TW201617647A - Method for producing polarizer - Google Patents

Abstract

The present invention relates to a method for producing a polarizer, more specifically, the method for producing a polarizer of this invention contains the steps of swelling, dyeing, crosslinking and elongating of a film for polarizer formation. The swelling step, the dyeing step and the crosslinking step are conducted in this order. At least a part of the elongating step is conducted in the dyeing step and/or prior to the dyeing step. After the dyeing step is finished, the distance between the crystals in the film for polarizer formation on the elongating direction is 20 to 40 nm. The dyeing solution contains a boric acid compound.

Description

Method for manufacturing polarizer

The present invention relates to a method of producing a polarizer.

Polarized light used in various image display devices such as liquid crystal display (LCD), electric field (EL) display, plasma display (PDP), electric field emission display (FED), and organic light-emitting diode (OLED) The plate is generally included in a polyvinyl alcohol (PVA) film which is adsorbed and polarized with an iodine compound or a dichroic polarizing material, and has a polarizer protective film laminated on one side of the polarizer. The other side of the polarizer is a multilayered structure in which a polarizer protective film, an adhesive layer bonded to a liquid crystal cell, and a release film are sequentially laminated.

The polarizer constituting the polarizing plate is required to have a high transmittance and a degree of polarization in order to provide an image excellent in reproducibility of color for use in an image display device. In addition, the application of the flat panel display device in various fields has been widely changed, and the tendency to increase in size has become more remarkable, resulting in the use of various image display devices such as liquid crystal display devices for a long period of time in a high temperature state, and the improvement of polarization performance and optical performance. As well as the requirement for improvement in durability, the conditions for the performance of the polarizing plate become very severe. Not only that, but it is also required to have characteristics suitable for various environments and uses. The image display device requires optical durability including hue change under high temperature and high humidity conditions, and high contrast through high alignment/high penetration.

Korean Patent No. 1296786 discloses a method for producing a polarizer, but when the transmittance is high, the problem of lowering the degree of polarization cannot be improved.

[Previous Technical Literature]

[Patent Literature]

[Patent Document 1] Korean Patent No. 1296786

It is an object of the present invention to provide a method for producing a polarizer that enhances optical characteristics and durability.

A method for producing a polarizer, comprising the steps of swelling, dyeing, crosslinking, and stretching of a film for forming a polarizer; wherein the swelling step, the dyeing step, and the crosslinking step are performed in this order; At least a part of the step is performed in the dyeing step and/or before the dyeing step; when the dyeing step is terminated, the distance between the crystal and the crystal in the film for forming the polarizer in the extending direction is 20 to 40 nm; The dyeing liquid contains a boric acid compound.

2. The method of producing a polarizer according to the above 1, wherein the extending direction is an MD direction.

3. The method for producing a polarizer according to the above 1, wherein the boric acid compound is contained in the dyeing liquid in an amount of 0.3 to 5% by weight based on the total weight of the dyeing liquid.

4. The method of producing a polarizer according to the above 1, wherein the cumulative elongation ratio up to the end of the dyeing step is 2.0 to 3.0 times.

5. The method of producing a polarizer according to the above 1, wherein the crosslinking step comprises at least a first crosslinking step and a second crosslinking step.

6. The method for producing a polarizer according to the above 1, wherein the concentration of the boric acid compound in the dyeing liquid in the dyeing step is lower than the concentration of the boric acid compound in the crosslinking liquid in the crosslinking step.

7. The method of producing a polarizer according to the above 1, further comprising a complementary color step.

A polarizer which is produced by the method according to any one of the above 1 to 7.

9. The polarizer of the above 8, wherein the boric acid crosslinking efficiency is from 4.5 to 9.0.

A polarizing plate comprising the polarizer of the above-mentioned 8 and a protective film laminated on at least one surface of the polarizer.

An image display device comprising the polarizing plate of 10 described above.

The method of the present invention can produce a polarizer having high transmittance and improved polarization and excellent optical characteristics.

The method of the present invention is capable of producing a polarizer which significantly improves durability.

Moreover, the method of the present invention also minimizes hue changes when exposed to high temperature conditions for extended periods of time.

The present invention relates to a method for producing a polarizer comprising the steps of swelling, dyeing, crosslinking and stretching of a film for forming a polarizer; the swelling step, the dyeing step, and the crosslinking step are carried out in this order; At least one of the steps is performed at the time of the dyeing step and/or before the dyeing step; when the dyeing step is terminated, the distance between the crystal and the crystal in the film for forming the polarizer in the extending direction is 20 to 40 nm. The dyeing liquid system contains a boric acid compound. By this method, the polarizer can be excellent in polarization, and the durability is remarkably improved even if it is long. Time exposure can also minimize hue changes when exposed to high temperature conditions.

Hereinafter, the present invention will be described in detail.

In general, the method for producing a polarizer comprises a swelling step, a dyeing step, a crosslinking step, an stretching step, a water washing step, and a drying step, and is mainly 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 two stretching methods are mixed may be mentioned. Hereinafter, the method for producing a polarizer of the present invention will be described by way of an example of a wet stretching method, but the method is not limited thereto, except that the steps other than the drying step in the above steps are respectively selected from various solutions in the filling. The bath of one or more types of solutions is immersed in a state of a film for forming a polarizer.

Further, the number of times of the respective steps of the production steps of the polarizer of the present invention, the step conditions, and the like are not particularly limited as long as the object of the present invention is not exceeded.

Hereinafter, a specific example of the method for producing a polarizer of the present invention will be described in more detail.

In the present invention, the polarizer means a general iodine-based polarizer in which a film for forming a polarizer is adsorbed to have iodine.

The film for forming a polarizer is not particularly limited as long as it is a film which can be dyed with a dichroic substance (for example, iodine), and specifically, for example, a polyvinyl alcohol film or a partially saponified polyvinyl alcohol film; a hydrophilic polymer film such as an ethylene terephthalate film, an ethylene-vinyl acetate copolymer film, an ethylene-vinyl alcohol copolymer film, a cellulose film, or a partially saponified film; or a dehydrated film Polyvinyl alcohol thin A film, a polyene alignment film such as a polyvinyl alcohol-based film subjected to hydrochloric acid treatment, or the like. Among these, a polyvinyl alcohol-based film is preferred from the viewpoint of not only enhancing the uniformity of the degree of polarization in the surface but also excellent dyeing affinity for iodine.

<Swelling step>

In the swelling step, the film for forming a polarizer which is not extended is immersed in a swelling tank filled with an aqueous solution for swelling before dyeing, and dust or an antiblocking agent deposited on the surface of the film for forming a polarizer is removed. The step of swelling the film for forming a polarizer to enhance the elongation efficiency and suppressing the dye unevenness, and to improve the physical properties of the polarizer.

In the aqueous solution for swelling, water (pure water, deionized water) may be used alone, and in order to improve the processability of the polymer film, a small amount of glycerin may be added.

When glycerin is contained, the content thereof is not particularly limited, and may be, for example, 5% by weight or less based on the total weight of the aqueous solution for swelling.

The temperature of the swelling tank is not particularly limited and may be, for example, 20 to 45 ° C, preferably 20 to 40 ° C. When the temperature of the swelling tank is within the above range, the subsequent stretching and dyeing efficiency are excellent, and the film expansion caused by excessive swelling can be prevented.

The execution time (swelling tank immersion time) of the swelling step is not particularly limited, and may be, for example, 180 seconds or less, preferably 90 seconds or less. When the immersion time of the swelling tank is within the above range, it is possible to suppress the saturation state due to excessive swelling, and to prevent the softening of the film for forming a polarizer. Cracking, and the adsorption of iodine can be made uniform during the dyeing step to increase the degree of polarization.

The swelling step and the stretching step may be carried out simultaneously, and the elongation ratio may be about 1.1 to 1.7 times, preferably 1.2 to 1.6 times. When the above stretching ratio is less than 1.1 times, wrinkles may occur, and when it exceeds 1.7 times, initial optical characteristics may be lowered.

In the swelling step, an expander roll, a spiral roll, a crown roll, a cloth guider, a bend bar, etc. may be placed in the bath and/or bath. The entrance and exit.

<staining step>

In the dyeing step, a film for forming a polarizer is immersed in a dyeing tank filled with a dyeing liquid containing a dichroic substance (for example, iodine), and a step of adsorbing iodine on the film for forming a polarizer.

In general, in the manufacturing process of a polarizer, a dyeing solution containing iodine and an iodide is immersed in a dyeing step, but in this case, when the transmittance is increased, the degree of polarization cannot be solved. Problems.

However, in the present invention, when the dyeing step is terminated, the distance between the crystal and the crystal in the film for forming a polarizer (the polymer) in the extending direction is set to 20 to 40 nm, preferably 20 to 35 nm, more preferably It is set to 20 to 32 nm, and the dyeing liquid contains a boric acid compound, and the retention time of the boric acid compound is raised before the crosslinking reaction, and the formation ratio of the iodine complex which is a dichroic substance in the film for forming a polarizer is increased. Therefore, the initial polarization degree is made good.

Moreover, according to the production method of the present invention, the crosslinking efficiency of boric acid can be improved, and the degree of stability of the formed complex compound can be improved, and even under high temperature conditions, the amount of decomposition of the complex compound becomes small, and Significantly improve the durability of the polarizer.

Further, the extending direction is preferably in the MD direction. The MD direction is the longitudinal direction (longitudinal direction) of the film for forming a polarizer, and is also the direction in which the film for forming a polarizer is transported in the manufacturing method of the present invention.

When the dyeing step is terminated, the distance between the crystal and the crystal in the film for forming a polarizer in the extending direction can be achieved by adjusting the kind or the elongation ratio of the film for forming a polarizer, and it is preferable to use a dyeing step. The method of adjusting the cumulative elongation ratio at the time of termination to a range of 2.0 to 3.0 times.

The type of the boric acid compound is not particularly limited, and examples of the boric acid compound include boric acid, sodium borate, potassium borate, and lithium borate. These may be used alone or in combination of two or more.

The boric acid compound contained in the dyeing liquid is contained in the dyeing liquid at 0.3 to 5% by weight based on 100% by weight of the dyeing liquid. Within the above range, the content of the PVA-I ₃ complex and the PVA-I ₅ complex can be further increased to lower the risk of fracture.

Further, the boric acid compound in the dyeing liquid may be contained in a lower concentration than the boric acid compound to be added to the crosslinking liquid to be subjected to the crosslinking step.

The dyeing liquid may further contain water, a water-soluble organic solvent or a mixed solvent of these and iodine. The concentration of iodine is relative to the dye solution. It is from 0.4 to 400 mmol/L, preferably from 0.8 to 275 mmol/L, more preferably from 1 to 200 mmol/L.

In order to improve the dyeing efficiency, the dyeing liquid system may further contain an iodide as a co-solvent.

The type of the iodide is not particularly limited, and examples thereof include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, cesium iodide, calcium iodide, and tin iodide. Titanium iodide or the like is preferably potassium iodide from the viewpoint of high solubility in water. These may be used alone or in combination of two or more.

The content of the iodide is not particularly limited, and may be, for example, 0.01 to 10% by weight, preferably 0.1 to 5% by weight, based on 100% by weight of the dyeing liquid.

The temperature of the dyeing tank is not particularly limited and may be, for example, 5 to 42 ° C, preferably 10 to 35 ° C.

The time for immersing the film for forming a polarizer in the dyeing bath is not particularly limited, and may be, for example, 1 to 20 minutes, preferably 2 to 10 minutes.

The stretching step may also be carried out simultaneously with the dyeing step, in which case the elongation ratio may be from 1.2 to 1.76 times.

Further, the cumulative elongation ratio at the end of the dyeing step including the swelling and dyeing step may be 2.0 to 3.0 times as described above. Within the above range, the distance between crystals of the present invention can be achieved, and the problem of occurrence of poor appearance or fragile initial optical characteristics due to wrinkles of the film can be solved.

In this specification, the cumulative extension ratio means in each step The value of the product of the extension ratio.

<Crosslinking step>

The crosslinking step is a step of fixing the dyed polarizer forming film to the cross-linking liquid and adsorbing the iodine molecules, in order to prevent the dyeing property of the physically adsorbed iodine molecules from being lowered by the external environment. .

The cross-linking liquid used in the cross-linking step of the present invention contains a boric acid compound. Thereby, the crosslinking efficiency can be improved to suppress the occurrence of film wrinkles in the step, and the alignment of the dichroic substance can be formed to enhance the optical characteristics.

As the iodine of the dichroic dye, when the crosslinking reaction is disturbed, the iodine molecule is detached due to the moist heat environment, and therefore a sufficient crosslinking reaction is required. Further, in order to enhance the optical characteristics by arranging almost all of the iodine molecules located between the molecules of the polyvinyl alcohol, it is generally necessary to extend at the maximum elongation ratio in the crosslinking step, so the crosslinking step is important.

The crosslinking step of the present invention can be carried out in a single step or in a plurality of steps, and for example, it can be carried out by including at least a first crosslinking step and a second crosslinking step. In the crosslinking step, a boric acid compound may be contained in the crosslinking liquid used in one or more steps. Thereby, the optical characteristics and durability of the polarizer can be simultaneously improved.

The concentration of the boric acid compound in the cross-linking liquid is not particularly limited, but may be, for example, 1 to 10% by weight, preferably 2 to 6% by weight, based on the total weight of the cross-linking liquid. When the concentration of the boric acid compound in the cross-linking liquid is less than 1% by weight, the cross-linking effect is reduced and the alignment property of polyvinyl alcohol and iodine is lowered. When the content exceeds 10% by weight, excessive cross-linking may occur. And a break occurred.

The boric acid compound can be used in the same manner as the user in the dyeing step.

The cross-linking liquid of the present invention may contain water used as a solvent and an organic solvent which is mutually soluble with water, and may be used to prevent the uniformity of the degree of polarization in the surface of the polarizer and the desorption of the dyed iodine. It further contains a small amount of iodide.

The iodide may be used in the same manner as in the dyeing step, and the concentration of the iodide is not particularly limited, and may be, for example, 0.05 to 15% by weight, preferably 0.5 to 0.5% by weight based on the total weight of the crosslinking liquid. 11% by weight. When the concentration of the iodide in the crosslinking tank satisfies the above range, the iodide ions adsorbed in the dyeing step can be prevented from being detached from the film, or the iodide ions contained in the cross-linking liquid can be prevented from penetrating into the film, and the change in the transmittance can be suppressed.

The temperature of the crosslinking tank is not particularly limited, but may be, for example, 20 to 70 °C.

The time for immersing the film for forming a polarizer in the crosslinking groove is not particularly limited, and may be, for example, 1 second to 15 minutes, and preferably 5 seconds to 10 minutes.

The stretching step may also be carried out simultaneously with the crosslinking step. In this case, the stretching ratio of the first crosslinking step may be 1.4 to 3.0 times, preferably 1.5 to 2.5 times. Further, the elongation ratio of the second crosslinking step may be from 1.01 to 2.0 times, preferably from 1.2 to 1.8 times. Further, the cumulative stretching ratio of the first crosslinking step and the second crosslinking step may be 1.5 to 5.0 times, preferably 1.7 to 4.5 times. Within the above range, the increase in crosslinking efficiency can be maintained The effect is that there is no problem that the film is broken due to excessive stretching or the productivity is lowered.

<Complementary Steps>

The method for producing a polarizer of the present invention may further comprise a complementary color step after the crosslinking step, as needed.

In the complementary color step, the film subjected to the crosslinking step is immersed in a complementary color liquid containing a boric acid compound (preferably, a complementary color liquid containing a boric acid compound and an iodide), and the film for polarizing film formation in which the iodine complex is physically adsorbed is placed. The iodine complex of the polyvinyl alcohol intermole is aligned in the vicinity of the cross-linking of the boric acid, whereby the iodine complex is stabilized to adjust the hue. Further, the iodine complex which is not sufficiently adsorbed in the crosslinking step is corrected for the hue of the film for forming a polarizer to be dyed.

The complementary color solution contains water as a solvent and a boric acid compound such as boric acid or sodium borate, and may further contain an organic solvent and an iodide which are mutually soluble in water. The boric acid compound can be used in the same manner as the user in the dyeing step.

The boric acid compound functions to crosslink the polyvinyl alcohol to impart an alignment property, suppress the occurrence of wrinkles in the step, thereby improving handleability and forming an alignment of iodine.

The concentration of the boric acid compound in the above-mentioned complementary color aqueous solution is not particularly limited, but may be, for example, 1 to 10% by weight, preferably 2 to 6% by weight, based on 100% by weight of the complementary color aqueous solution. In the above range, the hue adjustment effect is excellent, and the risk of breakage in the stretching step can be reduced. Sex.

The iodide is used for the purpose of uniformity of the degree of polarization in the plane of the polarizer and prevention of desorption of the dyed iodine, and the iodide can be used in the same manner as in the dyeing step.

The content of the iodide in the above-mentioned complementary color aqueous solution is not particularly limited, but may be, for example, 0.05 to 15% by weight, and preferably 0.5 to 11% by weight based on 100% by weight of the complementary color aqueous solution. Within the above range, it is possible to prevent the iodide ions from being detached and to reduce the transmittance, or the problem that the iodide ions penetrate into the film to reduce the transmittance.

The temperature of the complementary color tank is not particularly limited, but may preferably be 20 to 70 ° C, and the immersion time of the polyvinyl alcohol-based film in the complementary color tank may be 1 second to 15 minutes, preferably 5 seconds to 10 minutes.

The stretching step may be performed simultaneously with the complementary color step. In this case, the complementary color ratio may be from 1.01 to 1.5 times, preferably from 1.02 to 1.08 times. Within the above range, film breakage does not occur, a hue adjustment effect can be exhibited, and productivity is high.

The present invention is preferably extended in such a manner that the total cumulative elongation ratio is 4.0 to 7.0 times.

<Washing step>

The method for producing a polarizer of the present invention may further include a water washing step after the crosslinking step (or the complementary color step) is completed, as needed.

The water washing step is performed by immersing the film for forming a polarizer after cross-linking (or complementary color) in a washing tank filled with a washing liquid, and removing the preceding step. A step of attaching an unnecessary residue to the film for forming a polarizer.

The aqueous solution for water washing may be water (deionized water), and iodide may be further added thereto. The iodide system can be used in the same manner as the user in the dyeing step, and it is preferred to use sodium iodide or potassium iodide.

The content of the iodide is not particularly limited, and may be, for example, 0.1 to 10 parts by weight, preferably 3 to 8 parts by weight, based on the total weight of the aqueous solution for washing.

The temperature of the washing tank is not particularly limited and may be, for example, 10 to 60 ° C, preferably 15 to 40 ° C.

The water washing step may be omitted, or may be performed at the end of each step such as a dyeing step, a crosslinking step, or a complementary color step. In addition, it can be repeated one or more times, and the number of repetitions is not particularly limited.

<drying step>

The drying step is a step of drying the film for forming a water-repellent polarizer, and further improving the alignment of the iodine molecules dyed by the neck-in by drying to obtain a polarizer having excellent optical characteristics. .

The drying method can use natural drying, air drying, heat drying, microwave drying, hot air drying, etc. Recently, microwave treatment which only activates the water in the film to be dried and dried is generally used, and the hot air treatment and the main use are generally used. Infrared processing.

The temperature at the time of hot air drying is not particularly limited, but in order to prevent deterioration of the polarizer, it is preferably carried out at a relatively low temperature, and for example, it may be 20 to 90 ° C, preferably 80 ° C or lower, and more preferably 60 ° C. the following.

The execution time of the hot air drying is not particularly limited, and for example, it can be carried out for 1 to 10 minutes.

<Polarizer and Polarizer>

The present invention provides a polarizing plate produced by the above method and a polarizing plate of at least one area protective film of the polarizing plate manufactured by the above method.

The polarizing plate produced by the above method has a boric acid crosslinking efficiency of 4.5 to 9.0, and the durability can be remarkably improved within the above range, and the hue change can be minimized even when exposed to a high temperature condition for a long period of time.

The type of the protective film is not particularly limited as long as it is excellent in transparency, mechanical strength, thermal stability, moisture shielding property, and the like, and specific examples thereof include poly-pairs. Polyester resin such as ethylene phthalate, polyethylene isophthalate or polybutylene terephthalate; cellulose resin such as diethyl phthalocyanine or triethylene fluorenyl cellulose; Carbonate-based resin; polyacrylic resin such as poly(methyl) acrylate or poly(methyl) acrylate; styrene resin such as polystyrene or acrylonitrile-styrene copolymer; polyethylene, poly a polyolefin resin such as propylene, a polyolefin having a ring system or a decene structure, or an ethylene propylene copolymer; a polyamide resin such as nylon or an aromatic polyamide; a quinone imine resin; and a polyether oxime resin; Lanthanide resin; polyether ketone resin; vulcanized polyphenylene resin; vinyl alcohol resin; vinylidene chloride resin; vinyl butyral resin; aromatic acid ester resin; Methylene resin; thermoplastic resin such as epoxy resin Into the film, the film may also be used in the blend of the thermoplastic resin composed of. Also, you can use A film composed of a thermosetting resin such as a (meth)acrylic acid, an urethane-based compound, an epoxy resin or a fluorene-based resin, or an ultraviolet curable resin. Among them, in particular, a cellulose-based film having a surface saponified by an alkali or the like is particularly preferable in consideration of polarization characteristics or durability. Further, the protective film may be a function having the following optical layer.

The structure of the polarizing plate described above is not particularly limited, and various optical layers satisfying desired optical characteristics may be laminated on the polarizing plate. For example, it may be a structure having a structure in which a protective film of a polarizer is protected on at least one area of a polarizer; a hard coat layer, an anti-reflection layer, an anti-adhesion layer, and an anti-reflection layer are laminated on at least one side of the polarizer or the protective film. a structure of a surface treatment layer such as a diffusion layer or an anti-glare layer; a structure of an alignment liquid crystal layer or other functional film which compensates for a viewing angle on at least one side of the polarizer or the protective film. Further, it may be an optical film, a reflector, a semi-transmissive plate, or a wavelength plate including a 1⁄2 wavelength plate or a 1⁄4 wavelength plate used in a polarizing conversion device to be used in forming various image display devices. One or more layers of the phase difference plate (including the λ plate), the viewing angle compensation film, and the brightness enhancement film are configured as an optical layer. More specifically, in the case of a polarizing plate having a structure of a protective film of an area of a polarizer, a reflective polarizing plate or a semi-reflective reflector or a semi-transparent reflector is preferably laminated on the laminated protective film. A penetrating polarizing plate; a circular or circular polarizing plate of a laminated phase difference plate; a wide viewing angle polarizing plate for a laminated viewing angle compensation layer or a viewing angle compensation film; or a polarizing plate for stacking a brightness enhancement film.

Such a polarizing plate can be applied not only to a general liquid crystal display device but also to various image display devices such as an electric field light-emitting display device, a plasma display device, and an electric field radiation display device.

In the following, in order to facilitate the understanding of the present invention, the preferred embodiments are presented, but the embodiments are merely illustrative of the present invention and are not intended to limit the scope of the patent application of the accompanying claims. Various changes and modifications can be made to the embodiments within the scope of the invention and the scope of the invention. Of course, such variations and modifications are also within the scope of the appended claims.

Examples and comparative examples

(1) Embodiment 1

A transparent unstretched polyvinyl alcohol (PVA) film (PE60, KURARAY Co., Ltd.) 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, and then contained 1.25 mmol of iodine. /L, 1.25 wt% of potassium iodide and 0.3% by weight of boric acid were dyed in an aqueous solution for dyeing at 30 ° C for 2 minutes and 30 seconds. At this time, the swelling and dyeing steps were carried out at an extension ratio of 1.56 times and 1.64 times, respectively, and the cumulative stretching ratio after passing through the dyeing tank was 2.56 times. Then, it was immersed for 26 seconds (first crosslinking step) in an aqueous solution for cross-linking containing 56.9% by weight of potassium iodide and 3% by weight of boric acid (cross-linking step), and was stretched at a stretching ratio of 1.7 times. Thereafter, the mixture was immersed in an aqueous solution for cross-linking containing 56.9% by weight of potassium iodide and 3% by weight of boric acid at 56° C. for 20 seconds (second crosslinking step) to be crosslinked, and further stretched at an extension ratio of 1.34 times. Then, it was immersed in an aqueous solution for complementary color containing 40% by weight of potassium iodide and 2% by weight of boric acid for 10 seconds while extending 1.01 times.

At this point, the total of the swelling, dyeing and cross-linking, complementary steps The cumulative extension ratio is six times. After the completion of the crosslinking, a polyvinyl alcohol (PVA) film was dried in an oven at 70 ° C for 4 minutes to prepare a polarizer.

A polarizing plate was produced by using a two-area layer of triacetyl cellulose (TAC) film of the produced polarizer.

(2) Examples 2 to 7 and Comparative Examples 1 to 3

A polarizing plate was produced in the same manner as in Example 1 except for the boric acid concentration in the dyeing tank described in Table 1 below, the elongation ratio in the swelling step, the elongation ratio in the dyeing step, and the cumulative elongation ratio after passing through the dyeing tank.

For reference, the polarizers of the above examples and comparative examples are all manufactured to have a high transmittance (43.5%), and the following are comparative physical properties.

Analysis example

The physical properties (crosslinking efficiency and distance between crystal and crystal in the PVA film) of the polarizing plates produced in the above Examples and Comparative Examples were measured by the following methods, and the results are shown in Table 1 below.

Crosslinking efficiency 1.1 Crosslinking degree

The central portion of the polarizer produced in the examples and the comparative examples was cut into a size of 10 cm × 10 cm, and then the degree of crosslinking was measured using a Nicolet 5700 (FT-IR) apparatus of Thermo Fisher Scientific.

The FT-IR wafer was a VeeMAX III (ATR) from Pike Technologies, and the number of scans was 16 and the resolution was 4 cm ^-1 . Further, in the measured IR data, after the area (a) of the region of 2850 to 3000 cm ^-1 is set as the reference peak area (a) with reference to 3.2, the area of 1200 to 1360 cm ^-1 is divided by the reference spectrum. Peak area (a).

Crosslinking degree = (area of 1200~1360cm ^-1 ) / (reference peak area (a))

After the above-described measurement method of the degree of crosslinking was carried out three times, the average value was determined.

1.2 Boron analysis

0.15 g of the sample of the polarizer sample produced in the examples and the comparative examples was placed in a vial, and ultrapure water was further added to make the sample weight 25 g, and the vial was placed in a thermostat at 90 ° C. After the polarizer sample is completely dissolved, it is left to cool.

To the sample to be cooled, 20 mL of a mannitol solution was added, and the mixture was titrated with 0.1 N NaOH to determine a boron content (%).

1.3 Crosslinking efficiency

Using the obtained degree of crosslinking and the boron content, the crosslinking efficiency was calculated according to the following formula.

Crosslinking efficiency: degree of crosslinking / boron content (%)

2. The distance between crystallization and crystallization in PVA (long period)

Samples were taken at a X-ray wavelength of 1.567 angstroms (Å) using a Posco Accelerator Research Institute (PAL) synchrotron beam (Synchrotron Beam) The distance to the director was set to 3.0 m, and the distance between the crystal in the extending direction of the PVA obtained by the cumulative stretching ratio of the dyeing tank and the crystal was measured by the beam path of 1 mm and the peak of the scattering vector q.

The distance between crystal and crystal in PVA (long period, d) = 2 π / q

Test case

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.

Optical characteristics (1) Polarization, A700, A480

After the produced polarizer was cut into a size of 4 cm × 4 cm, the transmittance was measured using an ultraviolet visible ray spectrometer (V-7100, manufactured by JASCO Corporation). At this time, the degree of polarization is defined by the following formula 1.

For reference, the degree of polarization must be noted that even a difference of about 0.001 will have a significant impact on the contrast ratio. If the degree of polarization is less than 99.990, the contrast ratio will decrease, and it is difficult to achieve real black.

[Equation 1] Polarization degree (P) = [(T _{1 -} T ₂ ) / (T ₁ + T ₂ )] ^1/2 × 100

Further, the unit of the degree of polarization (P) is %.

(In the formula, T ₁ is a pair of polarizers arranged such that the parallel transmittance of the absorption axis is parallel, and T ₂ is a pair of polarizers arranged such that the absorption axis is orthogonal. Orthogonal penetration rate).

A 700 and A 480 are absorbances defined by Equations 2 and 3.

[Expression 2] A 700=-Log ₁₀ {(T _MD,700 ×T _TD,700 )/10000}

(In the formula, T _{MD, 700} is a polarizing plate manufactured such that the transmittance of the polarizing plate is such that the absorption axis of the polarizing plate is orthogonal to the linear polarization of the measuring light, and the transmittance of 700 nm wavelength is obtained, T _{TD, 700} is The polarizing plate to be produced is disposed such that the transmittance of the wavelength of 700 nm obtained when the absorption axis of the polarizing plate is parallel to the linear polarization of the measuring light, and the units are all %).

[Expression 3] A 480=-Log ₁₀ {(T _MD,480 ×T _TD,480 )/10000}

(In the formula, _{TMD, 480} is a polarizing plate produced by arranging the transmittance of 480 nm obtained when the absorption axis of the polarizing plate is orthogonal to the linear polarization of the measurement light, T _{TD, 480} is The polarizing plate to be produced is disposed such that the transmittance at a wavelength of 480 nm obtained when the absorption axis of the polarizing plate is parallel to the linear polarization of the measurement light, and the units are all %).

PVA-I ₅ complex (a complex of PVA and I ₅ ^- ) and a PVA-I ₃ complex (a complex of PVA and I ₃ ^- ) when the absorbance values of A 700 and A 480 are higher. The higher content means higher polarization.

2. Evaluation of heat resistance

The spectrophotometer (V7100, Japan Spectrophotometer) was used to measure the spectral transmittance τ(λ) of the polarizing plate produced in the examples and the comparative examples at 30 ° C for 30 minutes and after standing for 30 minutes, and the result was determined. The cross-beam light was transmitted through the spectrum, and A 700 shown in the above formula 2 was obtained.

After the above heat resistance evaluation, it was confirmed by visual observation to confirm whether or not the polarizing plate was red-colored. In Table 1, the X system indicates that no red transition occurred, and the O system indicates that red transition occurred.

Referring to Table 2 above, the polarizers produced by the methods of Examples 1 to 10 exhibited excellent optical characteristics, and after the heat resistance test, high absorbance was also exhibited, and no reddening occurred. However, the optical characteristics of the polarizer produced by the methods of Comparative Examples 1 to 5 were deteriorated, and the absorbance after the heat resistance test was low, and a red phenomenon was caused substantially.

Claims (11)

A method for producing a polarizer comprising the steps of swelling, dyeing, crosslinking and stretching of a film for forming a polarizer; wherein the swelling step, the dyeing step, and the crosslinking step are performed in this order; At least a part is carried out in the dyeing step and/or before the dyeing step; when the dyeing step is terminated, the distance between the crystal and the crystal in the film for forming the polarizer in the extending direction is 20 to 40 nm; Contains a boric acid compound. The method for producing a polarizer according to claim 1, wherein the extending direction is an MD direction. The method for producing a polarizer according to claim 1 or 2, wherein the boric acid compound is contained in the dyeing liquid in an amount of 0.3 to 5% by weight based on the total weight of the dyeing liquid. The method for producing a polarizer according to any one of claims 1 to 3, wherein the cumulative elongation ratio until the termination of the dyeing step is 2.0 to 3.0 times. The method for producing a polarizer according to any one of claims 1 to 4, wherein the crosslinking step includes at least a first crosslinking step and a second crosslinking step. The method for producing a polarizer according to any one of claims 1 to 5, wherein the concentration of the boric acid compound in the dyeing liquid in the dyeing step is lower than the boric acid in the cross-linking liquid in the crosslinking step. Chemical The concentration of the compound. The method for producing a polarizer according to any one of claims 1 to 6, further comprising a complementary color step. A polarizer is manufactured by the method of any one of claims 1 to 7. The polarizer according to claim 8, wherein the boric acid crosslinking efficiency is from 4.5 to 9.0. A polarizing plate comprising the polarizer according to claim 8 and a protective film laminated on at least one side of the polarizer. An image display device comprising the polarizing plate according to claim 10 of the patent application.