TW201707942A - Method for producing polarizer - Google Patents

Abstract

This invention relates to a method for producing a polarizer, specifically, the method containing the steps of performing dry-elongation, stress relaxation, dyeing and crosslinking for a film for forming polarizer, so as to produce a polarizer with a rate of crosslinking of boric acid of 4.0 to 5.5, thereby capable of producing a polarizer not bringing inclined uneven and 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-based compound or a dichroic polarizing material is adsorbed and oriented, and has a polarizer protective film on one of the polarizers, 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 have both high transmittance and polarization degree 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.

On the other hand, in general, shrinkage of the polarizer is produced in the manufacturing step of the polarizer, but unevenness in the concentration of the complex of the dichroic dye is generated in the contracted portion, and the polarizer produced is placed at a high temperature. article In the case of the above, the above-mentioned complex compound is uneven in the portion where unevenness is formed, and there is a problem that the optical characteristics are remarkably lowered. The polarizers produced are used in articles and placed in a variety of environmental conditions and must be useful in solving such problems.

Korean Laid-Open Patent Publication No. 10-2009-0070085 discloses a method of manufacturing a polarizer, but an alternative to the above problem cannot be proposed.

[Previous Technical Literature] [Patent Literature]

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

An object of the present invention is to provide a method for producing a polarizer which is capable of producing a polarizer which does not cause an oblique unevenness in accordance with a direction of an axial angle after being exposed to a high temperature environment in the formation of a laminated polarizer and a retardation film. .

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 boronic acid cross-linking efficiency represented by the formula (1) of the polarizer produced is 4.0. To 5.5; boric acid crosslinking efficiency = (degree of crosslinking of polarizer (%) × 10.81) / (boron content (%) × 3) (1) (wherein, the degree of crosslinking of the polarizer is (2) As shown, the boron content is the weight fraction (%) of boron contained in the polarizer; the degree of crosslinking (%) of the polarizer = (the absorbance integral value of the polarizer of 1200 to 1360 cm ^-1 / 2850 of the polarizer) The absorbance integral value of 3000cm ^-1 ) × 100...(2)

2. In the method for producing a polarizer according to the above 1, after the dry stretching step, the film has a shrinkage ratio in the TD direction of 25 to 40% before and after the wet step including stress relaxation, dyeing, and crosslinking.

3. In the method of producing a polarizer according to the above 1, the film for forming a polarizer has a thickness of 20 to 80 μm.

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

5. In the method of producing a polarizer according to the above 1, the dry stretching step is carried out at 120 to 140 °C.

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

7. In the method of producing a polarizer according to the above 1, the stress relieving step is carried out for 40 to 180 seconds.

8. In the method of producing a polarizer according to the above 1, the film extension ratio of the stress relaxation step is 0.9 to 1 time.

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

10. In the method of producing a polarizer according to the above 1, the dyeing step is carried out for 60 to 200 seconds.

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

12. In the method for producing a polarizer according to the above 1, 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 of the present invention is to perform a dry stretching step before entering the wet step, and to perform a dry step and a wet step in an appropriate range to produce a polarizer that satisfies a specific range of boric acid crosslinking efficiency, and is exposed to After the high-temperature environment, the polarizer is less likely to be uneven in orientation, and a polarizer having excellent optical characteristics can be produced.

The present invention relates to a method for producing a polarizer, and more particularly, to a step of dry stretching, stress relaxation, dyeing, and crosslinking of a film for forming a polarizer, wherein the cross-linking efficiency of boric acid of the polarizer becomes 4.0 to 5.5. By manufacturing in such a manner, the polarizer is less likely to be unevenly inclined after being exposed to a high temperature environment, and a polarizer excellent in optical characteristics can be produced.

In general, when a polarizer is produced, shrinkage occurs in the TD (wide) direction, but the formation of the iodine complex is made non-uniform by such shrinkage, resulting in unevenness in surface roughness. When the polarizer thus produced is placed in a high temperature condition, color unevenness is generated by decomposition of the iodine complex, and such color unevenness is generated in accordance with the axial angle of the laminated film. The problem of "inclined unevenness" in the direction of viewing.

Therefore, in the case of producing a polarizer, the present invention performs a step of dry-extending the film for forming a polarizer before entering the wet step, and performs each step condition in an appropriate range, thereby producing a boric acid crosslinking efficiency of 4.0 to The polarizer of 5.5 significantly reduces the occurrence of oblique unevenness and significantly improves the optical characteristics of the polarizer.

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

The method for producing a polarizer of the present invention is carried out by a method of dry stretching, stress relaxation, dyeing, and crosslinking, so that the boronic acid crosslinking efficiency of the polarizer satisfies 4.0 to 5.5.

In the present invention, the "boric acid cross-linking efficiency" means the efficiency of the cross-linking, the cross-linking of the polyvinyl alcohol resin and the boric acid, the cross-linking of the two cross-linking bonds, and the cross-linking of the three cross-linking bonds. The ratio of the content of the boric acid compound to the degree of crosslinking with respect to the produced polarizer can be specifically defined by the following formula (1).

Boric acid crosslinking efficiency = (degree of crosslinking of polarizer (%) × 10.81) / (boron content (%) × 3) (1)

In the formula, the degree of crosslinking means the ratio of the cross-linking bonds of polyvinyl alcohol to boric acid, and the ratio of the area at the start of crosslinking and the area of the infrared spectrum data at the end of the cross-linking is determined in advance. Formula (2) definition.

Crosslinking the polarizer degree (%) = (polarizer 1200 to 1360cm ^-1 of an integrated value of absorbance / 2850 3000cm ^-1 to an integrated value of absorbance of the polarizer) × 100 ... (2)

With respect to the above formula (2), the absorbance integral value of 1200 to 1360 cm ^-1 means the area of the peak of the cross ^- linking bond of the polyvinyl alcohol and the boric acid compound, and the absorbance integral value of 2850 to 3000 cm ^-1 means polyethylene. The area of the peak of the carbon single bond of the alcohol can be determined by a usual method in the field.

Further, the boron content means the weight fraction (%) of boron contained in the polarizer.

In the present invention, when the cross-linking efficiency of the boric acid of the polarizer is satisfied to satisfy the above range, the TD (wide) direction shrinkage ratio in the wet step can be satisfied in an appropriate range, and the oblique direction can be suppressed after exposure to a high temperature environment. Not uniform, so it is better.

The above-mentioned polarizer may have a boric acid crosslinking efficiency of from 4.3 to 5.2, and the above effects can be further improved within the above range.

The boron content may be 3% or more and 6% or less, may be 4% or more and 5% or less, or may be 4.5% or more and 4.9% or less. By adjusting the boron content to the above range, it is possible to suppress a decrease in optical characteristics after exposure to a high temperature environment, and it is also possible to suppress occurrence of unevenness.

The boric acid crosslinking efficiency of the present invention can be specifically achieved by adjusting the manufacturing step conditions of the polarizer to an appropriate range, in particular, by extending the stretching ratio of the dry stretching step and the step temperature, the temperature of the stress relieving groove, The content of boric acid, the elongation ratio, the step temperature, and the like in the crosslinking step are adjusted to an appropriate range to be specifically achieved. In particular, when the stretching ratio and the temperature conditions are adjusted under the wet step, it is easy to satisfy the boric acid crosslinking efficiency within the range of the present invention.

In the present invention, the boric acid compound contains boric acid and boron. All of sodium and the like.

Further, the method for producing a polarizer of the present invention is carried out in such a manner that the shrinkage ratio in the TD direction satisfies 25 to 40% in the wet step after the dry stretching step.

In the present invention, the TD-direction shrinkage ratio means the rate of change in the width direction of the polarizer before and after the wet step, and in the present invention, the wet step includes stress relaxation, dyeing, and crosslinking after the dry stretching step. The steps are all.

In the present invention, after the dry stretching step, when the shrinkage ratio of the polarizer in the TD direction satisfies the range of 25 to 40%, the iodine complex is uniformly formed in the entire polarizer, and the color can be reduced after exposure to a high temperature environment. The unevenness, whereby a polarizer having a boric acid crosslinking efficiency in the above range can be produced.

The shrinkage ratio in the TD direction is preferably 28 to 35%, and the unevenness of the thickness of the polarizer is reduced within the above range, and the above effects can be further enhanced.

<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.

Through the aforementioned dry stretching step, the boric acid crosslinking efficiency of the polarizer can be adjusted to improve the strength of the film, and the wetting step (in particular, the dyeing and crosslinking step) described later reduces the incidence of film cutting, thereby improving the polarizer. Productive.

The film for forming a polarizer of the present invention can be easily carried out before The dry stretching step of the present invention may be a film dyed by a dichroic substance, that is, iodine or the like, and the kind thereof is not particularly limited, and examples thereof include a polyvinyl alcohol film, a partially saponified polyvinyl alcohol film, and polyparaphenylene. a polyethylene terephthalate film, an ethylene-vinyl acetate copolymer film, an ethylene-vinyl alcohol copolymer film, a cellulose film, a hydrophilic polymer film such as a partially saponified film, or a dehydrated polyvinyl alcohol A polyene oriented film such as a film or a polyvinyl alcohol-based film subjected to dehydrochlorination treatment. Among these, a polyvinyl alcohol-based film is preferable because it is excellent in the effect of enhancing the uniformity of the degree of polarization in the surface, and is excellent in the dyeing affinity for iodine.

The thickness of the film for forming a polarizer is not particularly limited, and is, for example, 20 to 80 μm. When the present invention is produced, in the above range, the excellent transmittance is satisfied, and the occurrence of oblique unevenness is remarkably reduced, which can be specifically realized. Excellent optical properties.

In the dry stretching step of the present invention, the film stretching ratio is not particularly limited and may be about 4 to 5 times, preferably 4.2 to 4.8 times. When the above range is satisfied, it is suitable to specifically achieve the above-described appropriate range of boric acid crosslinking efficiency, and when it exceeds about 5 times, the dyeing property of iodine is lowered in the dyeing step, and it is difficult to specifically achieve the 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 specifically achieve the boric acid crosslinking efficiency in the above-mentioned appropriate range. When the temperature exceeds 140 ° C, the dyeing property of iodine is lowered in the dyeing step, and it is difficult to specifically achieve the desired optical characteristics.

The implementation time of the dry extension step of the present invention is not particularly It is not limited, for example, it can be carried out for 1 second to 1 minute, preferably for 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 imparting tension to a film and rolling by a pressure roller, a method of applying tension to the film to contact the heating roll, and inside or outside the heating oven. The method of heating the film between the rolls and applying a tensile force while performing the stretching; the method of compressing and extending the two heating rolls, etc., at this time, the implementation temperature of the dry stretching step can be performed by It is specifically realized by adjusting the temperature of the roll and the oven for extension.

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 step of the polarizer of the present invention is followed by a stress relaxation step after dry stretching.

In the stress relaxation step, the film for forming a polarizer 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 film for forming a polarizer is relaxed. The step of improving the physical properties of the polarizer by stress, improving the dyeability and preventing the dye unevenness.

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

When it contains glycerin and potassium iodide, its content is not special. The total weight of the aqueous solution for stress relaxation is, for example, 5% by weight or less, and may be 10% by weight or less.

The execution temperature of the stress relaxation step (temperature of the aqueous solution for stress relaxation) is not particularly limited and may be, for example, 20 to 50 ° C, preferably 25 to 40 ° C. When the temperature of the stress relaxation step is within the above range, the stress relaxation is appropriately performed, and it is suitable to achieve the boric acid crosslinking efficiency in a specific range, and the film cutting can be remarkably reduced.

The implementation time of the stress relaxation step (stress relaxation tank immersion time) is not particularly limited, and is, for example, 40 seconds to 180 seconds or less, preferably 90 seconds or shorter. When the implementation time of the stress relaxation step is within the above range, the stress relaxation is appropriately performed, and it is suitable to achieve the boric acid crosslinking efficiency in a specific range, and the film cutting can be significantly reduced.

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

<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 filled with 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 be water, a water-soluble organic solvent or a mixed solvent of these and iodine.

The iodine concentration 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.

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. In the case where titanium iodide or the like has a large solubility to water, potassium iodide is preferred. These may be used alone or in combination of two or more.

The content of the iodide is not particularly limited, and is, 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 it satisfies the above range, by increasing the PVA-I ₃ ^- complexes and PVA-I ₅ ^- the content of the complexes, it is preferred, boric acid may be embodied in an appropriate range of crosslinking efficiency. However, when it exceeds 5% by weight, the risk of cutting the film is increased.

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 can be efficiently adsorbed on the film without cutting, and excellent optical characteristics can be specifically achieved.

The implementation time of the dyeing step (dye bath immersion time) is not particularly limited and may be, for example, 60 to 200 seconds, preferably 80 to 150 seconds. When the time of the dyeing step is within the above range, the iodine is efficiently adsorbed on the film without cutting, and the excellent optical characteristics can be specifically achieved.

The dyeing step and the wet stretching step can be carried out simultaneously, and in this case, the stretching step has an elongation ratio of about 1 to 1.1 times, and within the above range, the film can achieve excellent optical characteristics without cutting.

Further, the cumulative stretching ratio until 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, the film may wrinkle and the appearance may be poor, and when it exceeds 1.1 times, There will be situations where 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 by the iodine molecule which is physically adsorbed is lowered by the external environment, and the dyed polarizer forming film is immersed in an aqueous solution for crosslinking containing a boric acid compound to be crosslinked to be adsorbed. The step of immobilizing the iodine molecule. When the crosslinking reaction of iodine as a dichroic dye is insufficient, the iodine molecule may be detached due to a moist heat environment, and a sufficient crosslinking reaction is required. Further, the film for forming a polarizer is such that the iodine molecules positioned between the molecules and the molecules are oriented to enhance the optical characteristics, so that it is preferable to extend the cross-linking step with a large extension ratio.

Thus, the aforementioned crosslinking step can be carried out by the first crosslinking step And the second crosslinking step, wherein at least one step of the above step can use an aqueous solution for crosslinking containing a boric acid compound. In this case, the optical properties of the polarizer can be improved by the boric acid compound, and the color durability can be improved. Sex, so good.

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

The boric acid compound imparts rigidity to a short crosslink and a film, and suppresses wrinkles of the film in the step, thereby improving handleability and exhibiting an effect of forming an iodine orientation.

The concentration of the boric acid compound in the aqueous solution for cross-linking is not particularly limited. For example, the total weight of the aqueous solution for cross-linking may be 1 to 10% by weight. When the above range is satisfied, the cross-linking is carried out in an appropriate range, and the above-mentioned The boric acid crosslinking efficiency, whereby excellent optical characteristics can be specifically achieved. Moreover, when it is less than 1% by weight, the crosslinking effect may be reduced to lower the rigidity of the film, and when it exceeds 10% by weight, film cutting may occur due to excessive crosslinking.

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, When the appropriate range is crosslinked, the aforementioned boric acid crosslinking efficiency can be specifically achieved, whereby 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 and is crosslinked in an appropriate range, the above-described boric acid crosslinking efficiency can be specifically achieved, whereby excellent optical characteristics can be specifically achieved.

The crosslinking step and the wet stretching step can be carried out at the same time. In this case, the stretching ratio of the crosslinking step can be about 0.99 to 1.65 times. Within the above range, the iodine is oriented in an appropriate range, and the excellent optical can be realized. The characteristics, by which, can improve the productivity of the polarizer.

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 Up 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>

If necessary, the method for producing a polarizer of the present invention may further comprise a water washing step after the completion of the crosslinking step.

In the water washing step, the film for forming a polarizer which is extended and crosslinked is immersed in a washing tank filled with a water solution for washing, and the unnecessary residue adhering to the film for forming a polarizer in the preceding step is removed.

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

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 orientation 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, except for the dry stretching step and the drying step among the foregoing steps, may be All of them were carried out by immersing a film for forming a polarizer in a constant temperature water tank.

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 polyterephthalic acid. a polyester resin such as ethylene glycol ester, polyethylene isophthalate or polybutylene terephthalate; cellulose resin such as diethyl phthalocyanine or triethylene fluorene cellulose; Resin; polyacrylic resin such as poly(methyl) acrylate or poly(methyl) acrylate; styrene resin such as polystyrene or acrylonitrile-styrene copolymer; polyethylene, polypropylene, Polyolefin resin such as polyolefin or ethylene-propylene copolymer having a ring system or a norbornene structure; polyamine resin such as nylon or aromatic polyamine; quinone imine resin; polyether oxime 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 composed of a thermoplastic resin such as a resin, or the like The blend formed a plastic resin film. Further, a film made of a thermosetting resin such as a (meth)acrylic acid, an urethane-based, an epoxy-based or a fluorene-based resin, or an ultraviolet-curable resin may be used. 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 configuration of the polarizing plate is not particularly limited and may be Various types of optical layers satisfying the necessary optical characteristics are 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 directional 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 quarter-wave plate, which are used in various image display devices, such as a polarization conversion device, is formed. One or more of the retardation film, 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 polarizers; a reflective polarizing plate or a semi-transmissive polarizing plate having a reflective sheet or a semi-transmitting reflecting sheet laminated on the protective film of the laminated layer; An elliptical or circular polarizing plate in which a phase difference plate is laminated; a wide viewing angle polarizing plate in which a viewing angle compensation layer or a viewing angle compensation film is laminated; or a polarizing plate in which a brightness enhancing film is laminated is preferable.

Such a polarizing plate can be used not only in a general liquid crystal display device but also in 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, the preferred embodiments are suggested to facilitate the understanding of the present invention, but the embodiments are merely illustrative of the present invention, and are not intended to limit the scope of the appended claims, and are within the scope and technical scope of the present invention. It is to be understood by those of ordinary skill in the art that the present invention is susceptible to variations and modifications.

Examples and comparative examples

(Example 1)

A transparent unstretched polyvinyl alcohol film (PS75, KURARAY Co., Ltd.) having a thickness of 75 μm and a degree of saponification of 99.9% or more was subjected to a 4.5-fold dry stretching at 130 ° C.

Thereafter, the mixture was immersed in water (deionized water) at 40 ° C for 1 minute and 20 seconds to relax the stress, and then in an aqueous solution for dyeing containing 30.degree. C. of iodine 1.12 mM/L, 1.25 wt% of potassium iodide, and 0.3% by weight of boric acid. Dip for 2 minutes. 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 68% by weight of boric acid at 68 ° 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 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 44.5%.

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 44.5% (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 conditions described in the following Table 1 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.

<Evaluation method>

1. Boric acid 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) equipped with Thermo Fisher Scientific.

The FT-IR wafer was measured for absorbance under the following conditions using Pee technologies' VeeMAX III (ATR).

Number of scans: 16 times

Wave number resolution: 4cm ^-1

Measuring range: 400 to 4000 cm ^-1

Scanning speed: 9.6kHz

Low pass filter: automatic

Light source: IR (ceramic)

Beamsplitter: KBr

Detector: DTGS KBr

Crystallization: KBr

Angle of incidence: 45°

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

In the measured IR Data, the total area of the region of 2850 to 3000 cm ^{-1 was} used as the reference peak area (a), and the area of 1200 to 1360 cm ^-1 was divided by the reference peak area (a) to determine the degree of crosslinking.

Crosslinking degree (%) = ((area of 1200 to 1360 cm ^-1 ) / (reference peak area (a)) × 100

After performing the above-described method for measuring the degree of crosslinking, 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 30 ml ampoule (Vial) and ultrapure water was added to obtain 25 g, and then the ampoule was placed in a constant temperature bath (90 ° C) to completely dissolve the PVA. After that, let it cool.

Add 20 mL of mannitol solution to the sample after cooling. Boron weight % (boron content (%)) was determined by titration with 0.1 N NaOH.

1.3 Boric acid crosslinking efficiency

Boric acid crosslinking efficiency = (degree of crosslinking of polarizer (%) × 10.81) / (boron content (%) × 3)

2. PVA Total Neck-in rate (%) - TD direction shrinkage

The width after the dry extension step and the width change of the polarizer produced after the dye extension step were calculated using the following shrinkage ratio to calculate the total shrinkage ratio.

All the shrinkage ratio (%) = (1 - (the length of the width after the dyeing extension step / the length of the width after the dry extension step)) * 100

Test Example - Evaluation of Inclined Unevenness

Using the adhesive, the polarizer produced in the above examples and comparative examples, and the COP (cycloolefin polymer) film (retardation film) manufactured by Zeon Co., Ltd., and the glass were used as the absorption axis of the polarizer. 45°, the slow axis of the first COP film is 15° with respect to the absorption axis of the polarizer, and the slow axis of the second COP film is 75° with respect to the absorption axis of the polarizer, sequentially stacking the polarizer, first COP film, second COP film and glass. The laminate was exposed to a high temperature environment at 80 ° C for 250 hours, and the degree of unevenness in the oblique direction was evaluated. The results of these are presented in Table 2 below.

In the case of Lv1.0, there is no unevenness at all. It means that the larger the value of Lv, the stronger the unevenness.

Lv1.0: No unevenness can be seen at all.

Lv2.0: See some slight unevenness.

Lv3.0: See the uneven orientation.

Lv4.0: See the overall oblique unevenness.

Lv5.0: See the overall obvious oblique unevenness.

As apparent from the above Table 2, the polarizer produced by the production method of the present invention does not undergo oblique unevenness after being exposed to a high temperature environment.

In the case of Example 11, the boric acid crosslinking efficiency within the range of the present invention was satisfied, and the TD shrinkage ratio was low, and the evaluation of the oblique unevenness was most excellent.

In contrast, the comparative example produced by deviating from the boric acid crosslinking efficiency of the present invention exhibited severe oblique unevenness after exposure to a high temperature environment, and it was confirmed that the optical characteristics were remarkably lowered.

Claims (15)

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 boronic acid cross-linking efficiency represented by the formula (1) of the polarizer produced is 4.0 to 5.5 Boric acid crosslinking efficiency = (degree of crosslinking of polarizer (%) × 10.81) / (boron content (%) × 3) (1) (wherein, the degree of crosslinking of the polarizer is the following formula (2) As shown, the boron content is the weight fraction (%) of boron contained in the polarizer; the degree of crosslinking (%) of the polarizer = (the absorbance integral value of the polarizer of 1200 to 1360 cm ^-1 / 2850 of the polarizer) integrated value of absorbance 3000cm ^-1) × 100 ... (2). The method for producing a polarizer according to claim 1, wherein the film has a shrinkage ratio in the TD direction of 25 to 40% before the wet step including stress relaxation, dyeing, and crosslinking. 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 20 to 80 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 of polarizing film according to any one of claims 1 to 5 In the method of the present invention, 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 extension ratio of the crosslinking step is 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.