KR20170089439A - Polarizer and method for manufacturing same - Google Patents

Abstract

(식 중, A_MD는 편광자의 흡수축 방향으로 편광하는 적외광의 흡광도이고, A_TD는 편광자의 투과축 방향으로 편광하는 적외광의 흡광도이며, A_large는 A_MD와 A_TD 중 높은 쪽의 흡광도이고, A_small은 A_MD와 A_TD 중 낮은 쪽의 흡광도이다).A degree of orientation of 0.250 to 0.400 and a shrinking force in the direction of the absorption axis of 3.5 N / 2 mm or less, and the degree of orientation is a polarizer obtained from the following formula:

A _MD is the absorbance of the infrared light polarized in the absorption axis direction of the polarizer, A _TD is the absorbance of the infrared light polarized in the direction of the transmission axis of the polarizer, A _large is the difference between A _MD and A _TD , A _small is the lower absorbance of A _MD and A _TD ).

Description

[0001] POLARIZER AND METHOD FOR MANUFACTURING SAME [0002]

The present invention relates to a polarizer and a manufacturing method thereof, and more particularly, to a polarizer having excellent optical characteristics and small shrinking force in an absorption axis (stretching) direction and a manufacturing method thereof.

BACKGROUND ART Polarizing plates used in various image display devices such as liquid crystal display (LCD), electroluminescence (EL) display, plasma display (PDP), field emission display (FED) and OLED are generally made of polyvinyl alcohol alcohol, PVA) film comprises a polarizer in which an iodine compound or a dichroic polarizing material is adsorbed and oriented, a polarizer protective film is laminated on one side of the polarizer, a polarizer protective film is provided on the other side of the polarizer, And a releasing film laminated in this order.

The polarizer constituting the polarizing plate is applied to an image display apparatus, and it is basically required to have a high transmittance and a high polarization degree in order to provide an image with excellent color reproducibility. In order to realize this, a polarizer was prepared by modifying the polyvinyl alcohol film itself or using a method of using an immiscible dichroic dye instead of a sublimable iodine polarizing element.

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

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

However, polarizers that have realized high polarization and low shrinkage power are not known.

Japanese Patent Application Laid-Open No. 2010-145866 discloses a method for producing a polarizer having a small shrinkage stress, but fails to provide a satisfactory alternative to the above-mentioned problem.

Japanese Patent Laid-Open No. 2010-145866

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

1. A liquid crystal display comprising: an orientation degree of 0.250 to 0.400 and a contractive force in the direction of an absorption axis of 3.5 N /

The degree of orientation is determined by a polarizer obtained from the following formula:

A _MD is the absorbance of the infrared light polarized in the absorption axis direction of the polarizer, A _TD is the absorbance of the infrared light polarized in the direction of the transmission axis of the polarizer, A _large is the difference between A _MD and A _TD , A _small is the lower absorbance of A _MD and A _TD ).

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

3. A polarizer-forming film comprising swelling, dyeing, stretching, crosslinking, complementing and drying steps,

Wherein the crosslinking step includes a first crosslinking step of stretching the polarizer forming film to 2.00 to 3.00 times and a second crosslinking step of stretching the polarizer forming film to 1.00 times or less after the first crosslinking step,

Wherein the film for polarizer formation is stretched at a stretching ratio higher than the stretching ratio of the second crosslinking step and lower than the stretching ratio of the first crosslinking step in the complementary coloring step.

4. The method of producing a polarizer as described in 3 above, wherein the polarizing film is stretched at 0.85 to 1.00 times in the second crosslinking step.

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

6. A polarizer comprising the polarizer described in 1 or 2 above and a polarizer protective film bonded to at least one side of the polarizer.

7. An image display device comprising the polarizing plate according to 6. above.

 The polarizer of the present invention has a degree of orientation and a shrinking force in the direction of the absorption axis, so that it can exhibit a small shrinking force in the absorption axis direction while having excellent optical properties without deteriorating other physical properties.

The polarizer of the present invention can produce the polarizer according to the present invention by stretching the polarizer-forming film at a stretching ratio within a specific range in the crosslinking step and the complementary coloring step. Normally, the higher the degree of orientation, the higher the degree of orientation. Thus, in order to realize excellent polarization characteristics, it is necessary to increase the stretching ratio, while the higher the stretching ratio, the greater the shrinking force in the stretching (absorption axis) direction. Therefore, the implementation of a high degree of orientation and a low shrinkage force in the absorption axis direction are in a trade-off relationship, and a polarizer which has heretofore realized high degree of orientation and low shrinkage in the absorption axis direction is not known, The polarizer of the present invention can control the range of the degree of orientation while having a low shrinking force in the direction of the absorption axis and as a result can produce a polarizer having a small shrinking force in the absorption axis direction while having a high degree of polarization.

The present invention relates to a polarizer having a degree of orientation of 0.250 to 0.400 and a shrinking force in the direction of the absorption axis of 3.5 N / 2 mm or less, thereby exhibiting excellent optical characteristics and small shrinking force in the absorption axis direction.

Hereinafter, the present invention will be described in detail.

As described above, conventionally, it is known that the high degree of orientation of the polarizer and the small retraction force in the absorption axis direction are in a trade-off relationship, and an example of realizing a polarizer having an excellent degree of orientation and a small retraction force in the absorption axis direction is not known.

However, the inventors of the present invention have produced a polarizer that simultaneously satisfies both the high degree of orientation and the small shrinkage force in the direction of the absorption axis, through the method of producing a polarizer capable of adjusting the degree of orientation. When the degree of orientation and the contractive force in the absorption axis direction are adjusted to a specific range, a polarizer having a small contractive force in the absorption axis direction can be obtained without lowering 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. When the degree of orientation is less than 0.250, the degree of polarization decreases. When the degree of orientation is more than 0.400, the contraction force in the direction of the absorption axis is increased and the deflection of the polarizer is increased.

In the present invention, the degree of orientation can be adjusted to the above-mentioned range by controlling the stretching ratio in the first crosslinking step to 2.00 to 3.00 times and the total cumulative stretching ratio to 5.0 times or more.

The degree of orientation according to the present invention can be obtained from 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. The specific relational expression for obtaining the specific orientation degree is shown in Equation 1 below.

A _MD is the absorbance of the infrared light polarized in the absorption axis direction (MD direction) of the polarizer, A _TD is the absorbance of the infrared light polarized in the transmission axis direction (TD direction) of the polarizer, A _large is A _MD and A _TD , and A _small is the lower absorbance of A _MD and A _TD ).

The absorbance of infrared light can be measured, for example, by a Fourier transform infrared spectrophotometer (FT-IR). The wave number of the infrared light can be, for example, 1290 cm ^-1 .

The polarizer of the present invention has a low shrinking force in the absorption axis direction and a shrinking force in the absorption axis direction may be 3.5 N / 2 mm or less. When the shrinking force in the direction of the absorption axis is 3.5 N / 2 mm or less, deformation of the polarizer can be effectively prevented. The lower limit of the shrinkage force in the absorption axis direction is more preferable, and the lower limit is not particularly limited, and may be 2N / 2mm or more, 1N / 2mm or more, or 0.1N / 2mm or more. In the present invention, the shrinking force of the polarizer in the absorption axis direction can be adjusted by controlling the stretching ratio of the first crosslinking step to 2.00 to 3.00 times and the stretching ratio of the second crosslinking step to 1.00 times or less.

The thickness of the polarizer of the present invention may be 5 to 30 탆, preferably 10 to 28 탆, and more preferably 15 to 26 탆. When the thickness of the polarizer is within the above range, the low shrinking force in the absorption axis direction of the polarizer and the handling property can be both satisfied.

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

The method for producing a polarizer according to the present invention includes swelling, dyeing, stretching, crosslinking, complementary coloring and drying of a film for forming a polarizer, wherein the crosslinking step comprises a first crosslinking step of stretching the polarizing film to a stretching ratio of 2.00 to 3.00, And a second crosslinking step of stretching the film for forming a polarizer after the first crosslinking step to 1.00 times or less to relax the stress, wherein in the complementary coloring step, the stretching ratio of the second crosslinking step is higher than the stretching ratio of the first crosslinking step The film for forming a polarizer is stretched at a low stretching ratio. By adjusting the degree of orientation of the polarizer and the shrinkage force in the absorption axis direction by controlling the stretching ratio of the crosslinking step and the complementary coloring step as described above, a high degree of polarization and a shrinking force in a small absorption axis direction can be realized.

The method for producing the polarizer of the present invention will be described in more detail as follows.

The polarizer-forming film for producing the polarizer may be a polymer film used for producing a polarizing plate, and a film which can be dyed by a dichroic substance (for example, iodine) known in the art may be used without any particular limitation. A polyvinyl alcohol film, a partially saponified polyvinyl alcohol film; A hydrophilic polymer film such as a polyethylene terephthalate film, an ethylene-vinyl acetate copolymer film, an ethylene-vinyl alcohol copolymer film, a cellulose film, a partially saponified film thereof and the like; A polyvinyl alcohol film, a dehydrated polyvinyl alcohol film, a dehydrochloric acid-treated polyvinyl chloride film, and the like; Etc. may be used. Of these, a polyvinyl alcohol-based film is preferable because it not only exerts an effect of enhancing the uniformity of the degree of polarization in the plane but also is excellent in dye 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 coloring step, a stretching step, a washing step and a drying step, and may be classified by a stretching method. For example, a dry stretching method, a wet stretching method, or a hybrid stretching method in which the two kinds of stretching methods are mixed can be used. Hereinafter, a method of producing the polarizer of the present invention will be described by way of a wet drawing method, but the present invention is not limited thereto.

The steps other than the drying step may be performed in a state in which the film for forming a polarizer is immersed in a constant temperature bath filled with one or more kinds of solutions selected from various kinds of solutions.

<Swelling step>

The swelling step is carried out by immersing the unstretched polarizer forming film in a swelling tank filled with an aqueous swelling solution before dyeing to remove impurities such as dust or anti-blocking agent deposited on the surface of the polarizer forming film and to swell the polarizing film To improve the stretching efficiency and prevent uneven dyeing, thereby improving the physical properties of the polarizer.

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

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

The execution time of the swelling step (swelling tank immersion time) can be applied without particular limitation to the known execution time, for example, 180 seconds or less, preferably 90 seconds or less. When the immersion time is within the above range, excessive swelling and saturation can be suppressed, breakage due to softening of the polarizer-forming film can be prevented, adsorption of iodine can be uniformed in the dyeing step, and polarization degree can be improved .

The stretching step may be performed together with the swelling step, and the stretching ratio may be about 1.1 to 3.5 times, but is not limited to, preferably 1.5 to 3.0 times. If the stretching ratio is less than 1.1 times, wrinkling may occur. If the stretching ratio is more than 3.5 times, initial optical characteristics may be weakened.

<Stage of dyeing>

The dyeing step is a step of immersing the polarizing film in a dyeing bath filled with a dyeing aqueous solution containing a dichroic substance, for example, iodine, to adsorb iodine on the polarizing film.

The aqueous solution for dyeing may be an aqueous solution for dyeing well known in the art without any particular limitation, and may include water, a water-soluble organic solvent or a mixed solvent thereof and iodine. The content of iodine may be 0.4 to 400 mmol / L in the dyeing aqueous solution, but is not limited thereto, preferably 0.8 to 275 mmol / L, and most preferably 1 to 200 mmol / L.

The dyeing aqueous solution may further contain iodide as a dissolution aid so that the dyeing efficiency can be improved. As iodide, iodide known in the art can be used without limitation, and examples thereof include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, calcium iodide, tin iodide , And titanium iodide. Of these, potassium iodide is preferable in view of high solubility in water. The content of iodide may be 0.01 to 10% by weight, but is not limited to 0.1 to 5% by weight based on 100% by weight of water.

In addition, in order to increase the content of the iodine complex in the polarizer-forming film, boric acid may be added to the dyeing tank in an amount of 0.3 to 5% by weight based on 100% by weight of water, but is not limited thereto. If boric acid in the dyeing tank is less than 0.3% by weight, the PVA-I ₃ -complex and the PVA-I ₅ -content content may not be increased. If the dyeing tank boric acid concentration is higher than 5% by weight, The risk can be increased.

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

In the present invention, the stretching step may be performed together with the dyeing step. In this case, the stretching ratio may be 1.01 to 2.0 times, but not limited thereto, preferably 1.1 to 1.8 times.

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

<Bridging stage>

In the crosslinking step, the dyed film for forming a polarizer is immersed in an aqueous crosslinking solution to immobilize the adsorbed iodine molecules so that the dyeability due to physically adsorbed iodine molecules is not lowered by the external environment.

If iodine, which is a dichroic dye, is insufficient in cross-linking reaction, iodine molecules may be desorbed by a moist heat environment, and sufficient crosslinking reaction is required. Further, in order to orient the iodine molecules positioned between the molecules of the polarizer-forming film and improve the optical properties, stretching at the greatest stretching ratio can be carried out in the crosslinking step.

The method for producing a polarizer according to the present invention is characterized in that the crosslinking step includes a first crosslinking step and a second crosslinking step and at least one of the first and second crosslinking steps may use a crosslinking aqueous solution containing a boron compound. Whereby the optical characteristics and color durability of the polarizer can be improved.

As the aqueous solution for crosslinking, a crosslinked aqueous solution known in the art can be used without any particular limitation. For example, water as a solvent and a boron compound such as boric acid or sodium borate, an organic solvent mutually soluble with water, Iodide may be further included.

The boron compound imparts short crosslinking and rigidity to the polarizer to suppress the occurrence of wrinkles in the film during the process, thereby improving the handleability of the film and forming the iodine orientation of the polarizer.

The content of the boron compound may be a known amount in the art, for example, 1 to 10% by weight, preferably 2 to 6% by weight based on 100% by weight of water. If the content is less than 1% by weight, the crosslinking effect of the boron compound may decrease, 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 excessively activated, It may be difficult to proceed effectively.

In this step, iodide can be used to maintain the uniformity of polarization within 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, more preferably 0.5 to 14% by weight, based on 100% by weight of water. If the content is less than 0.05% by weight, the iodide ion in the film may escape to increase the transmittance of the polarizer. If the content exceeds 15% by weight, iodide ions in the aqueous solution may penetrate into the film and transmittance of the polarizer may be decreased .

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

The crosslinking step of the present invention comprises a first and a second crosslinking step, and the stretching step is carried out together.

The stretching 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 enhances the mechanical properties of the polarizer by stretching the polarizer-forming film at a high stretching ratio, and prevents the polarizer-forming film from being broken in the subsequent second crosslinking step. If the stretching ratio of the first crosslinking step is less than 2.00 times, the desired degree of orientation is not exhibited, and mechanical properties are not secured. If the stretching ratio exceeds 3.00 times, the contracting force in the absorption axis direction may increase.

The stretching ratio of the second crosslinking step may be 1.00 times or less, preferably 0.80 to 1.00 times, and more preferably 0.85 to 1.00 times. The second crosslinking step according to the present invention is a step of relaxing the stress generated in the first crosslinking step and preventing the polarizer forming film from breaking and lowering the contracting force in the absorption axis direction. If the stretching ratio of the second crosslinking step exceeds 1.00 times, film breakage may occur and the shrinking 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, there is a possibility that the orientation effect of the polarizing film is insufficient. If the cumulative stretching ratio is more than 3.0 times, the stress due to stretching increases and the contraction force in the absorption axis direction may increase.

<Complementary phase>

The complementary step is a step of stabilizing the iodine complex by orienting the iodine complex positioned between the molecule and the molecule near the boric acid bridge in a polarizer forming film in which the iodine complex is physically adsorbed. Further, through the complementary color step, the color can be corrected for the polarizer forming film in which the dyeing of the iodine complex in the crosslinking step is insufficient.

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

In the present invention, the boron compound imparts short crosslinking and rigidity to the polarizer to suppress the occurrence of wrinkles in the film during the process, thereby improving the handleability of the film and forming the iodine orientation of the polarizer.

The content of the boron compound may be 1 to 10% by weight based on 100% by weight of water, but is not limited thereto and preferably 2 to 6% by weight. If the content is less than 1% by weight, the crosslinking effect of the boron compound may decrease, 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 excessively activated, It may be difficult to 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 also 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 based on 100% by weight of water, but is not limited thereto, and may be preferably 0.5 to 11% by weight. If the content is less than 0.05% by weight, iodide ions in the film may escape to increase the transmittance of the polarizer. If the content exceeds 15% by weight, iodide ions in the aqueous solution may penetrate into the film and transmittance of the polarizer may be decreased.

In the present invention, the temperature of the complementary color bath may be 20 to 70 占 폚. The immersion time of the film for forming a polarizer in the sub-color tones may be from 1 second to 15 minutes, but is not limited thereto, and preferably from 5 seconds to 10 minutes.

The complementary coloring step according to the present invention is performed together with the stretching step, wherein the stretching ratio of the complementary coloring step is higher than the stretching ratio of the second crosslinking step and lower than the stretching ratio of the first crosslinking step. In the complementary step according to the present invention, by stretching the film for forming a polarizer at a relatively high stretching ratio, a high degree of orientation can be realized, and a small contracting force in the absorption axis direction can be maintained while improving optical characteristics.

More specific examples of the stretching ratio of the complementary color step may be 1.01 to 1.25 times, preferably 1.05 to 1.20 times. The effect of the complementary color step described above can be excellently exhibited in the range of the stretching ratio. If the stretching ratio is less than 1.01 times, there is a possibility that the stabilizing effect of the iodine complex and the degree of orientation of the polarizing film are lowered. If the stretching ratio is more than 1.25 times, the film may be broken due to excessive stretching and the production efficiency may be lowered.

<Stretching step>

In the present invention, the stretching step may be performed simultaneously with the crosslinking step and the complementary coloring step as described above, may be performed together with other steps, or may be performed separately as a separate step.

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

In the present specification, the term "cumulative stretching ratio" means the product of the stretching ratio at each step.

<Washing step>

The polarizer-producing method of the present invention is a method for producing a polarizer, which comprises immersing a film for forming a polarizer in which crosslinking and stretching have been completed in a water bath filled with an aqueous solution for washing, And may further include a water washing step of removing unnecessary residues.

In the present invention, an aqueous solution for washing with water may be used without any particular limitation, and may be water or iodide, for example, but not limited thereto.

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

The washing step may be omitted, and may be performed each time the washing step before the washing step such as the dyeing step or the crosslinking step is completed. It may also be repeated one or more times, and the number of repetition is not particularly limited.

<Drying step>

In the manufacturing method of the present invention, the drying step is a step of drying the washed polarizer-forming film, which further improves the orientation of the molecules of the iodine dissolved in the neck-in to thereby produce a polarizer excellent in optical characteristics . On the other hand, the neckline means that the width of the film is narrowed.

As the drying method, a drying method known in the art can be used in combination without limitation, and for example, natural drying, hot air drying, air drying, heat drying, far infrared ray drying and microwave drying can be used. Is used to dry only the water in the microwave, and usually, hot air drying is mainly used.

The temperature for carrying out the hot air drying is not particularly limited, but it is preferably carried out at a relatively low temperature in order to prevent deterioration of the polarizer. For example, it may be 20 to 90 ° C, preferably 85 ° C or less, Or less.

The duration of the hot air drying is not particularly limited, and may be, for example, 1 to 10 minutes.

The polarizer according to the present invention may be provided as a polarizer by bonding a polarizer protective film to at least one side thereof.

The kind 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 thereof include polyesters such as polyethylene terephthalate, polyethylene isophthalate and polybutylene terephthalate Based resin; Cellulose-based resins such as diacetylcellulose and triacetylcellulose; Polycarbonate resin; Polyacrylic resins such as polymethyl (meth) acrylate and polyethyl (meth) acrylate; Styrene resins such as polystyrene and acrylonitrile-styrene copolymer; Polyolefin resins such as polyethylene, polypropylene, cycloolefins, or polyolefins having a norbornene structure, and ethylene propylene copolymers; Polyamide resins such as nylon and aromatic polyamide; Imide resin; Polyether sulfone type resin; sulfone type resin; Polyether ketone resin; A sulfided polyphenylene resin; Vinyl alcohol-based resin; Vinylidene chloride resins; Vinyl butyral resin; Allylate series resin; Polyoxymethylene type resin; Epoxy resin, and the like, and a film composed of the blend of the thermoplastic resin may also be used. Further, a film made of a thermosetting resin such as (meth) acrylic, urethane, epoxy, or silicone or a film made of an ultraviolet curable resin may also be used. Among them, a film made of a cellulose-based resin having a surface that is particularly sensitized with an alkali or the like is preferable in consideration of polarization characteristics or durability. Further, the protective film may have the function of the optical layer described below.

The structure of the polarizing plate is not particularly limited, and various types of optical layers capable of satisfying required optical characteristics may be laminated on the 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 structure in which a surface treatment layer such as a hard coating layer, an antireflection layer, an adhesion preventive layer, a diffusion preventing layer, an antiglare layer, or the like is laminated on at least one surface of a polarizer or on a protective film; It may have a structure in which an alignment liquid crystal layer or another functional film is laminated on at least one surface of the polarizer or on the protective film to compensate for the viewing angle. A retardation plate including a wave plate (including? Plate) such as an optical film such as a polarization conversion device used for forming various image display devices, a reflector, a transflective reflector, a half-wave plate or a quarter- A viewing angle compensation film, and a brightness enhancement film may be stacked as an optical layer. More specifically, the present invention relates to a polarizing plate having a structure in which a protective film is laminated on one surface of a polarizer, which comprises a reflective polarizing plate or a transflective polarizing plate in which a reflector or a transflective reflector is laminated on a laminated protective film; An elliptic or circular polarizer in which a retarder is stacked; A wide viewing angle polarizer in which a viewing angle compensating layer or a viewing angle compensating film is laminated; Or a polarizing plate in which a brightness enhancement film is laminated.

The bonding of the polarizer and the polarizer protective film may be performed using an adhesive composition. The bonding of the polarizer and the protective film using the adhesive composition can be carried out by an appropriate method. For example, the polarizing film and / or the protective film may be bonded by a flexible method, a Meyer bar coating method, a gravure coating method, a die coating method, an immersion coating method, A method in which an adhesive composition is applied to the adhesive surface of the film, and both are overlapped. The flexible method is a method of applying an adhesive composition to a surface of a polarizer or protective film as a coating material while moving the polarizer or protective film in a substantially vertical direction, a substantially horizontal direction, or an oblique direction between them.

After the adhesive composition is applied, the polarizer and the protective film are sandwiched by a nip roll.

In order to improve the adhesion, the surface of the polarizer and / or the protective film may be appropriately subjected to surface treatment such as plasma treatment, corona treatment, ultraviolet ray irradiation treatment, frame treatment, and saponification treatment. The saponification treatment includes a method of immersing in an aqueous alkali solution such as sodium hydroxide or potassium hydroxide.

After the polarizer and the polarizer protective film are laminated, a drying treatment is performed. The drying treatment is carried out, for example, by spraying hot air, and the temperature at that time is suitably 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 to various image display devices such as an organic light emitting display (OLED), a plasma display, and a field emission display as well as a general liquid crystal display.

It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to be illustrative of the present invention and are not intended to limit the scope of the appended claims. It will be apparent to those skilled in the art that such variations and modifications are within the scope of the appended claims.

&Lt; Example 1 >

(Swelling step) was immersed in water (deionized water) at 25 DEG C for 1 minute and 20 seconds and then swelled (swelling step), and then immersed in a solution of 1.25 mM iodine / (Dyeing step) by immersing in an aqueous solution for dyeing at 30 DEG C for 2 minutes and 30 seconds containing 1.25 wt% of potassium iodide and 0.3 wt% of boric acid per 100 wt% of the aqueous solution. At this time, stretching was performed at a stretching ratio of about 1.7184 times and about 1.5214 times at the swelling and dyeing stages, respectively, and the stretching ratio was increased to 2.614 times to the dyeing bath. Subsequently, the resultant was immersed in a crosslinking aqueous solution at 56 ° C containing 13.9% by weight of potassium iodide and 3% by weight of boric acid per 100% by weight of water for 26 seconds to effect crosslinking (first crosslinking step) and stretching at a stretching ratio of 2.36 times. Thereafter, the film was immersed in a crosslinking aqueous solution at 56 ° C containing 13.9% by weight of potassium iodide and 3% by weight of boric acid per 100% by weight of water for 20 seconds to be crosslinked (second crosslinking step) and stretched at a stretching ratio of 0.90.

Subsequently, the coated film was stretched 1.08 times by immersing it in a complementary-color aqueous solution containing 40 wt% of potassium iodide and 2 wt% of boric acid for 10 seconds (complementary step) to 100 wt% of water.

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

A triacetylcellulose (TAC) film was laminated on both sides of the prepared polarizer to prepare a polarizing plate.

&Lt; Examples 2 to 10 and Comparative Examples 1 to 6 >

A polarizing plate was prepared in the same manner as in Example 1 except that the stretching ratio was adjusted as shown in Table 1 below.

<Test Example>

The physical properties of the polarizers prepared 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 (polarization degree)>

The prepared polarizer was cut into a size of 4 cm x 4 cm, and then the transmittance was measured using an ultraviolet ray spectrophotometer (V-7100, manufactured by JASCO). The polarization degree is defined by the following equation (2).

[Equation 2]

Degree of polarization _{(P) = [(T 1} -T 2) / (T 1 + T 2)] 1/2

(Wherein T ₁ is a parallel transmittance obtained when the pair of polarizers are arranged in parallel with the absorption axis, and T ₂ is a cross transmittance obtained when the pair of polarizers are arranged in a state in which the absorption axes are perpendicular to each other to be).

<2. Orientation degree>

The prepared polarizer was cut into a size of 4 cm x 4 cm and then the IR beam was polarized using a polarized ATR apparatus (VeeMAX III, PIKE, angle of incidence: 45 °), and the polarized IR beam and the MD direction of the polarizer sample Absorbance is measured with FT-IR (A _MD ) (Nicolet Continuum XL, Thermo Inc.) so that it is parallel. Next, the absorbance is measured by FT-IR (A _TD ) so that the polarized IR beam is parallel to the TD direction (transmission axis direction) of the polarizer sample.

The absorbance at 1290 cm &lt; ^-1 &gt; indicating the difference in absorbance in the MD and TD directions was measured.

The measured absorbance was substituted into the above equation 1 to obtain the degree of orientation.

<3. Contractility>

 Here, the retraction force in the absorption axis direction per 2 mm width in the transmission axis direction of the polarizer was measured. The polarizers prepared in Examples and Comparative Examples were cut into a size of 3.0 cm (absorption axis direction) × 2 mm (transmission axis direction) and then left to stand at 80 ° C. for 4 hours by DMA Q800 (Dynamic mechanical analyzer, And the shrinkage force in the absorption axis direction was measured. At this time, a minimum load was measured across the thickness direction of the polarizer to keep the polarizer flat before measurement.

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

However, in the case of the comparative example, it can be seen that when the polarization degree is excellent, the shrinking force in the absorption axis direction is high, and when the shrinking force in the absorption axis direction is low, the polarization degree is low.

Claims (7)

The degree of orientation is 0.250 to 0.400, the contracting force in the direction of the absorption axis is 3.5 N / 2 mm or less,
The degree of orientation is determined by a polarizer obtained from the following formula:

A _MD is the absorbance of the infrared light polarized in the absorption axis direction of the polarizer, A _TD is the absorbance of the infrared light polarized in the direction of the transmission axis of the polarizer, A _large is the difference between A _MD and A _TD , A _small is the lower absorbance of A _MD and A _TD ). The method according to claim 1,
And a degree of orientation of 0.300 to 0.400. Comprising swelling, dyeing, stretching, crosslinking, complementing and drying of the film for forming a polarizer,
Wherein the crosslinking step includes a first crosslinking step of stretching the polarizer forming film to 2.00 to 3.00 times and a second crosslinking step of stretching the polarizer forming film to 1.00 times or less after the first crosslinking step,
Wherein the polarizing film is stretched at a stretching ratio higher than the stretching ratio of the second crosslinking step and lower than the stretching ratio of the first crosslinking step in the complementary coloring step. The method of claim 3,
And the polarizer-forming film is stretched to 0.85 to 1.00 times in the second crosslinking step. The method according to claim 3 or 4,
And the polarizer-forming film is stretched 1.01 to 1.25 times in the complementary coloring step. A polarizer comprising the polarizer according to claim 1 or 2 and a polarizer protective film bonded to at least one side of the polarizer. An image display device comprising the polarizing plate according to claim 6.