TW201710718A - Method for producing polarizer - Google Patents

Abstract

This invention relates to a method for producing a polarizer, specifically, in the producing steps of performing dry-elongation, stress relaxation, dyeing and crosslinking for a film for forming polarizer, the dry-elongation step being performed with a crystalline rate of the film being 0.6 to 0.8, thereby not causing the break of film during dyeing or crosslinking step even using a thin film, and thus capable of improving producibility of polarizer and capable of producing a polarizer having excellent optical properties.

Description

Polarizer manufacturing method

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 a polarizer having a polyvinyl alcohol (PVA) film in which an iodine compound or a dichroic polarizing material is adsorbed and aligned, and has a polarizer protective film on one area of the polarizer, and is polarized. The other side of the sheet is sequentially laminated with a polarizer protective film, an adhesive layer bonded to the liquid crystal cell, and a multilayer structure of the release film.

The polarizer constituting the polarizing plate is suitable for an image display device, and is required to provide a high transmittance and a degree of polarization in order to provide an image excellent in color reproducibility. In order to achieve this, a polarizer is produced by modifying the polyvinyl alcohol film itself or by using a non-sublimation dichroic dye in place of the sublimation iodine-based polarizing element.

In such a case, the film can be specifically made to have a high transmittance by using a polyvinyl alcohol-based film, but because of the film, the film is easily broken in the manufacturing step (particularly, the dyeing or crosslinking step), and there is a degree of polarization, etc. Optics Significantly reduced performance.

Korean Laid-Open Patent Publication No. 10-2009-0070085 discloses a method of manufacturing a polarizer, but does not suggest an alternative to the above problems.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Korean Patent Publication No. 10-2009-0070085

It is an object of the present invention to provide a polarizing film which is excellent in optical characteristics and which can reduce the breakage of the film for forming a polarizer in the production step and improve the productivity.

A method for producing a polarizer comprising the steps of dry stretching, stress relaxation, dyeing, and crosslinking of a film for forming a polarizer; and the dry stretching step is performed in such a manner that the degree of crystallization of the film satisfies 0.6 to 0.8. .

2. The method of producing a polarizer according to the above 1, wherein the film has a degree of crystallization of from 0.61 to 0.75.

3. The method of producing a polarizer according to the above 1, wherein the film for forming a polarizer has a thickness of 10 to 30 μm.

4. The method of producing a polarizer according to the above 1, wherein the film of the dry stretching step has an elongation ratio of 4 to 5 times.

5. The method for producing a polarizer according to 1, wherein The aforementioned dry stretching step is carried out at 120 to 140 °C.

6. The method for producing a polarizer according to the above 1, wherein the stress relaxation step is performed by immersing in an aqueous solution for stress relaxation at 20 to 50 °C.

7. The method of producing a polarizer according to the above 1, wherein the stress relieving step is performed for 40 to 180 seconds.

8. The method of producing a polarizer according to the above 1, wherein the film of the stress relaxation step has an elongation ratio of 0.9 to 1 time.

9. The method for producing a polarizer according to the above 1, wherein the dyeing step is carried out by immersing in an aqueous solution for dyeing at 5 to 42 °C.

10. The method of producing a polarizer according to the above 1, wherein the dyeing step is performed for 60 to 200 seconds.

11. The method of producing a polarizer according to the above 1, wherein the film of the dyeing step has an elongation ratio of from 1 to 1.1 times.

12. The method for producing a polarizer according to the above 1, wherein the crosslinking step is carried out by immersing in an aqueous solution for crosslinking at 20 to 90 °C.

13. The method of producing a polarizer according to the above 1, wherein the crosslinking step is performed for 1 second to 15 minutes.

14. The method of producing a polarizer according to the above 1, wherein the film of the crosslinking step has an elongation ratio of 0.99 to 1.65 times.

15. The method of producing a polarizer according to the above 1, wherein the step of crosslinking further comprises a step of washing and drying.

The method for producing a polarizer of the present invention is to perform a dry stretching step before entering the wet step, wherein the degree of crystallization of the film is within a specific range in the dry step, whereby the film is not broken during the manufacturing step. Excellent sex.

The method for producing a polarizer of the present invention can produce a polarizer excellent in optical characteristics.

The present invention relates to a method for producing a polarizer, and more particularly to a method for manufacturing a film for forming a polarizer by a step of dry stretching, stress relaxation, dyeing, and crosslinking, The dry stretching step is carried out in such a manner that the degree of crystallization of the film satisfies 0.6 to 0.8, whereby even if a film of the film is used, film breakage does not occur in the dyeing or crosslinking step, so that the productivity of the polarizer can be improved, and A method of producing a polarizer having excellent optical characteristics.

The polarizer is manufactured by specifically realizing the optical characteristics required for the display to be applied, appropriately adjusting the material of the film for forming a polarizer, the step conditions, etc., but when used in a polarizer of an OLED, it is sometimes required to have high penetration. The polarizer of the rate. In order to manufacture such a polarizing plate having a high transmittance, a film for forming a polarizer for a film is used. However, at this time, in the manufacturing step (particularly, a dyeing or crosslinking step), the film is easily broken, and there is a degree of polarization or the like. The problem of significantly reduced optical properties.

Therefore, the present invention performs a dry stretching step before entering the wet step, and produces a film having a proper degree of crystallization through a dry stretching step, whereby even if a film of the film is used, a polarizer which does not cause the aforementioned problem can be derived. Production method.

The method for producing a polarizer of the present invention is a step of subjecting the film for forming a polarizer to dry stretching, stress relaxation, dyeing, and crosslinking.

Hereinafter, an embodiment of the present invention will be described in more detail.

<dry extension step>

The method for producing a polarizer of the present invention is a step of dry-extending a film for forming a polarizer before entering the wet step.

By the above-described dry stretching step, the film is extended in such a manner that the degree of crystallization becomes 0.6 to 0.8, whereby the strength of the film is improved, and even if it is formed into a film, a wet step (in particular, a dyeing and crosslinking step) which will be described later can be used. The incidence of breakage of the film is reduced, thereby improving the productivity of the polarizer. Further, at the end of the dry stretching step, when the degree of crystallization of the film satisfies the range of the degree of crystallization, the degree of polarization is not easily lowered.

The "degree of crystallization" in the present invention is a ratio of the crystallinity of the crystal portion and the non-crystal portion of the polymer constituting the film to the film for polarizer formation in the dry stretching step. It can be determined by methods generally known in the art.

In the dry stretching step of the present invention, when the degree of crystallization of the film at the end of the dry stretching is less than 0.6, the dyeing and crosslinking step described later is liable to be broken, and the degree of crystallization of the film at the end of the dry stretching exceeds 0.8. At the time, the optical characteristics, especially the degree of polarization, are lowered. Further, the degree of crystallization of the film is preferably from 0.61 to 0.75, and in this case, more excellent optical characteristics can be realized by the absence of the above problems.

The degree of crystallization can be specifically achieved by a known method in the field. For example, when the stretching ratio is increased in the MD direction, the degree of crystallization after stretching tends to be high, so that the crystallization can be controlled by the adjustment of the stretching ratio. Further, it can be specifically achieved by adjusting the temperature of the film, the material of the film for forming a polarizer, the type and content of the additive (plasticizer, etc.), and the moisture content of the film to an appropriate range. Limited to this.

The film for forming a polarizer of the present invention can easily carry out the dry stretching step of the present invention, and can be dyed by a dichroic substance, that is, iodine or the like, and the type thereof is not particularly limited, for example, a polyvinyl alcohol film. , partially saponified polyvinyl alcohol film; polyethylene terephthalate film, ethylene-vinyl acetate copolymer film, ethylene-vinyl alcohol copolymer film, cellulose film, hydrophilicity of these partially saponified films, etc. A polymer film; a dehydration-treated polyvinyl alcohol film, a polyene alignment film such as a polyvinyl alcohol-based film subjected to dehydrochlorination treatment, or the like. Among these, not only the effect of enhancing the uniformity of the degree of polarization in the plane is excellent, but also the point of excellent dyeing affinity for iodine is preferably a polyvinyl alcohol film.

The thickness of the film for forming a polarizer is not particularly limited, and may be, for example, 10 to 30 μm. When the above range is satisfied, an excellent transmittance can be specifically achieved, and sufficient strength can be ensured by the manufacturing steps of the present invention, which will be described later. The wet step does not cause breakage of the film, so it is suitable.

In the dry extension step of the present invention, the elongation ratio of the film is It is not particularly limited and may be about 4 to 5 times, preferably 4.0 to 4.8 times. When the above range is satisfied, it is suitable to specifically achieve the above-mentioned appropriate degree of crystallization, and when it exceeds about 5 times, the dyeing property of iodine is lowered in the dyeing step to achieve desired optical characteristics.

The temperature at which the dry stretching step of the present invention is carried out is not particularly limited, and is, for example, 120 to 140 ° C, preferably 125 to 135 ° C. When the above range is satisfied, it is suitable to achieve the above-mentioned appropriate degree of crystallization. When the temperature exceeds 140 ° C, the degree of crystallization is too high, and in the dyeing step, the dyeability of iodine is lowered, and it is difficult to specifically achieve the desired optical characteristics.

The execution time of the dry stretching step of the present invention is not particularly limited, and may be appropriately carried out within the range of the appropriate degree of crystallization obtained, for example, from 1 second to 1 minute, preferably from 5 to 30 seconds.

The method for carrying out the dry stretching step of the present invention is not particularly limited, and examples thereof include a method of applying a tension to a film and rolling by a pressure roller, a method of imparting tension to the film to contact the heating roll, and an inside or outside of the heating oven. The method of heating the film between the rolls and applying the tensile force while performing the stretching; the method of compressing and extending between the two heating rolls, etc., at this time, the implementation temperature of the dry stretching step can be adjusted by It is realized by extending the temperature of the roller and the oven.

In the method for producing a polarizer of the present invention, the extension of the film for forming a polarizer can be carried out simultaneously with a wet step (stress relaxation, dyeing, crosslinking step, etc.) to be described later, in addition to the dry stretching step.

<stress relaxation step>

The manufacturing steps of the polarizer of the present invention are carried out after dry extension Force to ease the steps.

In the stress relaxation step, the film for forming a polarizer after dry stretching is immersed in a stress relaxation groove filled with an aqueous solution for stress relaxation before the dyeing step, and impurities such as dust or an anti-caking agent deposited on the surface of the film are removed, and the polarizer is alleviated. The step of forming the stress of the film, improving the dyeability, preventing the dyeing unevenness, and improving the physical properties of the polarizer.

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

When glycerin and potassium iodide are contained, the content thereof is not particularly limited. For example, the total weight of the aqueous solution for stress relaxation is 5% by weight or less, and may be 10% by weight or less.

The temperature at which the stress relaxation step is carried out (the temperature of the aqueous solution for stress relaxation) is not particularly limited, and is, for example, 20 to 50 ° C, preferably 25 to 40 ° C. When the temperature of the stress relaxation step is within the above range, stress relaxation is appropriately performed, and the occurrence of cracking of the film can be remarkably reduced.

The implementation time of the stress relaxation step (stress relaxation tank immersion time) is not particularly limited, and may be, for example, 40 seconds to 180 seconds or less, preferably 90 seconds or shorter. When the execution time of the stress relaxation step is within the above range, when the temperature of the stress relaxation step is within the above range, stress relaxation is appropriately performed, and the occurrence of film breakage can be remarkably reduced.

The stress relaxation step and the wet extension step may be simultaneously performed. In this case, the elongation ratio of the stress relaxation step may be about 0.9 to 1 times, and within the above range, the appropriate range may be performed without reducing the optical characteristics. The stress is relieved.

<staining step>

The method for producing a polarizer of the present invention is followed by the dyeing step after the stress relaxation step.

In the dyeing step, the film for forming a polarizer is immersed in a dyeing tank containing a dichroic substance such as an aqueous solution containing iodine, and the film for forming a polarizer is adsorbed with iodine.

The aqueous solution for dyeing may contain water, a water-soluble organic solvent or a mixed solvent of these and iodine.

The concentration of iodine in the aqueous solution for dyeing may be from 0.4 to 400 mmol/L, preferably from 0.8 to 275 mmol/L, more preferably from 1 to 200 mmol/L, in the dyeing solution.

Further, the aqueous solution for dyeing may further contain an iodide as a co-solvent in order to improve the dyeing efficiency.

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 at a point where the solubility to water is large. 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 the total weight of the aqueous solution for dyeing.

Further, the aqueous solution for dyeing may further contain boric acid in order to increase the content of the iodine complex of the film for forming a polarizer.

The content of the above boric acid is not particularly limited, and may be, for example, 0.3 to 5% by weight based on the total weight of the aqueous solution for dyeing. When the above range is satisfied, it is preferable to increase the content of the PVA-I ₃ ^- complex and the PVA-I ₅ ^- complex, but when it exceeds 5% by weight, the risk of breakage of the film increases.

The execution temperature of the dyeing step (the temperature of the aqueous solution for dyeing) is not particularly limited and may be, for example, 5 to 42 ° C, preferably 10 to 35 ° C. When the temperature of the dyeing step is within the above range, the film is not broken, and iodine is efficiently adsorbed on the film to realize excellent optical characteristics.

The implementation time of the dyeing step (dye bath immersion time) is not particularly limited and may be, for example, 60 to 200 seconds, and preferably 80 to 150 seconds. When the time of the dyeing step is within the above range, the film is not broken, and iodine is efficiently adsorbed on the film to realize excellent optical characteristics.

The dyeing step and the wet stretching step may be simultaneously performed, and in this case, the stretching ratio of the dyeing step may be about 1 to 1.1 times, and within the above range, excellent optical characteristics can be specifically achieved without breaking the film.

Further, the cumulative stretching ratio in the stress relaxation step and the dyeing step is preferably 0.9 to 1.1 times, and when the cumulative stretching ratio is less than 0.9 times, wrinkles are formed on the film to cause a poor appearance, and when it exceeds 1.1 times There will be situations in which the extension is uneven.

<Crosslinking step>

The method for producing a polarizer of the present invention is followed by the step of dyeing, followed by a crosslinking step.

The crosslinking step is such that the dyeing property caused by the physically adsorbed iodine molecules is lowered by the external environment, and the dyed polarizer is formed. The step of immersing the membrane in an aqueous solution for crosslinking to crosslink and immobilizing the adsorbed iodine molecules. When the iodine crosslinking reaction of the dichroic dye is insufficient, the iodine molecule may be detached due to the moist heat environment, and a sufficient crosslinking reaction is required. Further, since the film for forming a polarizer is used to align the iodine molecules located between the molecules and the molecules to enhance the optical characteristics, it is preferable to extend the cross-linking step with a large extension ratio.

Therefore, the crosslinking step can be carried out by the first crosslinking step and the second crosslinking step. In at least one step of the above step, an aqueous solution for crosslinking containing a boron compound can be used. The above boron compound improves the optical characteristics of the polarizer while improving the color durability.

The aqueous solution for crosslinking may contain water and a boron compound, and may further contain an organic solvent and an iodide which can interact with water.

The boron compound imparts rigidity to the short cross-linking bond and the film, and suppresses wrinkles of the film in the step, thereby improving handleability and exhibiting an action of forming an iodine alignment.

The concentration of the boron compound in the aqueous solution for cross-linking is not particularly limited, and may be, for example, 1 to 10% by weight based on the total weight of the aqueous solution for crosslinking. When the above range is satisfied, the crosslinking is carried out in an appropriate range, and the specificity can be specifically achieved. Optical properties. On the other hand, when it is less than 1% by weight, the crosslinking effect is lowered to lower the rigidity of the film, and when it exceeds 10% by weight, the film may be broken due to excessive crosslinking bonds.

Further, the aqueous solution for crosslinking may further contain an iodide in order to prevent the uniformity of the degree of polarization in the surface of the polarizer and prevent the iodine from being detached.

The content of the iodide in the aqueous solution for cross-linking is not particularly limited. For example, the total weight of the aqueous solution for crosslinking may be 0.05 to 15% by weight, preferably 0.5 to 11% by weight. When the above range is satisfied, it is possible to prevent the iodide ions adsorbed in the dyeing step from coming out of the film, or the iodide ions contained in the cross-linking liquid from penetrating into the film, thereby suppressing the change in the transmittance.

The temperature at which the crosslinking step is carried out (the temperature of the aqueous solution for crosslinking) is not particularly limited, and may be, for example, 20 to 90 ° C, preferably 50 to 75 ° C, and when the temperature of the crosslinking step is within the above range, the film By arranging iodine in an appropriate range without breaking, excellent optical characteristics can be specifically achieved.

The implementation time of the crosslinking step (cross-linking tank immersion time) is not particularly limited and may be, for example, 1 second to 15 minutes, preferably 5 seconds to 10 minutes. When the time of the crosslinking step is within the above range, the film is aligned in an appropriate range without breaking, and excellent optical characteristics can be specifically achieved.

The crosslinking step and the wet stretching step may be simultaneously performed. In this case, the stretching ratio of the crosslinking step may be about 0.99 to 1.65 times. Within the above range, the film may be aligned without rupture and the iodine may be in an appropriate range. Achieve excellent optical properties, thereby improving the productivity of polarizers.

Further, when the crosslinking step is carried out by the first crosslinking step and the second crosslinking step, the stretching ratio of the first crosslinking step may be about 1.1 to 1.5 times, and the stretching ratio of the second crosslinking step may be about 1 to 1.3 times, the cumulative elongation ratio of the first crosslinking step and the second crosslinking step may be about 0.99 to 1.65 times.

<Washing step>

The method for producing a polarizer of the present invention is completed at the end of the crosslinking step as needed Thereafter, a water washing step may be further included.

The water washing step is a step of immersing the film for forming a polarizer which is extended and crosslinked in a water washing tank filled with the aqueous solution for washing, and removing the unnecessary residue adhering to the film for polarizer formation in the previous step.

The aqueous solution for washing may be water (deionized water), and iodide may be further added thereto.

The execution temperature of the water washing step (the temperature of the aqueous solution for washing) is not particularly limited and may be, for example, 0 to 60 ° C, preferably 5 to 30 ° C.

The water washing step may be omitted, or may be performed at the end of the steps such as the stress relieving step, the dyeing step, and the cross-linking step. Further, the number of repetitions 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 film for forming a water-repellent polarizer, and further improving the alignment of the iodine molecules which are internally densified by drying, thereby obtaining a polarizer having excellent optical characteristics.

The drying method is not particularly limited, and methods such as natural drying, air drying, heat drying, far infrared ray drying, microwave drying, hot air drying, and the like can be used. Recently, microwave treatment in which only water in the film is activated and dried can be used. Usually, hot air treatment and far infrared treatment are mainly used.

The temperature at which the hot air is dried is not particularly limited. In order to prevent deterioration of the polarizer, it is preferably carried out at a relatively low temperature, and may be, for example, 20 to 105 ° C, preferably 100 ° C or lower.

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

The method for producing a polarizer of the present invention may be carried out by immersing a film for forming a polarizer in a constant-temperature water tank, except for the dry stretching step and the drying step in the above steps.

In the polarizer for the method for producing a polarizer, the polarizer can be used in the production of a polarizing plate having a protective film on at least one area.

The type of the protective film is not particularly limited as long as it is excellent in transparency, mechanical strength, thermal stability, water barrier properties, and isotropic properties, and specific examples thereof include polyparaphenylene. a polyester resin such as ethylene formate, polyethylene isophthalate or polybutylene terephthalate; a cellulose resin such as diethyl cellulose or triacetyl cellulose; and polycarbonate Resin; polyacrylic resin such as poly(methyl) acrylate or poly(methyl) acrylate; styrene resin such as polystyrene or acrylonitrile-styrene copolymer; polyethylene, polypropylene a polyolefin resin having a ring-like or norbornene structure, a polyolefin-based resin such as an ethylene-propylene copolymer, a polyamine-based resin such as nylon or an aromatic polyamine; a quinone imine resin; and a polyether fluorene-based resin Resin; lanthanide resin; polyether ketone resin; polyphenylene sulfide resin; vinyl alcohol resin; vinylidene chloride resin; vinyl butyral resin; aromatic acid ester resin; polyoxymethylene resin; A film made of a thermoplastic resin such as an oxygen resin may be used before Composed of a blend of a thermoplastic resin film. Further, a thermosetting resin such as a (meth)acrylic acid, an urethane-based, an epoxy-based or an anthracene-based resin, or an ultraviolet-curable resin may be used. The film into a film. Among these, in consideration of polarizing characteristics or durability, a cellulose film having a surface which is saponified with a base or the like is particularly preferable. Further, the protective film may be a function of the optical layer described below.

The structure of the polarizing plate is not particularly limited, and various types of optical layers satisfying necessary optical characteristics may be laminated on the polarizer. For example, a structure of a protective film for protecting a polarizer is provided on at least one area of the polarizer; a hard coat layer, an anti-reflection layer, an anti-adhesion layer, an anti-diffusion layer, and an anti-glare layer are laminated on at least one side of the polarizer or the protective film. The structure of the surface treatment layer; or an alignment liquid crystal layer having a compensation viewing angle on at least one side of the polarizer or a protective film, or a structure in which other functional films are laminated. Further, a wavelength plate (including a λ plate) such as an optical film, a reflection sheet, a semi-transmissive plate, a 1⁄2 wavelength plate, or a 1⁄4 wavelength plate used for forming various types of image display devices, such as a polarization conversion device, is used. One or more of the phase difference plate, the viewing angle compensation film, and the brightness enhancement film are laminated as an optical layer. More specifically, a polarizing plate having a structure of a protective film on one of the polarizing plates, a reflective polarizing plate or a semi-transmissive polarizing plate in which a reflecting sheet or a semi-transmissive reflecting sheet is laminated on the protective film of the laminated layer. A plate; an elliptical or circular polarizing plate having a phase difference plate; a wide viewing angle polarizing plate having a viewing angle compensation layer or a viewing angle compensation film; or a polarizing plate having a brightness enhancing film laminated thereon.

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 organic electric field light-emitting display device (OLED), a plasma display device, and an electric field emission display device.

In the following, preferred embodiments are suggested to facilitate the understanding of the present invention, but such embodiments are merely illustrative of the present invention and are not limiting. The scope of the invention and the scope of the technical scope of the invention can be variously changed and modified by those skilled in the art to which the invention pertains, and such modifications and corrections are The scope of the patent application is attached.

Examples and comparative examples

(Example 1)

A transparent unstretched polyvinyl alcohol film (PE30, KURARAY Co., Ltd.) having a thickness of 30 μm and a degree of saponification of 99.9% or more was subjected to a 4-fold dry stretching by a hot roll at 120 °C. The degree of crystallization of the film was measured after stretching.

Thereafter, the dry-extending film was immersed in water (deionized water) at 25 ° C for 1 minute and 20 seconds to relax the stress, and then contained 1.25 mM/L of iodine, 1.25 % by weight of potassium iodide, and 0.3% by weight of boric acid. The dyeing at °C was immersed in an aqueous solution for 2 minutes for dyeing. At this time, the stress relaxation and the dyeing step were extended at an elongation ratio of 0.92 times and 1.002 times, respectively, and the cumulative elongation ratio from the stress relaxation groove to the dyeing groove was 0.922. Then, it was immersed in a crosslinking liquid containing 10% by weight of potassium iodide and 8% by weight of boric acid at 65 ° C for 30 seconds (first crosslinking step) to be crosslinked, and extended at a stretching ratio of 1.3 times. Thereafter, the mixture was immersed in a crosslinking liquid containing 10% by weight of potassium iodide and 8% by weight of boric acid at 65 ° C for 20 seconds (second crosslinking step) to be crosslinked and extended at an extension ratio of 1.03 times.

At this time, the total cumulative elongation ratio of the stress relaxation, dyeing, and crosslinking steps was 1.234 times. After the completion of the crosslinking, the polyvinyl alcohol film was dried in an oven at 100 ° C for 1 minute to prepare a polarizer, and the transmittance of the produced polarizer was 43.5%.

Hereinafter, samples were prepared so that the transmittances of all of Examples 1 to 10 and Comparative Examples 1 to 7 were within a range of 43.5% (deviation 0.2%).

(Examples 2 to 7 and Comparative Examples 1 to 4)

A polarizer was produced in the same manner as in Example 1 except that the dry stretching ratio and the dry stretching temperature described in Table 1 below were adjusted.

(Comparative Example 5)

A polarizer was produced in the same manner as in Example 1 except that dry stretching was not carried out.

(Example 8)

A polarizer was produced in the same manner as in Example 1 except that the thickness of the polyvinyl alcohol film was 20 μm.

(Example 9)

A polarizer was produced in the same manner as in Example 1 except that the stress relaxation was performed by immersing in water for 1 minute and 30 seconds.

(Embodiment 10)

A polarizer was produced in the same manner as in Example 1 except that the stress was alleviated by immersion in water at 40 °C.

(Example 11)

A polarizer was produced in the same manner as in Example 1 except that the stress relaxation was performed by immersing in water at 40 ° C for 1 minute and 30 seconds.

(Comparative Example 6)

A polarizer was produced in the same manner as in Comparative Example 1, except that the thickness of the polyvinyl alcohol film was 60 μm.

<The degree of crystallization of the film after dry stretching>

Measurement of absorbance: After the dry stretching, the polyvinyl alcohol film is cut into 10*10 mm or more after the width and length, and the infrared spectroscopic spectrum of the ATR-IR method (Attenuated Total Reflection Infrared Spectroscopy) is used. Fourier transform infrared spectrophotometry (Infrared spectrophotometer manufactured by Thermo Fisher Scientific Co., Ltd.: NICOLET 5700, ATR unit manufactured by Pike Technology Co., Ltd.: VeeMAX III), and the absorbance was measured under the following conditions.

Number of scans: 16 times

Final format: Absorbance mode

Measuring angle: 45 degrees

Wave number resolution: 4cm ^-1

Measuring wave number range: 400 to 4000 cm ^-1

Scanning speed: 9.6kHz

Low pass filter: automatic

Light source: IR (ceramic)

Beamsplitter: KBr

Detector: DTGS KBr

Crystallization: ZnSe

Measurement direction: measured in such a manner that the incident direction of light is parallel to the absorption axis direction of the polarizer

The degree of crystallization was determined using the following formula. (C = degree of crystallization)

In the formula, A ₁₁₄₃ , A ₁₀₉₃ and A ₂₀₀₀ are absorbances in wave numbers ₁₁₄₃ , ₁₀₉₃ and ₂₀₀₀ cm ^-1 , respectively.

<Feature evaluation of polarizer>

The physical properties of the polarizer produced in the above examples and comparative examples are The results were measured by the following methods, and the results are shown in Table 2 below.

1. Optical properties (polarity, penetration)

After the produced polarizer was broken 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).

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

(In the formula, T ₁ is a parallel transmittance obtained when a pair of polarizers are arranged in a state in which absorption axes are parallel, and T ₂ is an orthogonal penetration obtained when a pair of polarizers are arranged in a state in which absorption axes are orthogonal to each other. rate).

2. Fracture evaluation

The occurrence/absence of breakage when the polarizer was produced under the conditions of the examples and the comparative examples was visually confirmed based on the following evaluation criteria.

<Evaluation criteria>

○: No film breakage or cracking occurred at all

△: Breakage or cracking of the film below 2 times occurred

×: Cracking or cracking of the film more than 3 times occurred

As is apparent from the above Table 2, the polarizer produced by the production method of the present invention exhibited excellent optical characteristics and did not break during the production steps.

After the dry stretching step, in the case of Comparative Examples 1 to 4 and 6 in which the degree of crystallization exceeded the range of the present invention, it was confirmed that the film was broken or a large number of fine cracks occurred in the step, and the degree of crystallization exceeded the present invention. In the case of Comparative Examples 2, 3 and 6, in the limited range, it was confirmed that the optical characteristics were remarkably lowered.

In particular, in the case of Comparative Example 5 in which the dry stretching step was not carried out at all, it was confirmed that cracking often occurred in the production step.

Further, in the case of Example 8, when compared with Comparative Example 6, the case of Example 8 was such that no fracture occurred when a film of a film of 20 μm was used, but Comparative Example 8 having a degree of crystallization exceeding the range of the present invention was 60 μm. It was confirmed that the film was broken twice or less on the film.

Claims (15)

A method for producing a polarizer comprises the steps of dry stretching, stress relaxation, dyeing, and crosslinking of a film for forming a polarizer; and the dry stretching step is performed such that the degree of crystallization of the film satisfies 0.6 to 0.8. The method for producing a polarizer according to claim 1, wherein the film has a degree of crystallization of from 0.61 to 0.75. The method for producing a polarizer according to the first or second aspect of the invention, wherein the film for forming a polarizer has a thickness of 10 to 30 μm. The method for producing a polarizer according to any one of claims 1 to 3, wherein the film of the dry stretching step has an elongation ratio of 4 to 5 times. The method for producing a polarizer according to any one of claims 1 to 4, wherein the dry stretching step is carried out at 120 to 140 °C. The method for producing a polarizer according to any one of claims 1 to 5, wherein the stress relaxation step is carried out by immersing in an aqueous solution for stress relaxation at 20 to 50 °C. The method for producing a polarizer according to any one of claims 1 to 6, wherein the stress relieving step is performed for 40 to 180 seconds. The method for producing a polarizer according to any one of claims 1 to 7, wherein the film of the stress relaxation step has an elongation ratio of 0.9 to 1 time. The method for producing a polarizer according to any one of claims 1 to 8, wherein the dyeing step is carried out by immersing in an aqueous solution for dyeing at 5 to 42 °C. The method for producing a polarizer according to any one of claims 1 to 9, wherein the dyeing step is carried out for 60 to 200 seconds. The method for producing a polarizer according to any one of claims 1 to 10, wherein the film of the dyeing step has an elongation ratio of 1 to 1.1 times. The method for producing a polarizer according to any one of claims 1 to 11, wherein the crosslinking step is carried out by immersing in an aqueous solution for crosslinking at 20 to 90 °C. The method for producing a polarizer according to any one of claims 1 to 12, wherein the crosslinking step is performed for 1 second to 15 minutes. The method for producing a polarizer according to any one of claims 1 to 13, wherein the film of the crosslinking step has an elongation ratio of 0.99 to 1.65 times. The method for producing a polarizer according to any one of claims 1 to 14, wherein after the crosslinking step, a water washing and drying step is further included.