JPWO2017078095A1 - Manufacturing method of polarizer - Google Patents

Abstract

The degree of orientation is 0.250 to 0.400, the contraction force in the absorption axis direction is 3.5 N / 2 mm or less, and the degree of orientation is a polarizer obtained from Equation 1 below: , AMD is the absorbance of infrared light polarized in the direction of the absorption axis of the polarizer, ATD is the absorbance of infrared light polarized in the direction of the transmission axis of the polarizer, and Alage is the higher of AMD and ATD Absorbance, and Asmall is the lower of AMD and ATD).

Description

  The present invention relates to a polarizer and a method for producing the same, and more particularly to a polarizer having excellent optical characteristics and a small shrinkage force in the absorption axis (stretching) direction and a method for producing the same.

  Polarizers used in various image display devices such as liquid crystal display devices (LCD), electroluminescence (EL) display devices, plasma display devices (PDP), field emission display devices (FED), OLEDs, etc. In particular, a polyvinyl alcohol (PVA) film includes a polarizer in which an iodine compound or a dichroic polarizing material is adsorbed and oriented, and a polarizer protective film is sequentially laminated on one surface of the polarizer. The other surface of the child has a multilayer structure in which a polarizer protective film, an adhesive layer bonded to another member, and a release film are sequentially laminated.

  A polarizer constituting a polarizing plate is applied to an image display device, and is basically required to have both high transmittance and degree of polarization in order to provide an image having excellent color reproducibility. In order to embody this, a polarizer was manufactured by modifying the polyvinyl alcohol film itself or using a non-sublimation dichroic dye in place of the sublimable iodine polarization element.

  On the other hand, a polarizer usually has a polarizing function by orienting an internal molecular arrangement in a predetermined direction by stretching a film for forming a polarizer produced using a polymer. Therefore, the stretching process is an indispensable process when manufacturing a polarizer.

  However, such a stretching process causes the contraction force in the stretching (absorption axis) direction to be expressed later when the polarizer is placed in a predetermined environment, and the contraction force in the absorption axis direction is Cause deformation of the polarizer. Therefore, reducing the contraction force in the direction of the absorption axis is an important consideration in manufacturing an improved polarizer.

  However, a polarizer that has realized both a high degree of polarization and a low contraction force has not been known so far.

  Japanese Laid-Open Patent Publication No. 2010-145866 discloses a method for manufacturing a polarizer having a small shrinkage stress, but cannot provide a satisfactory alternative to the above problem.

JP 2010-145866 A

  An object of the present invention is to provide a polarizer having a small degree of contraction in the absorption axis direction while having an excellent degree of polarization, and a method for producing the same.

（式中、Ａ_ＭＤは偏光子の吸収軸方向に偏光する赤外光の吸光度であり、Ａ_ＴＤは偏光子の透過軸方向に偏光する赤外光の吸光度であり、Ａ_{ｌａｒｇｅ}はＡ_ＭＤとＡ_ＴＤのうちの高い方の吸光度であり、Ａ_{ｓｍａｌｌ}はＡ_ＭＤとＡ_ＴＤのうちの低い方の吸光度である）。1. The degree of orientation is 0.250 to 0.400, the contraction force in the absorption axis direction is 3.5 N / 2 mm or less,
The degree of orientation is a polarizer obtained from Equation 1 below:

(Wherein, A _MD is the absorbance of infrared light polarized in the absorption axis direction of the polarizer, A _TD is the absorbance of infrared light polarized in the transmission axis direction of the polarizer, A _large is the A _MD the absorbance of the higher one of _{a TD,} a _small the absorbance of the lower of _{a MD} and _{a TD).}

  2. 2. The polarizer according to 1 above, wherein the degree of orientation is 0.300 to 0.400.

3. Including swelling, dyeing, stretching, cross-linking, complementary color and drying steps of the polarizer-forming film,
The cross-linking step includes a first cross-linking step of stretching the polarizer forming film to 2.00 to 3.00 times, and a first forming step of stretching the polarizer forming film to 1.00 times or less after the first cross-linking step. 2 cross-linking steps,
In the complementary color step, the polarizer forming film is stretched at a stretch ratio that is higher than the stretch ratio of the second cross-linking step and lower than the stretch ratio of the first cross-linking step.

  4). 4. The method for producing a polarizer according to 3 above, wherein in the second crosslinking step, the polarizer-forming film is stretched by 0.85 to 1.00 times.

  5. The method for producing a polarizer according to 3 or 4 above, wherein in the complementary color step, the film for forming a polarizer is stretched by 1.01 to 1.25 times.

  6). A polarizing plate comprising the polarizer according to 1 or 2 and a polarizer protective film bonded to at least one surface of the polarizer.

  7). 7. An image display device comprising the polarizing plate as described in 6 above.

  The polarizer of the present invention exhibits a small contraction force in the absorption axis direction while having excellent optical characteristics without deterioration of other physical properties by having an orientation degree in a predetermined range and a contraction force in the absorption axis direction. be able to.

  In the method for producing a polarizer of the present invention, the polarizer according to the present invention can be produced by stretching the film for forming a polarizer at a stretching ratio in a specific range in the crosslinking step and the complementary color step. Usually, the higher the degree of stretching, the higher the degree of orientation. In order to realize excellent polarization characteristics, it is necessary to increase the stretching ratio. On the other hand, the higher the stretching ratio, the greater the contraction force in the stretching (absorption axis) direction. . Therefore, there is a trade-off relationship between the realization of a high degree of orientation and the contraction force in the low absorption axis direction. So far, a polarizer that has realized both a high degree of orientation and a contraction force in the low absorption axis direction has been described. Although not known, in particular, the method for producing a polarizer of the present invention can adjust the range of the degree of orientation while having a low shrinkage force in the absorption axis direction, and as a result, while having a high degree of polarization. A polarizer having a small contraction force in the absorption axis direction can be manufactured.

  In the present invention, the degree of orientation is 0.250 to 0.400, and the contraction force in the absorption axis direction is 3.5 N / 2 mm or less, so that the polarizer has excellent optical characteristics and small contraction force in the absorption axis direction. And a manufacturing method thereof.

  Hereinafter, the present invention will be described in detail.

  As described above, it has been conventionally known that a high degree of orientation of a polarizer and a small contraction force in the absorption axis direction are in a trade-off relationship. There are no known examples of children.

  However, the inventors of the present application manufactured a polarizer that simultaneously satisfies a high degree of orientation and a small contraction force in the direction of the absorption axis through a method for manufacturing a polarizer capable of adjusting the degree of orientation. In addition, when the degree of orientation and the contraction force in the absorption axis direction are adjusted within a specific range, a polarizer having a small contraction force in the absorption axis direction can be obtained without a decrease in the polarization degree.

The polarizer of the present invention may have an orientation degree of 0.250 to 0.400, preferably 0.300 to 0.400. If the degree of orientation is less than 0.250, the degree of polarization decreases, and if it exceeds 0.400, there is a problem that the contraction force in the absorption axis direction increases and the warpage of the polarizer increases.
In the present invention, in order to adjust the degree of orientation to the above range, the stretching ratio in the first crosslinking step is controlled to 2.00 to 3.00 times and the total cumulative stretching ratio is controlled to 5.0 times or more. Can be adjusted.

  The degree of orientation according to the present invention is the difference between the absorbance of infrared light (IR) polarized in the absorption axis direction (MD direction) of the polarizer and the absorbance of infrared light polarized in the transmission axis direction (TD direction) of the polarizer. Can be obtained from A specific relational expression for obtaining a specific degree of orientation is as shown in Equation 1 below.

（式中、Ａ_ＭＤは偏光子の吸収軸方向（ＭＤ方向）に偏光する赤外光の吸光度であり、Ａ_ＴＤは偏光子の透過軸方向（ＴＤ方向）に偏光する赤外光の吸光度であり、Ａ_{ｌａｒｇｅ}はＡ_ＭＤとＡ_ＴＤのうちの高い方の吸光度であり、Ａ_{ｓｍａｌｌ}はＡ_ＭＤとＡ_ＴＤのうちの低い方の吸光度である）。
赤外光の吸光度は、たとえば、フーリエ変換赤外分光光度計（ＦＴ−ＩＲ）で測定することができる。赤外光の波数は、たとえば、１２９０ｃｍ^−１とすることができる。

(In the formula, _AMD is the absorbance of infrared light polarized in the absorption axis direction (MD direction) of the polarizer, and A _TD is the absorbance of infrared light polarized in the transmission axis direction (TD direction) of the polarizer). _{There, a large} is the absorbance of the higher one of _{a MD} and _{a TD, a small} the absorbance of the lower of _{a MD} and _{a TD).}
The absorbance of infrared light can be measured by, for example, a Fourier transform infrared spectrophotometer (FT-IR). The wave number of infrared light can be set to 1290 cm ⁻¹ , for example.

  The polarizer of the present invention may have a low contraction force in the absorption axis direction, and the contraction force in the absorption axis direction may be 3.5 N / 2 mm or less. When the contraction force in the absorption axis direction is 3.5 N / 2 mm or less, deformation of the polarizer can be effectively prevented. The lower the shrinkage force in the absorption axis direction, the better. Therefore, the lower limit thereof is not particularly limited, and may be, for example, 2 N / 2 mm or more, 1 N / 2 mm or more, or 0.1 N / 2 mm or more. In the present invention, in order to adjust the contraction force in the absorption axis direction of the polarizer to the above range, the stretching ratio of the first crosslinking step is 2.00 to 3.00 times, and the stretching ratio of the second crosslinking step is 1. It is possible to adjust by controlling at less than 0.000 times.

  The polarizer of the present invention may have a thickness of 5 to 30 μm, preferably 10 to 28 μm, more preferably 15 to 26 μm. When the thickness of the polarizer is in the above range, both low shrinkage force in the absorption axis direction of the polarizer and handling properties can be achieved.

  The present invention also provides a method for manufacturing the above-described polarizer.

  The method for producing a polarizer of the present invention includes swelling, dyeing, stretching, cross-linking, complementary color and drying steps of a polarizer-forming film, and the cross-linking step is 2.00 to 3.00 times the polarizer-forming film. A first cross-linking step for stretching the film, and a second cross-linking step for relieving stress by stretching the polarizer-forming film to 1.00 times or less after the first cross-linking step. The film for forming a polarizer is stretched at a stretch ratio that is higher than the stretch ratio of the cross-linking step and lower than the stretch ratio of the first cross-linking step. By adjusting the stretching ratio of the crosslinking step and the complementary color step as described above, the degree of orientation of the polarizer and the contraction force in the absorption axis direction can be adjusted to realize a high polarization degree and a small contraction force in the absorption axis direction.

  The manufacturing method of the polarizer of the present invention will be described more specifically as follows.

  As long as the film for forming a polarizer for producing a polarizer is a polymer film used for producing a polarizing plate, a film that can be dyed with a dichroic substance (for example, iodine) known in the art is not particularly limited. For example, polyvinyl alcohol film, partially saponified polyvinyl alcohol film; polyethylene terephthalate film, ethylene-vinyl acetate copolymer film, ethylene-vinyl alcohol copolymer film, cellulose film, these partially A hydrophilic polymer film such as a saponified film, or a polyene oriented film such as a dehydrated polyvinyl alcohol film or a dehydrochlorinated polyvinyl chloride film can be used. Among these, a polyvinyl alcohol film is preferable because it not only has an excellent effect of enhancing the uniformity of the degree of polarization in the plane, but also has an excellent dyeing affinity for iodine.

  The method for producing a polarizer according to the present invention may include a swelling step, a dyeing step, a crosslinking step, a complementary color step, a stretching step, a washing step and a drying step, and can be classified according to the stretching method. For example, a dry stretching method, a wet stretching method, or a hybrid stretching method in which the above-mentioned two kinds of stretching methods are mixed can be used. Below, although the manufacturing method of the polarizer of this invention is demonstrated taking the wet extending | stretching method as an example, it is not restrict | limited to this.

  Among the above steps, the remaining steps except the drying step are the states in which the film for forming the polarizer is immersed in a constant temperature bath (bath) filled with one or more solutions each selected from various types of solutions. Can be done.

<Swelling step>
The swelling step is performed by immersing the unstretched polarizer-forming film in a swelling tank filled with a swelling aqueous solution before dyeing it, and depositing impurities on the surface of the polarizer-forming film, such as impurities or antiblocking agents. Are steps for swelling the polarizer forming film, improving the stretching efficiency, preventing uneven dyeing, and improving the physical properties of the polarizer.

  As the aqueous solution for swelling, an aqueous solution for swelling known in the art can be used without particular limitation. For example, water (pure water, deionized water) may be used alone, and a small amount of glycerin or potassium iodide may be used. When is added, processability can be improved along with swelling of the polymer film. The content of glycerin is preferably 5% by weight or less and the content of potassium iodide is preferably 10% by weight or less with respect to 100% by weight of water.

  The temperature of the swelling tank is not particularly limited, but may be 20 to 45 ° C., for example, 25 to 40 ° C.

  As the performance time of the swelling step (swelling time in the swelling tank), a performance time known in the art can be applied without particular limitation, and may be, for example, 180 seconds or less, preferably 90 seconds or less. . When the immersion time is in the above range, it is possible to suppress the swelling from becoming excessively saturated, and the breakage due to the softening of the polarizer forming film is prevented, and the adsorption of iodine becomes uniform in the dyeing step. The degree of polarization can be improved.

  The stretching step can be performed together with the swelling step. At this time, the stretching ratio may be about 1.1 to 3.5 times, but is not limited, and preferably 1.5 to 3.0 times. Good. If the draw ratio is less than 1.1 times, wrinkles may occur. If it exceeds 3.5 times, the initial optical characteristics may be weak.

<Dyeing step>
The dyeing step is a step of immersing the polarizer forming film in a dyeing tank filled with a dichroic substance, for example, an aqueous dyeing solution containing iodine, and adsorbing iodine to the polarizer forming film.

  As the aqueous dye solution, an aqueous dye solution known in the art can be used without particular limitation, and water, a water-soluble organic solvent, or a mixed solvent thereof and iodine can be contained. The iodine content may be 0.4 to 400 mmol / L in the aqueous dyeing solution, but is not limited thereto, and is preferably 0.8 to 275 mmol / L, most preferably 1 to 200 mmol / L. Also good.

  The aqueous dyeing solution may further contain an iodide as a solubilizing agent so that the dyeing efficiency can be improved. As the iodide, an iodide known in the art can be used without limitation. For example, potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, iodide At least one selected from the group consisting of barium iodide, calcium iodide, tin iodide, and titanium iodide can be included, and among these, potassium iodide is preferable because of its high solubility in water. The iodide content may be 0.01 to 10% by weight with respect to 100% by weight of water, but is not limited, and may preferably be 0.1 to 5% by weight.

In order to increase the iodine complex content in the polarizer-forming film, boric acid may be added to the dyeing tank in an amount of 0.3 to 5% by weight with respect to 100% by weight of water. Not. When boric acid dyeing tank is less than 0.3 wt%, _{PVA-I 3} ^- complex and _{PVA-I 5} ^- it may not be effective in increasing the complex content, boric acid dyeing tank 5 If the concentration is higher than% by weight, the risk of film breakage may increase.

  The temperature of the dyeing tank may be 5 to 42 ° C, but is not limited thereto, and may preferably be 10 to 35 ° C. Moreover, the immersion time of the film for forming a polarizer in the dyeing tank is not particularly limited, and may be 1 to 20 minutes, preferably 2 to 10 minutes.

  In the present invention, the stretching step can be performed together with the dyeing step. At this time, the stretching ratio may be 1.01 to 2.0 times, but is not limited thereto, and preferably 1. It may be 1 to 1.8 times.

  The cumulative stretch ratio up to the dyeing step including the swelling and the dyeing step may be 1.2 to 4.0 times. If the cumulative stretch ratio is less than 1.2 times, wrinkles of the film may occur and appearance defects may occur, and if it exceeds 4.0 times, the initial optical characteristics may be fragile.

<Crosslinking step>
The cross-linking step is a step of fixing the adsorbed iodine molecules by immersing the dyed polarizer forming film in an aqueous solution for cross-linking so that the dyeability by physically adsorbed iodine molecules does not deteriorate due to the external environment. It is.

  When iodine, which is a dichroic dye, has insufficient crosslinking reaction, iodine molecules may be detached by a moist heat environment, and thus sufficient crosslinking reaction is required. Further, in order to orient the iodine molecules located between the molecules of the polarizer-forming film and improve the optical properties, stretching at the largest stretching ratio can be performed in the crosslinking step.

  In the method for producing a polarizer of the present invention, the crosslinking step includes a first crosslinking step and a second crosslinking step, and at least one of the first and second crosslinking steps is for crosslinking containing a boron compound. An aqueous solution can be used. This can improve the optical properties and color durability of the polarizer.

  As the aqueous solution for crosslinking, a known aqueous crosslinking solution can be used without particular limitation. For example, the aqueous solution for crosslinking may contain water as a solvent and a boron compound such as boric acid or sodium borate. It may further contain an organic solvent and iodide that are mutually soluble.

  Boron compounds impart short crosslinks and stiffness to the polarizer, and can suppress wrinkling of the film during the process, improving the handleability of the film and forming the iodine orientation of the polarizer Can play a role.

  The boron compound content may be a content known in the art, and may be, for example, 1 to 10% by weight, preferably 2 to 6% by weight with respect to 100% by weight of water. Good. When the content is less than 1% by weight, the crosslinking effect of the boron compound is reduced, and it may be difficult to impart rigidity to the polarizer. When the content exceeds 10% by weight, the crosslinking reaction of the inorganic crosslinking agent is excessive. When activated, the crosslinking reaction of the organic crosslinking agent may not proceed effectively.

  In this step, iodide can be used to maintain the uniformity of the degree of polarization in the plane of the polarizer and to prevent desorption of the dyed iodine. The iodide may be the same as that used in the dyeing step, and its content may be 0.05 to 15% by weight with respect to 100% by weight of water, but is not limited, preferably May be from 0.5 to 14% by weight. If the content is less than 0.05% by weight, iodine ions in the film may escape and increase the transmittance of the polarizer. If the content exceeds 15% by weight, iodine ions in the aqueous solution may be added to the film. It can penetrate and reduce the transmittance of the polarizer.

  In the present invention, the temperature of the crosslinking tank may be 20 to 70 ° C., but is not limited thereto. The immersion time of the film for forming a polarizer in the crosslinking tank may be 1 second to 15 minutes, but is not limited thereto, and may preferably be 5 seconds to 10 minutes.

  The cross-linking step of the present invention includes first and second cross-linking steps, and the stretching step is performed together.

  The draw ratio of the first crosslinking step may be 2.00 to 3.00 times, preferably 2.20 to 2.80 times. The first crosslinking step according to the present invention improves the mechanical properties of the polarizer by stretching the polarizer-forming film at a high stretch ratio, and prevents the polarizer-forming film from being broken in the subsequent second crosslinking step. To do. If the stretch ratio of the first crosslinking step is less than 2.00 times, the desired degree of orientation does not appear, so that mechanical properties are not ensured, and if it exceeds 3.00 times, the contraction force in the absorption axis direction may increase. .

  The stretching ratio of the second crosslinking step is 1.00 times or less, preferably 0.80 to 1.00 times, more preferably 0.85 to 1.00 times. The second cross-linking step according to the present invention is a step of relieving the stress generated in the first cross-linking step, and is a step of preventing the polarizer forming film from being broken and reducing the contraction force in the absorption axis direction. When the stretch ratio of the second crosslinking step exceeds 1.00 times, the film may be broken, and there is a problem that the shrinkage force in the absorption axis direction increases.

  The cumulative stretching ratio of the first and second crosslinking steps may be 1.5 to 3.0 times, preferably 1.98 to 2.8 times. If the cumulative stretching ratio is less than 1.5 times, the orientation effect of the film for forming a polarizer may be insufficient. If it exceeds 3.0 times, the stress due to stretching increases and the absorption axis increases. Directional contraction force can be increased.

<Complementary color step>
The complementary color step is a step of stabilizing the iodine complex by orienting the iodine complex located between the molecules in the polarizer-forming film on which the iodine complex is physically adsorbed in the vicinity of the boric acid bridge. . Further, through the complementary color step, the color can be corrected for the polarizer-forming film in which the iodine complex is not sufficiently dyed in the crosslinking step.

  The complementary color aqueous solution in the complementary color step contains, for example, water as a solvent and a boron compound such as boric acid, and may further contain an organic solvent and iodide that are mutually soluble with water.

  In the present invention, the boron compound imparts short crosslinks and rigidity to the polarizer, and suppresses wrinkling of the film during the process, thereby improving the handleability of the film and improving the iodine orientation of the polarizer. Can play a role to form.

  The content of the boron compound may be 1 to 10% by weight with respect to 100% by weight of water, but is not limited thereto, and may preferably be 2 to 6% by weight. When the content is less than 1% by weight, the crosslinking effect of the boron compound is reduced, and it may be difficult to impart rigidity to the polarizer. When the content exceeds 10% by weight, the crosslinking reaction of the inorganic crosslinking agent is excessive. When activated, the crosslinking reaction of the organic crosslinking agent may not proceed effectively.

  In this step, iodide can be used to maintain the uniformity of the degree of polarization in the plane of the polarizer and to prevent desorption of the dyed iodine. The iodide may be the same as that used in the dyeing step, and the content may be 0.05 to 15% by weight with respect to 100% by weight of water, but is not limited thereto. Preferably, it may be 0.5 to 11% by weight. If the content is less than 0.05% by weight, iodine ions in the film may escape and increase the transmittance of the polarizer. If the content exceeds 15% by weight, iodine ions in the aqueous solution may be added to the film. It can penetrate and reduce the transmittance of the polarizer.

  In the present invention, the temperature of the complementary color bath may be 20 to 70 ° C. The immersion time of the polarizer-forming film in the complementary color tank may be 1 second to 15 minutes, but is not limited thereto, and may preferably be 5 seconds to 10 minutes.

  The complementary color step according to the present invention is performed together with the stretching step, wherein the stretching ratio of the complementary color step is higher than the stretching ratio of the second crosslinking step and lower than the stretching ratio of the first crosslinking step. The complementary color step according to the present invention maintains a small contraction force in the direction of the absorption axis while realizing a high degree of orientation and improving optical characteristics by stretching a film for forming a polarizer at a relatively high stretch ratio. Can do.

  A more specific example of the stretching ratio in the complementary color step may be 1.01 to 1.25 times, and preferably 1.05 to 1.20 times. The effect of the complementary color step described above can be excellently exhibited within the range of the stretch ratio. If the draw ratio is less than 1.01 times, the stabilization effect of the iodine complex and the orientation degree of the film for forming the polarizer may be lowered. If it exceeds 1.25 times, the film is broken by excessive stretching. May occur, and production efficiency may be reduced.

<Extension step>
In the present invention, the stretching step may be performed simultaneously with the crosslinking step and the complementary color step as described above, may be performed together with other steps, or may be additionally performed as a separate step.

  According to the production method of the present invention, the total cumulative draw ratio of the polarizer is preferably 5.0 times or more, for example, preferably 5.0 to 7.0 times, and 5.3 to 6.0. More preferably, it is double.

  In this specification, “cumulative stretch ratio” means the product of the stretch ratios in each step.

<Washing step>
The polarizer manufacturing method of the present invention is, as necessary, for immersing a film for forming a polarizer that has been crosslinked and stretched in a washing tank filled with an aqueous washing solution, and for forming the polarizer in steps up to the washing step. A water washing step may be further included to remove unwanted residues such as boric acid attached to the film.

  In the present invention, the aqueous washing solution may be an aqueous washing aqueous solution known in the art without particular limitation, and may be, for example, water, to which an iodide may be further added. Not.

  In the present invention, the temperature of the washing tank may be 10 to 60 ° C., but is not limited thereto, and preferably 15 to 40 ° C.

  The washing step can be omitted, and can be performed each time a step before the washing step such as the dyeing step or the crosslinking step is completed. Further, it may be repeated one or more times, and the number of repetitions is not particularly limited.

<Drying step>
In the production method of the present invention, the drying step is a step of drying the washed film for forming a polarizer, and further improves the orientation of dyed iodine molecules by neck-in by drying. This is a step of obtaining a polarizer having excellent optical characteristics. Neck-in means that the width of the film is narrowed.

  As a drying method, a drying method known in the art can be used in combination without limitation, and methods such as natural drying, hot air drying, air drying, heat drying, far-infrared drying, and microwave drying can be used. Recently, microwave drying in which only water in the film is activated and dried is newly used, and usually hot air drying is mainly used.

  The temperature at which the hot air drying is performed is not particularly limited, but is preferably performed at a relatively low temperature in order to prevent deterioration of the polarizer, and may be, for example, 20 to 90 ° C., preferably 85 ° C. or less. Preferably, it may be 80 ° C. or lower.

  The time for performing the hot air drying is not particularly limited and can be, for example, 1 to 10 minutes.

  The polarizer according to the present invention can be provided as a polarizing plate with a polarizer protective film bonded to at least one surface.

  The type of the protective film is not particularly limited as long as it is a film excellent in transparency, mechanical strength, thermal stability, moisture shielding property, isotropy, etc. Specific examples include polyethylene terephthalate, polyethylene Polyester resins such as isophthalate and polybutylene terephthalate; Cellulosic resins such as diacetylcellulose and triacetylcellulose; Polycarbonate resins; Polyacrylic resins such as polymethyl (meth) acrylate and polyethyl (meth) acrylate; Polystyrene and acrylonitrile Styrene resin such as styrene copolymer; Polyolefin resin such as polyethylene, polypropylene, cyclo- or norbornene-structured polyolefin, ethylene-propylene copolymer; Nylon, aromatic polyamide, etc. Polyamide resins; imide resins; polyethersulfone resins; sulfone resins; polyetherketone resins; sulfided polyphenylene resins; vinyl alcohol resins; vinylidene chloride resins; vinyl butyral resins; Examples include a methylene resin; a film made of a thermoplastic resin such as an epoxy resin, and a film made of a blend of the thermoplastic resins can also be used. Also, a film made of a thermosetting resin such as (meth) acrylic, urethane, epoxy, or silicon, or an ultraviolet curable resin can be used. Among these, a film composed of a cellulose resin having a surface saponified with alkali or the like is particularly preferable in view of polarization characteristics or durability. Further, the protective film may have a function of the following optical layer.

  The structure of the polarizing plate is not particularly limited, and various types of optical layers that can satisfy required optical characteristics may be laminated on a polarizer. For example, a structure in which a protective film for protecting a polarizer is laminated on at least one surface of a polarizer; a hard coating layer, an antireflection layer, an anti-adhesion layer, a diffusion prevention layer, an antiglare layer on at least one surface of the polarizer or on the protective film A structure in which a surface treatment layer such as a layer is laminated; a structure in which an alignment liquid crystal layer for compensating a viewing angle or another functional film is laminated on at least one surface of a polarizer or a protective film Good. In addition, a wave plate (including a λ plate) such as an optical film such as a polarization conversion device, a reflector, a semi-transmissive reflector, a half-wave plate or a quarter-wave plate used for forming various image display devices. A structure in which one or more of a phase difference plate, a viewing angle compensation film, and a brightness enhancement film are stacked as an optical layer. More specifically, the polarizing plate has a structure in which a protective film is laminated on one surface of a polarizer, and a reflective polarizing plate or a semi-transmissive polarizing plate in which a reflector or a semi-transmissive reflector is laminated on the laminated protective film. A plate; an elliptical or circular polarizing plate on which a retardation plate is laminated; a wide viewing angle polarizing plate on which a viewing angle compensation layer or a viewing angle compensation film is laminated; or a polarizing plate on which a brightness enhancement film is laminated.

  You may perform joining of a polarizer and a polarizer protective film using an adhesive composition. Bonding of the polarizer and the protective film using the adhesive composition can be performed by an appropriate method, such as casting method, Mayer bar coating method, gravure coating method, die coating method, dip coating method, spraying method, etc. The method of apply | coating an adhesive composition to the adhesive surface of a polarizing film and / or a protective film, and making both overlap is mentioned. The casting method is a method in which an adhesive composition is applied to the surface of an object to be coated while moving a polarizer or a protective film to be coated in a substantially vertical direction, a substantially horizontal direction, or an oblique direction therebetween. .

  After apply | coating an adhesive composition, a polarizer and a protective film are pinched | interposed and joined by a nip roll.

  Moreover, in order to improve adhesiveness, surface treatments such as plasma treatment, corona treatment, ultraviolet irradiation treatment, flame treatment, and saponification treatment can be appropriately performed on the surface of the polarizer and / or protective film. Examples of the saponification treatment include a method of immersing in an aqueous solution of an alkali such as sodium hydroxide or potassium hydroxide.

  A drying process is implemented after laminating | stacking a polarizer and a polarizer protective film. The drying process is performed, for example, by spraying hot air, and the temperature at that time is appropriately selected in the range of 50 to 100 degrees. The drying time is usually 30 to 1,000 seconds.

  The polarizing plate according to the present invention is applicable not only to a normal liquid crystal display device but also to various image display devices such as an organic electroluminescence display device (OLED), a plasma display device, and a field emission display device.

  The following examples are presented to assist in understanding the present invention, but these examples are merely illustrative of the invention and are not intended to limit the scope of the appended claims. It will be apparent to those skilled in the art that various changes and modifications can be made to the embodiments within the scope of the technical idea, and these changes and modifications should be within the scope of the appended claims.

<Example 1>
After a transparent unstretched polyvinyl alcohol film (PE60, KURARAY) having a saponification degree of 99.9% or more was immersed in water (deionized water) at 25 ° C. for 1 minute and 20 seconds to swell (swelling step) Dyeing by immersing in an aqueous dyeing solution at 30 ° C. containing 1.25% by weight of potassium iodide and 0.3% by weight of boric acid for 1.25 mM / L of iodine and 100% by weight of water for 2 minutes and 30 seconds (Staining step). At this time, in the swelling and dyeing steps, the film was stretched at stretch ratios of about 1.7184 times and about 1.5214 times, respectively, and stretched so that the cumulative stretch ratio up to the dyeing tank was 2.614 times. Next, while immersing in an aqueous solution for crosslinking at 56 ° C. containing 13.9% by weight of potassium iodide and 3% by weight of boric acid with respect to 100% by weight of water for 26 seconds to crosslink (first crosslinking step), 2 The film was drawn at a draw ratio of 36 times. Then, while being immersed in a 56 ° C. aqueous solution for crosslinking containing 13.9% by weight of potassium iodide and 3% by weight of boric acid with respect to 100% by weight of water for 20 seconds to crosslink (second crosslinking step), The film was stretched at a stretching ratio of 0.90.
Next, the film was stretched 1.08 times while immersed in a complementary color aqueous solution at 40 ° C. containing 5% by weight of potassium iodide and 2% by weight of boric acid with respect to 100% by weight of water (complementary color step).

  At this time, the total cumulative draw ratio of the swelling, dyeing, crosslinking, and complementary color steps was set to 6 times. After the crosslinking was completed, the polyvinyl alcohol film was washed with deionized water (water washing step) and then dried in an oven at 80 ° C. for 5 minutes (drying step) to produce a polarizer having a transmittance of 42.5%. The thickness of the polarizer was 23 μm.

  A polarizing plate was produced by laminating a triacetyl cellulose (TAC) film on both surfaces of the produced polarizer.

<Examples 2 to 10 and Comparative Examples 1 to 6>
As described in Table 1 below, a polarizing plate was produced in the same manner as in Example 1 except that the stretching ratio was adjusted.

<Test example>
The physical properties of the polarizers produced in the above Examples and Comparative Examples were measured by the following methods, and the results are shown in Table 2 below.

<1. Optical properties (degree of polarization)>
After the manufactured polarizer was cut into a size of 4 cm × 4 cm, the transmittance was measured using an ultraviolet-visible light spectrometer (V-7100, manufactured by JASCO). At this time, the degree of polarization is defined by Equation 2 below.
[Formula 2]
Polarization degree (P) = [(T ₁ −T ₂ ) / (T ₁ + T ₂ )] ^1/2
(In the formula, T ₁ is a parallel transmittance obtained when a pair of polarizers are arranged in a state where the absorption axes are parallel, and T ₂ is a case where a pair of polarizers is arranged in a state where the absorption axes are orthogonal to each other. It is the orthogonal transmittance obtained).

<2. Orientation degree>
After the produced polarizer is cut into a size of 4 cm × 4 cm, the IR beam is polarized using a polarization ATR apparatus (VeeMAX III, PIKE, incident angle: 45 °), and the polarized IR beam and the polarizer sample Absorbance is measured by FT-IR so that the MD direction (absorption axis direction) is parallel (A _MD ) (Nicolet Continuum XL, Thermo). Next, the absorbance is measured by FT-IR so that the polarized IR beam is parallel to the TD direction (transmission axis direction) of the polarizer sample (A _TD ).
The absorbance at 1290 cm ⁻¹ indicating the difference in absorbance in the MD and TD directions was measured.
The measured absorbance was substituted into Equation 1 to obtain the degree of orientation.

<3. Contraction force>
Here, the contraction force in the absorption axis direction per 2 mm width in the transmission axis direction of the polarizer was measured. The polarizers produced in the examples and comparative examples were cut to a size of 3.0 cm (absorption axis direction) × 2 mm (transmission axis direction), and then DMA Q800 (Dynamic mechanical analyzer, TA) at 80 ° C. for 4 hours. The shrinkage force in the absorption axis direction was measured at the time of standing. At this time, in order to maintain the polarizer in a flat state before the measurement, the minimum load was applied in the thickness direction of the polarizer.

  Referring to Table 2, it can be confirmed that the polarizer of the present invention satisfies both the high degree of orientation and the small contraction force in the absorption axis direction and is excellent in the degree of polarization.

  However, in the case of the comparative example, it is understood that when the degree of polarization is excellent, the contraction force in the absorption axis direction is high, and when the contraction force in the absorption axis direction is low, the degree of polarization is low.

Claims (7)

The degree of orientation is 0.250 to 0.400, the contraction force in the absorption axis direction is 3.5 N / 2 mm or less,
The degree of orientation is a polarizer obtained from Equation 1 below:

(Wherein, A _MD is the absorbance of infrared light polarized in the absorption axis direction of the polarizer, A _TD is the absorbance of infrared light polarized in the transmission axis direction of the polarizer, A _large is the A _MD the absorbance of the higher one of _{a TD,} a _small the absorbance of the lower of _{a MD} and _{a TD).}   The polarizer according to claim 1, wherein the degree of orientation is 0.300 to 0.400. Including swelling, dyeing, stretching, cross-linking, complementary color and drying steps of the polarizer-forming film,
The cross-linking step includes a first cross-linking step of stretching the polarizer forming film to 2.00 to 3.00 times, and a first forming step of stretching the polarizer forming film to 1.00 times or less after the first cross-linking step. 2 cross-linking steps,
In the complementary color step, the polarizer forming film is stretched at a stretch ratio that is higher than the stretch ratio of the second cross-linking step and lower than the stretch ratio of the first cross-linking step.   The method for producing a polarizer according to claim 3, wherein in the second crosslinking step, the polarizer-forming film is stretched 0.85 to 1.00 times.   The method for producing a polarizer according to claim 3 or 4, wherein in the complementary color step, the film for forming a polarizer is stretched by 1.01 to 1.25 times.   A polarizing plate comprising the polarizer according to claim 1 and 2 and a polarizer protective film bonded to at least one surface of the polarizer.   An image display device comprising the polarizing plate according to claim 6.