JP2012008234A - Polarizer and polarization plate - Google Patents

Abstract

The present invention provides a polarizer having excellent dimensional stability and optical durability in a humidified environment without increasing the amount of boric acid.
The polarizer of the present invention satisfies 0.030 ≦ R _pva ≦ 0.040 and has a weight moisture content of 14% or less:
Here, R _pva is R _pva = R _pva = when the refractive index in the direction in which the refractive index is maximum in the plane of the polarizer is nx and the refractive index in the direction orthogonal to the direction in which the refractive index is maximum is ny. It is represented by nx-ny. The polarizing plate of the present invention has such a polarizer and a protective layer disposed on one side of the polarizer.
[Selection] Figure 1

Description

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

  A liquid crystal display device includes a polarizing plate as an essential component due to its display mechanism. As for the polarizing plate, the protective layer is bonded together typically on the both sides of the polarizer which made the polyvinyl alcohol (PVA) type-resin film adsorb | suck a dichroic substance, and was uniaxially stretched. By the way, as the use of liquid crystal display devices expands, there is an increasing demand for thinning and low cost liquid crystal display devices, and thinning and low cost of polarizing plates, which are essential components of liquid crystal display devices. Is desired.

  In order to meet such a demand, a polarizing plate in which a protective layer is provided only on one side of a polarizer has been proposed (Patent Document 1). However, since PVA polarizers are poor in mechanical properties and optical durability, in a polarizing plate provided with a protective layer only on one side, the dimensional change of the polarizer and deterioration of the optical characteristics are likely to occur. Such a problem is remarkable in a humidified environment.

  In order to improve optical durability in a humidified environment, boric acid is typically added to the polarizer. However, in a polarizing plate in which a protective layer is provided only on one side of the polarizer, a polarizing plate having sufficient optical durability cannot be obtained only by adding boric acid. Furthermore, in a polarizing plate in which a protective layer is provided only on one side of the polarizer, the addition of boric acid does not substantially contribute to the improvement of mechanical properties (for example, dimensional stability).

Japanese Patent Laid-Open No. 10-186133

  The present invention has been made to solve the above-described conventional problems, and its object is to have excellent dimensional stability and optical durability in a humidified environment without increasing the amount of boric acid. It is to provide a polarizer.

The polarizer of the present invention satisfies 0.030 ≦ R _pva ≦ 0.040 and has a moisture content of 14% or less. Here, R _pva has a maximum refractive index in the plane of the polarizer. R _pva = nx−ny, where nx is the refractive index in the direction to become and ny is the refractive index in the direction orthogonal to the direction in which the refractive index is maximum.
In a preferred embodiment, the polarizer has a dichroic ratio DR of 160 or more.
According to another aspect of the present invention, a polarizing plate is provided. This polarizing plate includes the above polarizer and a protective layer disposed on one side of the polarizer.
Another polarizing plate of the present invention has the above polarizer and protective layers arranged on both sides of the polarizer.
Still another polarizing plate of the present invention includes the above polarizer, a protective layer disposed on one side of the polarizer, and a retardation layer disposed on the other side of the polarizer.

According to the present invention, R _pva is 0.030 ≦ R _pva ≦ 0.040, and the weight moisture content is 14% or less, so that it is excellent in a humidified environment without increasing the amount of boric acid. A polarizer having dimensional stability and optical durability is obtained.

It is a schematic sectional drawing of the polarizing plate by one Embodiment of this invention. It is a schematic sectional drawing of the polarizing plate by another embodiment of this invention. It is a schematic sectional drawing of the polarizing plate by another embodiment of this invention. It is a graph which shows the result of the humidification cycle test about the polarizer of Examples 1-3 and Comparative Examples 1-5.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to these specific embodiments.

A. Polarizer The polarizer of the present invention satisfies 0.030 ≦ R _pva ≦ 0.040 and has a moisture content of 14% or less. Here, R _pva is, when the wavelength is 1000 nm, the refractive index in the direction in which the refractive index is maximum in the plane of the polarizer is nx, and the refractive index in the direction orthogonal to the direction in which the refractive index is maximum is ny. , R _pva = nx−ny. Furthermore, the weight moisture content is measured as follows: The film to be measured is cut into a size of 100 mm × 100 mm to form a sample film, and the initial weight of the sample film is measured. Subsequently, the sample film is dried at 120 ° C. for 2 hours, the dry weight is measured, and the moisture content is determined by the following formula. In the following formula, the initial weight and the dry weight are average values obtained by measuring three times, respectively.
Moisture content (% by weight) = [(initial weight−dry weight) / initial weight] × 100
R _pva is preferably 0.039 or less, more preferably 0.035 or less. The weight moisture content is preferably 13% or less, and more preferably 12% or less. It is presumed that these properties are simultaneously satisfied by increasing the amount of crystals that do not contribute to the orientation in the polarizer (typically, low orientation). By satisfying these properties simultaneously, the polarizer of the present invention can have excellent dimensional stability and optical durability in a humidified environment without increasing the amount of boric acid. As a result, even when the polarizer of the present invention is used for a polarizing plate provided with a protective layer only on one side of the polarizer, the dimensional change and the optical characteristics are hardly deteriorated, and the practically acceptable dimensional stability and optical properties are improved. Durability can be achieved.

The polarizer of the present invention preferably has a dichroic ratio DR of 160 or more, more preferably 165 to 185, and particularly preferably 175 to 185. The dichroic ratio DR can be obtained from the following equation.
Dichroic ratio DR = log (0.919 / k ₂ ) / log (0.919 / k ₁ )
Here, k ₁ is the transmission axis of the transmittance of the polarizer, k ₂ is the absorption axis direction of the transmittance of the polarizer, the constant 0.919 is the interfacial reflectance.

The polarizer of the present invention has a transmittance (single transmittance) Ts of preferably 43% or more, and more preferably 44% to 47%. The transmittance Ts can be obtained from the following equation.
Transmittance Ts = (k ₁ + k ₂ ) / 2
Here, as described above, k ₁ is the transmittance in the transmission axis direction of the polarizer, and k ₂ is the transmittance in the absorption axis direction of the polarizer.

  The polarizer of the present invention is mainly composed of a polyvinyl alcohol (PVA) resin containing a dichroic substance such as iodine or a dichroic dye.

  The iodine content of the polarizer of the present invention is preferably 1.8% by weight to 5.0% by weight, and more preferably 2.0% by weight to 4.0% by weight. By setting the iodine content in the above range, a polarizing plate having a transmittance in a preferable range can be obtained, and a liquid crystal display device having a high contrast ratio in the front direction can be obtained.

  The boric acid content of the polarizer of the present invention is preferably 0.5% by weight to 3.0% by weight, more preferably 1.0% by weight to 2.8% by weight, particularly in terms of boron. Preferably it is 1.5 weight%-2.6 weight%. As described above, according to the present invention, a polarizer having excellent dimensional stability and optical durability in a humidified environment can be obtained without increasing the amount of boric acid.

  The polarizer of the present invention may preferably further contain potassium. The potassium content is preferably 0.2% by weight to 1.0% by weight, more preferably 0.3% by weight to 0.9% by weight, and particularly preferably 0.4% by weight to 0.00%. 8% by weight. By making potassium content into the said range, the polarizing plate which has the transmittance | permeability of a preferable range and has high polarization degree can be obtained.

  The PVA resin can be obtained by saponifying a vinyl ester polymer obtained by polymerizing a vinyl ester monomer. The saponification degree of the PVA resin is preferably 95.0 mol% to 99.9 mol%. The saponification degree can be determined according to JIS K 6726-1994. By using a PVA resin having a saponification degree in the above range, a polarizer having excellent durability can be obtained.

  As the average degree of polymerization of the PVA-based resin, an appropriate value can be selected according to the purpose. The average degree of polymerization is preferably 1200 to 3600. The average degree of polymerization can be determined according to JIS K 6726-1994.

  The thickness of the polarizer of the present invention is not particularly limited, and an appropriate thickness can be adopted depending on the purpose. The thickness is typically about 1 μm to 80 μm.

B. Method for Producing Polarizer The polarizer of the present invention can be produced by any suitable method. Hereinafter, a preferable example of the method for producing a polarizer of the present invention will be described. This manufacturing method includes performing a dyeing | staining process, a bridge | crosslinking process, an extending process, and a drying process to a polyvinyl alcohol-type resin film. Any appropriate film used in the art can be used as the polyvinyl alcohol-based resin film. As the polyvinyl alcohol-based resin film, for example, a film formed from a polyvinyl alcohol-based resin as described in the above section A can be used.

  In the dyeing step, iodine or dichroic dye is adsorbed and oriented on the polyvinyl alcohol resin film. Dyeing is usually performed by immersing the polyvinyl alcohol resin film in a dyeing solution (dyeing bath). As the staining solution, an iodine solution is generally used. The iodine concentration in the iodine solution is preferably 0.01% by weight to 1% by weight, more preferably 0.02% by weight to 0.5% by weight. When the iodine concentration is in such a range, the desired iodine content can be realized in the obtained polarizer. In the dyeing step, the temperature of the iodine solution is usually about 20 ° C to 50 ° C, preferably 25 ° C to 40 ° C. The immersion time in the iodine solution is usually 10 seconds to 300 seconds, preferably 20 seconds to 240 seconds.

  In the dyeing step, stretching can be performed as necessary. By performing stretching in the dyeing process, the stretching ratio in the stretching process described later can be reduced, and the film can be prevented from being broken. The draw ratio in the dyeing step is usually 6.5 times or less, preferably 1.2 times to 6.5 times, more preferably 2 times to 4 times, particularly preferably with respect to the original length of the polyvinyl alcohol resin film. Is 2 to 3 times. If the stretching ratio in the dyeing process is too large, the stretching ratio in the stretching process becomes too small, so that sufficient optical properties may not be obtained particularly when the stretching process is performed after the crosslinking process. Although not theoretically obvious, it is presumed that a polarizer having a desired dichroic ratio and transmittance can be obtained by stretching at a predetermined magnification in the dyeing process.

  In the crosslinking step, a boron compound is usually used as a crosslinking agent. The order of the crosslinking steps is not particularly limited. The crosslinking step can be performed together with the stretching step. The crosslinking step can be performed multiple times. Examples of the boron compound include boric acid and borax. Boron compounds are usually used in the form of an aqueous boric acid solution. The boric acid concentration of the boric acid aqueous solution is about 2 to 15% by weight, preferably 3 to 13% by weight. When the boric acid concentration is in such a range, heat resistance and the like can be efficiently imparted to the obtained polarizer by the crosslinking treatment. The boric acid aqueous solution may contain an iodide compound such as potassium iodide. Crosslinking is usually performed by immersing the polyvinyl alcohol resin film in an aqueous boric acid solution (crosslinking bath). Alternatively, a boron compound may be applied to the polyvinyl alcohol resin film by a coating method, a spraying method, or the like. The processing temperature in a bridge | crosslinking process is 25 degreeC or more normally, Preferably it is 30 to 85 degreeC, More preferably, it is 30 to 60 degreeC. The treatment time is usually 5 seconds to 800 seconds, preferably 8 seconds to 500 seconds.

  In the stretching step, the polyvinyl alcohol-based resin film is usually subjected to uniaxial stretching. The stretching process can be performed together with the dyeing process and / or the crosslinking process. As the stretching method, either wet stretching or dry stretching can be employed. In wet stretching, stretching is generally performed after the dyeing step. Or it can extend | stretch with a bridge | crosslinking process. In dry stretching, examples of the stretching means include an inter-roll stretching method, a heated roll stretching method, and a compression stretching method. In the stretching means, the unstretched film is usually heated. The stretching process can be performed in multiple stages.

  In the wet stretching, an iodide compound can be contained in the treatment liquid (stretching bath) used. In this case, the iodide compound concentration is preferably 0.1 wt% to 10 wt%, more preferably 0.2 wt% to 5 wt%. The treatment temperature in the wet stretching is usually 25 ° C or higher, preferably 30 ° C to 85 ° C, more preferably 30 ° C to 60 ° C. The immersion time is usually 10 seconds to 800 seconds, preferably 30 seconds to 500 seconds.

  The total draw ratio by stretching is preferably 3 to 17 times, more preferably 4 to 10 times, and particularly preferably 4 to 8 times the original length of the polyvinyl alcohol-based resin film. The “total draw ratio” refers to a cumulative draw ratio including stretching in those steps when stretching is involved in a step other than the stretching step (for example, a swelling step described later). When the total draw ratio is too low, the orientation is insufficient and a polarizer having high optical properties (typically, the degree of polarization) is often not obtained. If the total draw ratio is too high, the film is likely to break during stretching, and the resulting polarizer becomes too thin, and the workability in the subsequent process may be reduced.

  In the method for producing a polarizer of the present invention, typically, a swelling step can be performed before the dyeing step. The swelling is usually performed by immersing the polyvinyl alcohol resin film in a treatment liquid (swelling bath). By swelling the polyvinyl alcohol-based resin film, not only the surface of the polyvinyl alcohol-based resin film can be cleaned of stains and anti-blocking agents, but also there is an effect of preventing unevenness such as uneven dyeing. As the treatment liquid, water, distilled water, or pure water is usually used. If the main component is water, the treatment liquid may contain an iodide compound, an additive such as a surfactant, alcohol, and the like. The treatment temperature in the swelling step is usually 20 ° C to 45 ° C, preferably 25 ° C to 40 ° C. The immersion time is usually 10 seconds to 300 seconds, preferably 20 seconds to 240 seconds. In the swelling step, it is preferable to uniformly swell the polyvinyl alcohol resin film. Uneven staining can be prevented by uniformly swelling the film.

  In the swelling step, stretching can be performed as necessary. By performing stretching in the swelling process, the stretching ratio in the stretching process can be reduced, and the film can be prevented from being broken. The draw ratio in the swelling step is usually 6.5 times or less, preferably 1.2 times to 6.5 times, more preferably 2 times to 4 times, particularly preferably with respect to the original length of the polyvinyl alcohol resin film. Is 2 to 3 times. If the stretching ratio in the swelling process becomes too large, the stretching ratio in the stretching process becomes too small. Therefore, particularly when the stretching process is performed after the crosslinking process, sufficient optical properties may not be obtained.

  In the manufacturing method of the polarizer of this invention, a metal ion process can be performed as needed. The metal ion treatment is performed by immersing the polyvinyl alcohol-based resin film in an aqueous solution containing a metal salt. Various metal ions (typically, metal ions of transition metals such as cobalt, nickel, zinc, chromium, aluminum, copper, manganese, and iron) may be included in the polyvinyl alcohol-based resin film by metal ion treatment. it can. The step of performing the metal ion treatment is not particularly limited, and can be performed at any appropriate time in the production method. Further, the metal ion treatment may be performed simultaneously with the dyeing step, the crosslinking step and / or the stretching step by allowing a metal salt to coexist in the dyeing bath, the crosslinking bath and / or the stretching bath.

  In the method for producing a polarizer of the present invention, typically, a cleaning step can be performed at any appropriate point before the drying step. Typically, the washing step is performed after the dyeing step, the crosslinking step, and the stretching step. In the washing step, typically, the polyvinyl alcohol-based resin film is immersed in a potassium iodide solution and washed. The potassium iodide concentration in the potassium iodide solution is usually 0.5 wt% to 10 wt%, preferably 0.5 wt% to 8 wt%, more preferably 1 wt% to 6 wt%. The treatment temperature in the washing step with the potassium iodide solution is usually 15 ° C to 60 ° C, preferably 25 ° C to 40 ° C. The treatment time (immersion time) is usually 1 second to 120 seconds, preferably 3 seconds to 90 seconds.

  Alternatively, in the washing step, the polyvinyl alcohol-based resin film may be washed by immersing it in water (typically pure water such as ion-exchanged water or distilled water). The treatment temperature in the washing step with water is usually 5 ° C to 50 ° C, preferably 10 ° C to 45 ° C, more preferably 15 ° C to 40 ° C. The treatment time (immersion time) is usually 10 seconds to 300 seconds, preferably 20 seconds to 240 seconds. The washing step with water may be combined with the washing step with the potassium iodide solution. Further, a liquid alcohol such as methanol, ethanol, isopropyl alcohol, butanol, propanol or the like may be appropriately added to water to form a cleaning liquid.

After performing the said dyeing process, a bridge | crosslinking process, an extending | stretching process, and arbitrary processing processes as needed, the polarizer of this invention is obtained by using the said polyvinyl alcohol-type resin film for a drying process. Typically, since the dyeing step, the crosslinking step, the stretching step, and the like are continuously performed, the drying step can also be performed continuously from the respective steps. In the present invention, the drying step is performed so that the obtained polarizer has an R _pva of 0.040 or less and a moisture content of 14% or less. Details will be described below.

  The weight moisture content of the polyvinyl alcohol-based resin film before the drying step is preferably 25% to 55% by weight, more preferably 27% to 52% by weight, and particularly preferably 30% to 50% by weight. If the weight moisture content before drying is in such a range, a polarizer having a desired weight moisture content can be efficiently obtained by appropriately selecting the drying conditions. The weight moisture content before drying can be controlled by adjusting the immersion time of the film in the treatment bath in each of the above steps.

As the drying conditions in the drying step, any appropriate conditions can be adopted as long as R _pva of the obtained polarizer can be _controlled to 0.030 ≦ R _pva ≦ 0.040 and the weight moisture content can be controlled to 14% or less.

In one embodiment, the drying process is performed in two stages. Preferably, a drying process includes the 1st drying process dried at low temperature (for example, 25 to 65 degreeC), and the 2nd drying process dried at high temperature (for example, 65 to 115 degreeC). By performing two-stage drying employing such specific conditions, a polarizer having the desired R _pva , weight moisture content, dichroic ratio DR, and transmittance Ts as described above can be obtained. Although it is not theoretically obvious, a film having such a low weight moisture content in the second drying step can be obtained by reducing the weight moisture content of the film to the vicinity of the desired weight moisture content by the first drying step. It is presumed that by heating at a high temperature, water in the film is further lost and high crystallization or crosslinking is realized. More preferably, the first drying step is performed while suppressing shrinkage in the width direction of the film. As a means for suppressing shrinkage in the width direction of the film in the first drying step, roll conveyance is typically mentioned. Suppressing shrinkage in the width direction in the first drying step has a synergistic effect with realizing high crystallization in the second drying step, and has excellent dimensional stability and optics in a humidified environment. It is presumed that a polarizer having high durability can be obtained. In another embodiment, the drying is performed at a high temperature (eg, 70 ° C. to 110 ° C.) and in one step. When performing such high temperature and one-step drying, it is preferable that the film is also stretched in the dyeing process in addition to the stretching process. Although not theoretically obvious, a polarizer having the desired characteristics can be obtained by combining such high-temperature drying and stretching in the dyeing process.

  As described above, the polarizer of the present invention can be manufactured. Of the specific operations and conditions in the method for producing a polarizer of the present invention that are not described in this specification, the operations described in JP2009-48179A and JP2009-163202A are described. Or general conditions or conditions in the industry may be employed.

C. Polarizing Plate FIG. 1 is a schematic cross-sectional view of a polarizing plate according to one embodiment of the present invention. The polarizing plate 100 includes a polarizer 10 and a protective layer 20 disposed on one side of the polarizer 10. The polarizer 10 is the polarizer of the present invention described in the above items A and B. As described in the above items A and B, the polarizer of the present invention has excellent dimensional stability and optical durability in a humidified environment. Therefore, a polarizing plate provided with a protective layer only on one side of the polarizer The effect is remarkable when it is used. That is, as in the illustrated example, even in a polarizing plate in which a protective layer is provided only on one side of the polarizer, the polarizer of the present invention hardly undergoes dimensional change and deterioration of optical characteristics, and has practically acceptable dimensional stability. And optical durability can be realized. Of course, the polarizer of the present invention is not only a polarizing plate provided with a protective layer only on one side of the polarizer, but also a polarizing plate provided with protective layers 20 and 30 on both sides of the polarizer 10 as shown in FIG. It can be suitably used. Furthermore, as shown in FIG. 3, it can be suitably used for a polarizing plate in which the protective layer 20 is provided on one side of the polarizer 10 and the retardation layer 40 is provided on the other side.

  The protective layers 20 and 30 are formed of any appropriate film that can be used as a protective layer for a polarizing plate. Specific examples of the material that is the main component of the film include cellulose resins such as triacetyl cellulose (TAC), polyester-based, polyvinyl alcohol-based, polycarbonate-based, polyamide-based, polyimide-based, polyethersulfone-based, and polysulfone-based materials. And transparent resins such as polystyrene, polynorbornene, polyolefin, (meth) acryl, and acetate. Further, thermosetting resins such as (meth) acrylic, urethane-based, (meth) acrylurethane-based, epoxy-based, and silicone-based or ultraviolet curable resins are also included. In addition to this, for example, a glassy polymer such as a siloxane polymer is also included. Moreover, the polymer film as described in Unexamined-Japanese-Patent No. 2001-343529 (WO01 / 37007) can be used. As a material for this film, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted imide group in the side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and nitrile group in the side chain For example, a resin composition having an alternating copolymer composed of isobutene and N-methylmaleimide and an acrylonitrile / styrene copolymer can be mentioned. The polymer film can be, for example, an extruded product of the resin composition.

  The protective layer (outer protective layer) 20 may be subjected to any appropriate surface treatment on the surface thereof. For example, as the protective layer, a commercially available polymer film subjected to surface treatment can be used as it is. Alternatively, a commercially available polymer film can be used after any surface treatment. Examples of the surface treatment include diffusion treatment (antiglare treatment), antireflection treatment (antireflection treatment), hard coat treatment, and antistatic treatment. Furthermore, / or a surface treatment layer may be provided outside the protective layer 20 (on the side opposite to the polarizer 10). Any appropriate layer can be adopted as the surface treatment layer depending on the purpose. For example, a diffusion treatment (antiglare treatment) layer, an antireflection treatment (antireflection treatment) layer, a hard coat treatment layer, an antistatic treatment layer and the like can be mentioned. These surface treatment layers are used for the purpose of preventing the screen from being soiled or damaged, or preventing the display image from becoming difficult to see due to the reflection of indoor fluorescent light or sunlight on the screen. In general, the surface treatment layer is obtained by fixing the treatment agent for forming the treatment layer on the surface of the base film. The base film may also serve as the protective layer. Furthermore, the surface treatment layer may have a multilayer structure in which, for example, a hard coat treatment layer is laminated on the antistatic treatment layer.

  The protective layer (inner protective layer) 30 is preferably optically isotropic. Specifically, the thickness direction retardation Rth (550) of the inner protective layer is preferably −20 nm to +20 nm, more preferably −10 nm to +10 nm, particularly preferably −6 nm to +6 nm, and most preferably −3 nm to +3 nm. It is. The in-plane retardation Re (550) of the inner protective layer is preferably 0 nm or more and 10 nm or less, more preferably 0 nm or more and 6 nm or less, and particularly preferably 0 nm or more and 3 nm or less. Details of the film that can form such an optically isotropic protective layer are described in Japanese Patent Application Laid-Open No. 2008-180961, and the description thereof is incorporated herein by reference.

  Any appropriate retardation film can be used as the retardation layer 40. The optical properties (for example, refractive index ellipsoid), the number, the arrangement order when a plurality of retardation films are used, and the like can be appropriately selected according to the purpose, application, configuration of the liquid crystal display device in which the polarizing plate is used, and the like. .

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited by these Examples. Evaluation methods in the examples are as follows. Unless otherwise specified, “parts” and “%” in the examples are based on weight.

(1) R _pva
About the polarizer obtained by the Example and the comparative example, it measured using the near-infrared phase difference measuring apparatus KOBRA-31X100 / IR (wavelength 1000nm, 23 degreeC) by Oji Scientific Instruments.

(2) Weight moisture content The polarizers obtained in Examples and Comparative Examples were cut into a size of 100 mm × 100 mm to obtain a sample film, and the initial weight of the sample film was measured. Subsequently, the sample film was dried at 120 ° C. for 2 hours, the dry weight was measured, and the moisture content was determined by the following formula. In the following formula, the initial weight and the dry weight were measured three times, and the average value was adopted.
Moisture content (% by weight) = {(initial weight−dry weight) / initial weight} × 100

(3) Dichroic ratio DR of polarizer
For the polarizers obtained in the examples and comparative examples, the transmittance k _{1 in} the transmission axis direction and the transmittance k ₂ in the absorption axis direction were measured using a spectrophotometer V7100, and the dichroic ratio DR was calculated from the following equation. Was calculated:
Dichroic ratio DR = log (0.919 / k ₂ ) / log (0.919 / k ₁ )
Here, the constant 0.919 is the interface reflectance.

(4) Humidification cycle test The polarizers obtained in the examples and comparative examples were changed from 5% to 95% in the first hour at a temperature of 40 ° C. and from 95% to 5% in the next hour. Placed in a changing environment. The dimensional change in the width direction of the polarizer accompanying the change in humidity was continuously observed and graphed. Furthermore, the case where the maximum dimensional change in the width direction (TD) of the polarizer was 250% or less was determined to be OK, and the case where it exceeded 250% was determined to be NG.

<Example 1>
A PVA resin film having a polymerization degree of 2400, a saponification degree of 99.7 mol%, and a thickness of 75 μm was prepared. The film was stretched 3 times in the film transport direction while being dyed in an aqueous iodine solution at 30 ° C., and then the total draw ratio was 4% by weight boric acid at 60 ° C. and 5% by weight potassium iodide aqueous solution. The film was stretched to be 6 times the original length. Furthermore, the stretched film was washed by immersing it in a 2 wt% potassium iodide aqueous solution at 30 ° C. for several seconds. The obtained stretched film was dried at 90 ° C. to obtain a polarizer. The obtained polarizer was subjected to the evaluations (1) to (3) above. The results are shown in Table 1. Further, the obtained polarizer was subjected to the humidification cycle test of (4) above. The results are shown in Table 1 and FIG.
Next, using a PVA adhesive, a protective film was bonded to one side of the obtained polarizer, and a retardation film was bonded to the other side to obtain a laminate. This laminate was dried at 40 ° C. for 2 minutes, and then an adhesive was laminated on the outside of the retardation film to obtain a polarizing plate.

<Example 2>
A polarizer was obtained in the same manner as in Example 1 except that drying was performed at 80 ° C. The obtained polarizer was subjected to the evaluations (1) to (3) above. The results are shown in Table 1. Further, the obtained polarizer was subjected to the humidification cycle test of (4) above. The results are shown in Table 1 and FIG. Further, a polarizing plate was obtained in the same manner as in Example 1 except that this polarizer was used.

<Example 3>
A polarizer was obtained in the same manner as in Example 1 except that drying was performed at 70 ° C. The obtained polarizer was subjected to the evaluations (1) to (3) above. The results are shown in Table 1. Further, the obtained polarizer was subjected to the humidification cycle test of (4) above. The results are shown in Table 1 and FIG. Further, a polarizing plate was obtained in the same manner as in Example 1 except that this polarizer was used.

<Comparative Example 1>
A polarizer was obtained in the same manner as in Example 1 except that drying was performed at 60 ° C. The obtained polarizer was subjected to the evaluations (1) to (3) above. The results are shown in Table 1. Further, the obtained polarizer was subjected to the humidification cycle test of (4) above. The results are shown in Table 1 and FIG. Further, a polarizing plate was obtained in the same manner as in Example 1 except that this polarizer was used.

<Comparative example 2>
A polarizer was obtained in the same manner as in Example 1 except that drying was performed at 50 ° C. The obtained polarizer was subjected to the evaluations (1) to (3) above. The results are shown in Table 1. Further, the obtained polarizer was subjected to the humidification cycle test of (4) above. The results are shown in Table 1 and FIG. Further, a polarizing plate was obtained in the same manner as in Example 1 except that this polarizer was used.

<Comparative Example 3>
A polarizer was obtained in the same manner as in Example 1 except that drying was performed at 40 ° C. The obtained polarizer was subjected to the evaluations (1) to (3) above. The results are shown in Table 1. Further, the obtained polarizer was subjected to the humidification cycle test of (4) above. The results are shown in Table 1 and FIG. Further, a polarizing plate was obtained in the same manner as in Example 1 except that this polarizer was used.

<Comparative example 4>
A polarizer was obtained in the same manner as in Example 1 except that drying was performed at 35 ° C. The obtained polarizer was subjected to the evaluations (1) to (3) above. The results are shown in Table 1. Further, the obtained polarizer was subjected to the humidification cycle test of (4) above. The results are shown in Table 1 and FIG. Further, a polarizing plate was obtained in the same manner as in Example 1 except that this polarizer was used.

<Comparative Example 5>
A polarizer was obtained in the same manner as in Example 1 except that drying was performed at 30 ° C. The obtained polarizer was subjected to the evaluations (1) to (3) above. The results are shown in Table 1. Further, the obtained polarizer was subjected to the humidification cycle test of (4) above. The results are shown in Table 1 and FIG. Further, a polarizing plate was obtained in the same manner as in Example 1 except that this polarizer was used.

<Evaluation>
As is clear from Table 1, the polarizers of the examples of the present invention are excellent in both the dichroic ratio and the dimensional stability in the humidification cycle test. In particular, as apparent from FIG. 4, the polarizer of the example of the present invention has much superior dimensional stability in the humidification cycle test as compared with the polarizer of the comparative example. Thus, it was confirmed that a polarizer having excellent dimensional stability and optical durability in a humidified environment can be obtained by optimizing R _pva and weight moisture content.

  The polarizer and polarizing plate of the present invention can be suitably used for a liquid crystal display device.

DESCRIPTION OF SYMBOLS 10 Polarizer 20 Protective layer 30 Protective layer 40 Retardation layer 100, 101, 102 Polarizing plate

Claims (5)

A _polarizer satisfying 0.030 ≦ R _pva ≦ 0.040 and having a weight moisture content of 14% or less:
Here, R _pva is R _pva = R _pva = when the refractive index in the direction in which the refractive index is maximum in the plane of the polarizer is nx and the refractive index in the direction orthogonal to the direction in which the refractive index is maximum is ny. It is represented by nx-ny.   The polarizer of Claim 1 whose dichroic ratio DR is 160 or more.   A polarizing plate comprising the polarizer according to claim 1 and 2 and a protective layer disposed on one side of the polarizer.   A polarizing plate comprising the polarizer according to claim 1 or 2 and protective layers disposed on both sides of the polarizer. A polarizing plate comprising the polarizer according to claim 1, a protective layer disposed on one side of the polarizer, and a retardation layer disposed on the other side of the polarizer.

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