WO2016047554A1

WO2016047554A1 - Method for manufacturing polarizer

Info

Publication number: WO2016047554A1
Application number: PCT/JP2015/076509
Authority: WO
Inventors: 天煕趙; 容鉉權; 民奎朴; 佑煥薛; 公彦矢可部; 佑介北河
Original assignee: 住友化学株式会社
Priority date: 2014-09-23
Filing date: 2015-09-17
Publication date: 2016-03-31
Also published as: CN107076906B; TWI663435B; KR20160035516A; JPWO2016047554A1; TW201617647A; KR102450760B1; KR20170058948A; JP6694821B2; CN107076906A

Abstract

The present invention relates to a method for manufacturing a polarizer, and more specifically, the present invention includes steps for swelling, dyeing, crosslinking, and drawing a film for forming the polarizer. The swelling step, dyeing step, and cross-linking step are carried out in this order. At least part of the drawing step is carried out in the dyeing step and/or before the dyeing step. When the dyeing step is completed, distance between crystals in the film for forming the polarizer in the drawing direction is 20 - 40 nm. The dyeing solution includes a boric acid compound.

Description

Manufacturing method of polarizer

The present invention relates to a method for manufacturing a polarizer.

Used in various image display devices such as liquid crystal display (LCD), electroluminescence (EL) display, plasma display (PDP), field emission display (FED), organic light emitting diode (OLED), etc. A polarizing plate generally includes a polarizer in which an iodine compound or a dichroic polarizing material is adsorbed and oriented on a polyvinyl alcohol (PVA) film, and a polarizer protective film is provided on one surface of the polarizer. The other surface of the polarizer has a multilayer structure in which a polarizer protective film, an adhesive layer bonded to a liquid crystal cell, and a release film are sequentially stacked.

The polarizer constituting the polarizing plate is required to have high transmittance and degree of polarization in order to be applied to an image display device and provide an image having excellent color reproducibility. In addition, as the application of flat panel display devices to various fields spreads and the trend toward larger size becomes more prominent, various image display devices such as liquid crystal display devices may be used for a long time at high temperatures. As a result, the demand for improvement in durability along with improvement in polarization performance and optical performance has increased, and as a result, the conditions for the performance of the polarizing plate have become very strict. In addition, image display devices having characteristics suitable for various environments and applications are currently being sought, and optical durability including hue change under high temperature and high humidity conditions, and high contrast through high orientation and high transmission. It has been demanded.

Korean Patent No. 1296786 discloses a method of manufacturing a polarizer, but when the transmittance is high, the problem that the degree of polarization decreases cannot be improved.

Korean Patent No. 1296786

An object of the present invention is to provide a method capable of producing a polarizer having improved optical characteristics and durability.

1. Including swelling, dyeing, crosslinking and stretching steps of the polarizer-forming film,
The swelling step, the dyeing step, and the crosslinking step are performed in this order,
At least a part of the stretching step is performed in the dyeing step and / or before the dyeing step;
At the end of the dyeing step, the distance between crystals in the polarizer-forming film in the stretching direction is 20 to 40 nm, and the dyeing solution contains a boric acid compound.

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

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

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

5. In 1 above, the cross-linking step includes at least a first cross-linking step and a second cross-linking step.

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

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

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

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

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

11. An image display apparatus comprising the ten polarizing plates.

The method of the present invention can produce a polarizer having improved optical properties and improved polarization degree while having high transmittance.
The method of the present invention can produce a polarizer with significantly improved durability.
Also, the method of the present invention can minimize the hue change even when exposed to high temperature conditions for a long time.

The present invention includes a step of swelling, dyeing, crosslinking and stretching a film for forming a polarizer, wherein the swelling step, the dyeing step, and the crosslinking step are performed in this order, and at least a part of the stretching step includes Performed at the end of the dyeing step and / or before the dyeing step, and at the end of the dyeing step, the distance between the crystals in the polarizer forming film in the stretching direction is 20 to 20 Production of a polarizer that is 40 nm, and the dyeing solution contains a boric acid compound, which has excellent polarization degree, significantly improved durability, and can minimize hue change even when exposed to high temperature conditions for a long time. Regarding the method.

Hereinafter, the present invention will be described in detail.

Usually, a method for producing a polarizer includes a swelling step, a dyeing step, a crosslinking step, a stretching step, a water washing step, and a drying step, and is classified mainly 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, the method for producing a polarizer of the present invention will be described by taking a wet stretching method as an example. However, the present invention is not limited to this, and the other steps except the drying step in the above steps are different types of solutions. It is performed in a state where the film for forming a polarizer is immersed in a thermostatic water bath filled with one or more solutions selected from the inside.

In addition, the number of repetitions of each manufacturing step of the polarizer of the present invention, process conditions, and the like are not particularly limited as long as they do not depart from the object of the present invention.

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

In the present invention, a polarizer means a normal iodine-based polarizer in which iodine is adsorbed and oriented on a polarizer-forming film.

The type of the polarizer-forming film is not particularly limited as long as it is a film that can be dyed with a dichroic material such as iodine. Specifically, a polyvinyl alcohol film, a partially saponified polyvinyl alcohol film; polyethylene terephthalate Hydrophilic polymer films such as films, ethylene-vinyl acetate copolymer films, ethylene-vinyl alcohol copolymer films, cellulose films, partially saponified films thereof; or dehydrated polyvinyl alcohol systems Examples thereof include a polyene oriented film such as a film and a polyvinyl alcohol film subjected to dehydrochlorination treatment. 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.

<Swelling step>
In the swelling step, impurities such as dust and anti-blocking agents deposited on the surface of the polarizer-forming film are immersed in a swelling tank filled with a swelling aqueous solution before dyeing the unstretched polarizer-forming film. This is a step for improving the physical properties of the polarizer by removing the swell and improving the stretching efficiency by swelling the polarizer-forming film and also suppressing the unevenness of dyeing.

As the aqueous solution for swelling, usually water (pure water, deionized water) may be used alone, or a small amount of glycerin may be added to improve the processability of the polymer film.

When glycerin is included, the content is not particularly limited, and may be, for example, 5% by weight or less of 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 a swelling tank is in said range, it is excellent in subsequent extending | stretching and dyeing | staining efficiency, and can prevent the expansion of the film by excessive swelling.

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

The swelling step and the stretching step may be performed simultaneously. In this case, the stretching ratio may be about 1.1 to 1.7 times, preferably 1.2 to 1.6 times. When the draw ratio is less than 1.1 times, wrinkles may occur, and when it exceeds 1.7 times, the initial optical properties may be deteriorated.
In the swelling step, an expander roll, a spiral roll, a crown roll, a cross guider, a bend bar or the like may be provided in the bath and / or at the entrance / exit of the bath.

<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, a dyeing solution containing iodine, and adsorbing iodine to the polarizer forming film.

Usually, it is immersed in a dyeing solution containing iodine and iodide in the dyeing step of the manufacturing process of the polarizer. At this time, when manufacturing so as to increase the transmittance, it cannot be solved that the degree of polarization decreases. There was a problem.

However, in the present invention, at the end of the dyeing step, the distance between the crystals in the polarizer-forming film (polymer) in the stretching direction is 20 to 40 nm, preferably 20 to 35 nm, more preferably 20 to 32 nm, the dyeing solution contains a boric acid compound, the residence time of the boric acid compound is improved before the cross-linking reaction, and the formation rate of the complex of iodine which is a dichroic substance in the polarizer forming film is increased. By increasing the value, the initial polarization degree is improved.

In addition, according to the production method of the present invention, the boric acid crosslinking efficiency is increased, the stability of the formed complex is improved, the amount of complex decomposition is reduced even under high temperature conditions, and the durability of the polarizer can be remarkably improved. .

The stretching direction is preferably the MD direction. The MD direction is the longitudinal direction (longitudinal direction) of the polarizer-forming film, and is also the transport direction of the polarizer-forming film in the production method of the present invention.

At the end of the dyeing step, the distance between the crystals in the polarizer-forming film in the stretching direction can be achieved through adjustment of the type of polarizer-forming film and the stretching ratio, preferably the dyeing step A method of adjusting the cumulative stretch ratio at the end to a range of 2.0 to 3.0 times can be used.

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 admixture of two or more.

The boric acid compound contained in the staining solution may be contained in the staining solution at 0.3 to 5% by weight with respect to 100% by weight of the staining solution. Within the above range, the content of the PVA-I ₃ complex and the PVA-I ₅ complex can be further increased, and the risk of cleavage is reduced.

Also, the boric acid compound in the dyeing solution may be included so as to have a lower concentration than the boric acid compound added to the crosslinking solution in the subsequent crosslinking step.

The staining solution may further contain water, a water-soluble organic solvent, or a mixed solvent thereof and iodine. The iodine concentration may be 0.4 to 400 mmol / L, preferably 0.8 to 275 mmol / L, more preferably 1 to 200 mmol / L with respect to the staining solution.

The staining solution may further contain iodide as a solubilizing agent for improving the staining efficiency.

The type of iodide is not particularly limited. For example, potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide. And titanium iodide, and potassium iodide is preferred in that it has high solubility in water. These may be used alone or in admixture 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, out of 100% by weight of the staining solution.

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

The stretching step may be performed simultaneously with the dyeing step, and the stretching ratio in this case is preferably 1.2 to 1.76 times.

Further, as described above, the cumulative draw ratio at the end of the dyeing step including the swelling and dyeing steps may be 2.0 to 3.0 times. The distance between the crystals according to the present invention can be realized within the above range, and the problem that the film is wrinkled to cause poor appearance or the initial optical characteristics are fragile can be solved.

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

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

The crosslinking liquid used in the crosslinking step of the present invention contains a boric acid compound. Through this, it is possible to improve the cross-linking efficiency, suppress the generation of wrinkles of the film during the process, and form the orientation of the dichroic material to improve the optical characteristics.

Since iodine, which is a dichroic dye, has an unstable crosslinking reaction, iodine molecules may be detached by a moist heat environment, so that a sufficient crosslinking reaction is required. In addition, in order to improve the optical properties by orienting almost all iodine molecules located between the polyvinyl alcohol molecules, the cross-linking step is important because the cross-linking step generally has to be stretched with the largest stretch ratio. .

The crosslinking step according to the present invention may be performed in a single step or a plurality of steps, for example, may include at least a first crosslinking step and a second crosslinking step. A boric acid compound may be included in the crosslinking liquid used in one or more of the crosslinking steps. Thereby, the optical characteristic and durability of a polarizer can be improved simultaneously.

The concentration of the boric acid compound in the crosslinking 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 crosslinking liquid. When the concentration of the boric acid compound in the crosslinking liquid is less than 1% by weight, the crosslinking effect may decrease and the orientation of polyvinyl alcohol and iodine may decrease. Cutting can occur.

The same boric acid compound as that used in the staining step can be used.

The crosslinking liquid of the present invention may contain water used as a solvent and an organic solvent that can be mutually dissolved together with water, in order to prevent the uniformity of the degree of polarization in the plane of the polarizer and the desorption of dyed iodine. A small amount of iodide may also be included.

The iodide used may be the same as that used in the dyeing step, and the concentration of the iodide is not particularly limited, and is, for example, 0.05 to 15% by weight of the total weight of the crosslinking solution. Preferably 0.5 to 11% by weight. When the iodide concentration in the crosslinking tank satisfies the above range, it prevents the iodine ions adsorbed in the dyeing step from desorbing from the film or penetrating the film from iodine ions contained in the crosslinking solution. The rate change 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 polarizer forming film in the crosslinking tank is not particularly limited, and may be, for example, 1 second to 15 minutes, preferably 5 seconds to 10 minutes.

The stretching step may be performed simultaneously with the crosslinking step, in which case the stretching ratio of the first crosslinking step may be 1.4 to 3.0 times, preferably 1.5 to 2.5 times. It is good. Further, the draw ratio of the second crosslinking step may be 1.01 to 2.0 times, and preferably 1.2 to 1.8 times. In addition, 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 effect of increasing the crosslinking efficiency can be maintained, and there is no problem that the film is broken or the production efficiency is lowered due to excessive stretching.

<Complementary color step>
If necessary, the method for producing a polarizer of the present invention may further include a complementary color step after the crosslinking step.

In the complementary color step, the film having undergone the crosslinking step is immersed in a complementary color solution containing a boric acid compound, preferably a complementary color solution containing a boric acid compound and iodide, and the iodine complex is physically adsorbed. By orienting the iodine complex located between the polyvinyl alcohol molecules of the polarizer-forming film in the vicinity of the boric acid bridge, the iodine complex is stabilized and the hue is adjusted. Moreover, the hue with respect to the film for polarizer formation dye | stained the iodine complex which is not fully adsorb | sucked by the bridge | crosslinking step is correct | amended.

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

The boric acid compound plays a role in forming orientation of iodine by crosslinking polyvinyl alcohol to impart orientation and suppressing wrinkle generation in the process to improve handleability.

The concentration of the boric acid compound in the complementary color aqueous solution is not particularly limited, but may be, for example, 1 to 10% by weight, preferably 2 to 6% by weight with respect to 100% by weight of the complementary color aqueous solution. The hue control effect is very excellent within the above range, and the risk of cutting during the stretching process can be reduced.

The iodide is used to prevent the depolarization of the uniformity of the degree of polarization in the plane of the polarizer and the dyed iodine, and the same iodide as that used in the dyeing step can be used. .

The iodide content in the complementary color aqueous solution is not particularly limited. For example, it may be 0.05 to 15% by weight, preferably 0.5 to 11% by weight, based on 100% by weight of the complementary color aqueous solution. Good. Within the above range, it is possible to prevent the problem that iodine ions are desorbed and the transmittance is reduced, or that iodine ions penetrate into the film and the transmittance is reduced.

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 film in the complementary color tank may be 1 second to 15 minutes, preferably 5 seconds to 10 It should be minutes.

The stretching step may be performed simultaneously with the complementary color step, and at this time, the stretching ratio of the complementary color step may be 1.01 to 1.5 times, preferably 1.02 to 1.08 times. . Within the above range, the hue adjusting effect can be shown without breaking the film, and the production efficiency is high.

The present invention is preferably stretched so that the total cumulative stretching ratio is 4.0 to 7.0 times.

<Washing step>
If necessary, the method for producing a polarizer of the present invention may further include a water washing step after the crosslinking step (or complementary color step) is completed.

The water washing step is a step of immersing the film for forming a polarizer having undergone crosslinking (or complementary color) in a water washing tank filled with a water washing solution, and removing unnecessary residues attached to the film for forming a polarizer in the previous step. It is.

The aqueous solution for washing may be water (deionized water), and an iodide may be further added thereto. As the iodide, the same ones used in the dyeing step can be used, and among these, sodium iodide or potassium iodide is preferably used.

The content of 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 washing solution.

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 can be omitted, and may be performed each time a previous step such as a dyeing step, a crosslinking step, or a complementary color step is completed. Moreover, it may 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 washed polarizer-forming film and further improving the orientation of iodine molecules dyed by neck-in by drying to obtain a polarizer having excellent optical properties.

As drying methods, methods such as natural drying, air drying, heat drying, microwave drying, hot air drying and the like can be used. Recently, a new microwave treatment that activates and dries only the water in the film has been newly introduced. In general, hot air treatment and far-infrared treatment are mainly used.

Although the temperature at the time of hot air drying is not particularly limited, it 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 80 ° C. or less, more preferably Is preferably 60 ° C. or lower.

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

<Polarizer and polarizing plate>
The present invention provides a polarizer produced by the above method and a polarizing plate in which a protective film is laminated on at least one surface of the polarizer produced by the above method.

The polarizer manufactured by the above method may have a boric acid crosslinking efficiency of 4.5 to 9.0, and the durability is remarkably improved within the above range, and also when exposed to high temperature conditions for a long time. Hue change can be minimized.

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; cellulose resins such as diacetylcellulose and triacetylcellulose; polycarbonate resins; polyacrylic resins such as polymethyl (meth) acrylate and polyethyl (meth) acrylate; polystyrene and acrylonitrile Styrenic resins such as styrene copolymers; Polyolefin resins such as polyethylene, polypropylene, cyclo- or polyolefin having a norbornene structure, and ethylene-propylene copolymers; Polyamides such as nylon and aromatic polyamides Fatty resin; imide resin; polyethersulfone resin; sulfone resin; polyetherketone resin; sulfide polyphenylene resin; vinyl alcohol resin; vinylidene chloride resin; vinyl butyral resin; Resin; a film composed of a thermoplastic resin such as an epoxy resin may be mentioned, and a film composed of a blend of the thermoplastic resin may also be used. Moreover, you may use the film which consists of thermosetting resins, such as (meth) acrylic-type, urethane type, an epoxy type, a silicon type, or ultraviolet curable resin. Among these, a cellulose-based film having a surface soaped (saponified) by alkali or the like is particularly preferable in consideration 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 optical layers satisfying necessary optical characteristics may be laminated on the polarizer. For example, a structure in which a protective film for protecting the polarizer is laminated on at least one surface of the polarizer; a hard coat layer, an antireflection layer, an anti-adhesion layer, a diffusion prevention layer on at least one surface of the polarizer or the protective film A structure in which a surface treatment layer such as an antiglare layer is laminated; a structure in which an alignment liquid crystal layer or other functional film for compensating a viewing angle is laminated on at least one surface of a polarizer or a protective film. There may be. In addition, wave plates (including λ plates) such as optical films such as polarization conversion devices, reflectors, semi-transmissive plates, half-wave plates, or quarter-wave plates used to form 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, as a polarizing plate having a structure in which a protective film is laminated on one surface of a polarizer, 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; An elliptical or circular polarizing plate on which a phase difference 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 is preferable.

Such a polarizing plate is applicable not only to a normal liquid crystal display device but also to various image display devices such as an electroluminescence display device, a plasma display device, and a field emission display device.

In the following, preferred examples are presented to aid the understanding of 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 scope and the technical idea, and such changes and modifications are also within the scope of the appended claims.

Examples and Comparative Examples (1) Example 1
A transparent unstretched polyvinyl alcohol (PVA) film (PE60, KURARAY) having a saponification degree of 99.9% or more was swelled by being immersed in water (deionized water) at 25 ° C. for 1 minute and 20 seconds, Dyeing was performed by immersing in an aqueous dyeing solution at 30 ° C. containing 1.25 mmol / L of iodine, 1.25% by weight of potassium iodide and 0.3% by weight of boric acid for 2 minutes and 30 seconds. At this time, the film was stretched at a stretching ratio of 1.56 times and 1.64 times in the swelling and dyeing steps, respectively, and stretched so that the cumulative stretching ratio after passing through the dyeing tank was 2.56 times. Subsequently, the film was immersed in an aqueous solution for crosslinking at 56 ° C. containing 13.9% by weight of potassium iodide and 3% by weight of boric acid for 26 seconds (first crosslinking step) while being crosslinked for a stretching ratio of 1.7 times. And stretched. Thereafter, the film was immersed in an aqueous solution for crosslinking at 56 ° C. containing 13.9% by weight of potassium iodide and 3% by weight of boric acid for 20 seconds (second crosslinking step) and crosslinked at a stretch ratio of 1.34 times. Stretched. Subsequently, the film was stretched 1.01 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 for 10 seconds.

At this time, the total cumulative draw ratio of the swelling, dyeing and crosslinking, and complementary color steps was set to 6 times. After the completion of crosslinking, a polyvinyl alcohol (PVA) film was dried in an oven at 70 ° C. for 4 minutes to produce a polarizer.

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

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

The polarizing plate was formed in the same manner as in Example 1 except for the boric acid concentration in the dyeing tank, the stretching ratio of the swelling step, the stretching ratio of the dyeing step, and the cumulative stretching ratio after passing through the dyeing tank described in Table 1 below. Manufactured.

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

Analysis example

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

1. Crosslinking efficiency 1.1 Crosslinking degree After the central part of the polarizer produced in Examples and Comparative Examples was cut to a size of 10 cm × 10 cm, the crosslinking degree was measured using a Nicolet 5700 (FT-IR) apparatus manufactured by Thermo Fisher Scientific. Was measured.

As an FT-IR chip, VeeMAX III (ATR) manufactured by Pike technologies was used, and the number of scans was 16 times and the resolution was 4 cm ⁻¹ . Further, in the measured IR Data, the area (a) of the 2850 to 3000 cm ⁻¹ region is adjusted to the standard Peak area (a) by matching the standard of 3.2, and then the area of 1200 to 1360 cm ⁻¹ is the standard Peak area. Divide by (a).

Crosslinking degree = (area of 1200 to 1360 cm ⁻¹ ) / (reference peak area (a))
After performing the above-mentioned method for measuring the degree of crosslinking three times, an average value is obtained.

1.2 Boron analysis 0.15 g of the polarizer sample produced in the examples and comparative examples was put in a vial, ultrapure water was added to make the sample weight 25 g, and the vial was put in a thermostat at 90 ° C. The polarizer sample is completely dissolved and then allowed to cool.
Add 20 mL of mannitol solution to the cooled sample and titrate with 0.1 N NaOH to obtain the Boron content (%).

1.3 Crosslinking efficiency Using the obtained degree of crosslinking and the Boron content, the crosslinking efficiency is calculated according to the following equation.
Crosslinking efficiency: degree of crosslinking / Boron content (%)

2. Distance between crystals in PVA (Long Period)
Using the Synchrotron Beam from Pohang Accelerator Laboratory (PAL), the X-ray wavelength of 1.567 angstroms, the distance from the sample to the director is 3.0 m, the beam path is 1 mm, and the inside of the PVA is 1 mm. The distance between the crystals in the stretching direction was measured based on the peak of the scattering vector q.
Distance between crystals in PVA (Long Period, d) = 2π / q

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 characteristics (1) Polarization degree, A700, A480
The manufactured polarizer was cut into a size of 4 cm × 4 cm, and 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 1 below.

For reference, it should be noted that a difference of about 0.001 in the degree of polarization greatly affects the contrast ratio. When the degree of polarization is less than 99.990, the contrast ratio is lowered and it is difficult to realize real black.

[Formula 1]
Polarization degree (P) = [(T ₁ −T ₂ ) / (T ₁ + T ₂ )] ^1/2 × 100
The unit of polarization degree (P) is%.
(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).

A700 and A480 are absorbances defined by Equations 2 and 3.
[Formula 2]
A700 = −Log ₁₀ {(TMD _{, 700} × _{TTD, 700} ) / 10000}
(In the formula, _{TMD, 700} is a transmittance at a wavelength of 700 nm obtained when the manufactured polarizing plate is disposed in a state where the absorption axis of the polarizing plate is orthogonal to the linearly polarized light of the measuring light, and T _{TD, 700} is a transmittance at a wavelength of 700 nm obtained when the manufactured polarizing plate is arranged in a state where the absorption axis of the polarizing plate is parallel to the linearly polarized light of the measuring light, and these units are%. ).

[Formula 3]
A480 = −Log ₁₀ {(TMD _{, 480} × _{TTD, 480} ) / 10000}
(In the formula, _{TMD, 480} is a transmittance at a wavelength of 480 nm obtained when the manufactured polarizing plate is disposed in a state where the absorption axis of the polarizing plate is orthogonal to the linearly polarized light of the measuring light, and T _{TD , 480} is the transmittance at a wavelength of 480 nm obtained when the manufactured polarizing plate is arranged in a state where the absorption axis of the polarizing plate is parallel to the linearly polarized light of the measuring light, and these units are all in%. is there).

When A700 and A480 value of absorbance is high, _{PVA-I 5} complex (PVA and _{I 5} ^- the complex) and _{PVA-I 3} complex (PVA and _{I 3} ^- complexes) high content of, degree of polarization is high Means.

2. Evaluation of heat resistance Spectral transmittance τ (λ) measured before and after leaving the polarizing plate produced in Examples and Comparative Examples at 105 ° C. for 30 minutes was measured with a spectrophotometer (V7100, JASCO Corporation). Then, the orthogonal spectral transmission spectrum was obtained from this result, and A700 represented by the above formula 2 was obtained.

After the heat resistance evaluation, the presence or absence of red discoloration of the polarizing plate was confirmed by visual observation. In Table 1, X indicates that redness did not occur, and O indicates that redness occurred.

Referring to Table 2 above, the polarizers produced by the methods of Examples 1 to 10 exhibited excellent optical characteristics, showed relatively high absorbance even after the heat resistance test, and did not cause a red discoloration phenomenon. However, the polarizers produced by the methods of Comparative Examples 1 to 5 were somewhat inferior in optical properties and had a lower absorbance after the heat resistance test, and generally a reddish phenomenon occurred.

Claims

Including swelling, dyeing, crosslinking and stretching steps of the polarizer-forming film,
The swelling step, the dyeing step, and the crosslinking step are performed in this order,
At least a part of the stretching step is performed in the dyeing step and / or before the dyeing step;
At the end of the dyeing step, the distance between the crystals in the polarizer-forming film in the stretching direction is 20 to 40 nm,
The method for producing a polarizer, wherein the staining liquid contains a boric acid compound.
The method for producing a polarizer according to claim 1, wherein the stretching 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 a staining solution in an amount of 0.3 to 5% by weight of the total weight of the staining solution.
The method for producing a polarizer according to any one of claims 1 to 3, wherein a cumulative stretch ratio until the end 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 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 staining liquid in the staining step is lower than the concentration of the boric acid compound in the crosslinking liquid in the crosslinking step.
The method for producing a polarizer according to any one of claims 1 to 6, further comprising a complementary color step.
A polarizer manufactured by the method according to any one of claims 1 to 7.
The polarizer according to claim 8, wherein the boric acid crosslinking efficiency is 4.5 to 9.0.
A polarizing plate comprising the polarizer of claim 8 and a protective film laminated on at least one surface of the polarizer.
An image display device comprising the polarizing plate of claim 10.