification degree of 99.9% and a thickness of 75 μm is immersed in warm water (swelling bath) at 30 ° C. and swollen, and the length of the polyvinyl alcohol film is twice the original length. A free end uniaxial stretching was performed. Next, the mixture is immersed in an aqueous solution (dyeing bath) having a concentration of a mixture of iodine and potassium iodide (weight ratio 1:16) of 0.3% by weight so that the polyvinyl alcohol film length becomes three times the original length. The film was dyed while uniaxially stretching at the free end. Thereafter, the film was stretched so that the length of the polyvinyl alcohol film was 4 times the original length while immersed in an aqueous solution (crosslinking bath 1) of 3% by weight of boric acid and 3% by weight of potassium iodide. In an aqueous solution of 4% by weight boric acid and 5% by weight potassium iodide (crosslinking bath 2), the polyvinyl alcohol film was stretched so that its length was 6 times the original length. Thereafter, iodine ion impregnation treatment was performed with an aqueous solution (iodine impregnation bath) of 3% by weight of potassium iodide, and then dried in an oven at 60 ° C. for 4 minutes to obtain a polarizer. The thickness of the obtained polarizer was 28 μm.

  Table 1 shows the immersion time and the draw ratio (the magnification based on the original length and the magnification in each step) in each step.

(Transparent protective film)
A 80 μm thick triacetyl cellulose film (trade name “Fujitac TD80UL” manufactured by Fuji Film Co., Ltd.) was used.

(Preparation of adhesive)
A polyvinyl alcohol resin containing an acetoacetyl group (average polymerization degree 1200, saponification degree 98.5 mol%, acetoacetylation degree 5 mol%) 100 parts by weight, methylol melamine 32 parts by weight, 30 ° C. temperature condition Below, an aqueous adhesive solution was prepared by dissolving in pure water and adjusting the solid content concentration to 3.2 wt%.

(Preparation of polarizing plate)
Using the adhesive, a triacetyl cellulose film was bonded to both sides of a polarizer with a roll bonding machine under a temperature condition of 30 ° C., and then dried at 60 ° C. for 4 minutes to obtain a polarizing plate having a thickness of 188 μm. It was.

[Examples 2-8, Comparative Examples 1-4]
A polarizing plate was obtained in the same manner as in Example 1, except that the dyeing bath immersion time t _B and the crosslinking bath immersion time t _c were changed as shown in Table 1.

    Measurement results of Raman spectra of polarizing plates obtained in Examples and Comparative Examples, and single transmittance with corrected visibility before and after leaving the polarizing plate in a heating and humidifying condition of temperature 60 ° C. and humidity 95% for 250 hours Table 2 shows the change amount ΔTs (Y) of Ts (Y) and the change amount ΔDR (410) of the dichroic ratio DR (410) at a wavelength of 410 nm.

As is clear from Table 2, the maximum peak intensity T ₁ near 105 cm ⁻¹ by Raman spectroscopy at the center of the polarizer in the thickness direction and the vicinity of 105 cm ⁻¹ by Raman spectroscopy at the end in the thickness direction of the polarizer. maximum peak intensity T ₂ and polarizers range some embodiments in the ratio is the invention of, it can be seen that the change in optical properties kicking high temperature and high humidity environment is small, and is excellent in durability.

Claims (5)

A polarizing plate comprising protective films on both sides of a polarizer obtained by staining a polyvinyl alcohol film with iodine, and having a maximum peak intensity T in the range of 105 ± 5 cm ⁻¹ by Raman spectroscopy at the center in the thickness direction of the polarizer cross section. ₁ and a polarizer having a ratio T ₂ / T ₁ of 0.920 to 0.985 of the maximum peak intensity T _{2 in} the range of 105 ± 5 cm ⁻¹ by Raman spectroscopy at the thickness direction end of the polarizer . A method for producing a polarizing plate according to claim 1,
A step of obtaining a polarizer by performing at least an iodine staining step and a crosslinking step in this order on the polyvinyl alcohol film,
A step of laminating a protective film on the obtained polarizer,
And a ratio t _C / t _B of the dye bath immersion time t _B in the iodine dyeing step and the cross bath immersion time t _C in the crosslinking step is 1.30 to 3.90.   The method for producing a polarizing plate according to claim 2, wherein a step of immersing in a solution having a potassium iodide concentration of 1 to 5% by weight is performed after the crosslinking step.   An optical film comprising at least one polarizing plate according to claim 1.   An image display device comprising the polarizing plate according to claim 1 or the optical film according to claim 4.