WO2017078092A1

WO2017078092A1 - Polarizer and method for producing same

Info

Publication number: WO2017078092A1
Application number: PCT/JP2016/082655
Authority: WO
Inventors: 重萬朴; 容鉉權; 天煕趙; 正寧崔; 公彦矢可部
Original assignee: 住友化学株式会社
Priority date: 2015-11-05
Filing date: 2016-11-02
Publication date: 2017-05-11
Also published as: JP6942055B2; KR20170052991A; TWI762455B; TW201723541A; CN108351453B; CN108351453A; KR20180066100A; JPWO2017078092A1

Abstract

A polarizer which has an arithmetic mean height (Sa) of 21.0 nm or less.

Description

Polarizer and manufacturing method thereof

The present invention relates to a polarizer and a method for manufacturing the same, and more particularly to a polarizer having a small shrinkage force in the absorption axis (stretching) direction and less uneven stripes extending along the stretching direction with unevenness and a method for manufacturing the same. .

Polarizers used in various image display devices such as liquid crystal display devices (LCD), electroluminescence (EL) display devices, plasma display devices (PDP), field emission display devices (FED), OLEDs, etc. In particular, a polyvinyl alcohol (PVA) film includes a polarizer in which an iodine compound or a dichroic polarizing material is adsorbed and oriented, and a polarizer protective film is sequentially laminated on one surface of the polarizer. The other surface of the child has a multilayer structure in which a polarizer protective film, an adhesive layer bonded to another member, and a release film are sequentially laminated.

A polarizer constituting a polarizing plate is applied to an image display device, and is basically required to have both high transmittance and degree of polarization in order to provide an image having excellent color reproducibility. In order to embody this, a polarizer was manufactured by modifying the polyvinyl alcohol film itself or using a non-sublimation dichroic dye in place of the sublimable iodine polarization element.

On the other hand, a polarizer usually requires a stretching process in order to impart a polarizing function. However, after the polarizer is manufactured, there is a problem that the polarizer is deformed during use due to an inherent contraction force in the stretching (absorption axis) direction. The deformation of the polarizer causes a decrease in the optical function of the polarizer and a failure of the image display device.

Also, there is a problem that streaky unevenness extending along the stretching direction is generated with unevenness in the polarizer during the stretching process.

Japanese Published Patent Application No. 2010-145866 discloses a method of manufacturing a polarizer with a small shrinkage stress, but it does not present a satisfactory alternative to the above problem.

JP 2010-145866 A

An object of the present invention is to provide a polarizer having a small shrinkage force in the absorption axis direction and a method for manufacturing the same.
Another object of the present invention is to provide a polarizer having unevenness and reduced streak-like unevenness extending along the stretching direction, and a method for manufacturing the same.

1. A polarizer having an arithmetic average height (Sa) of 21.0 nm or less.

2. 2. The polarizer according to 1 above, having a thickness of 5 to 30 μm.

3. 3. The polarizer according to 1 or 2 above, wherein the contraction force in the absorption axis direction is 3 N / 2 mm or less.

4). Including swelling, dyeing, stretching, cross-linking, and drying steps of the polarizer-forming film,
The drying step includes a step of bringing the polarizer-forming film into contact with a hot roll and drying the film,
The method for producing a polarizer, wherein the time for bringing the polarizer-forming film into contact with a hot roll is 50% or more of the total drying time.

5. 5. The method for manufacturing a polarizer according to 4 above, wherein the drying step further includes a hot air drying step.

6. 6. The method for producing a polarizer according to 5 above, wherein the temperature of the hot roll is equal to or higher than the temperature of hot air.

7). The method for producing a polarizer according to any one of 4 to 6, wherein the dry neck-in value defined by the following formula 1 is 10 to 15%:
[Formula 1]
Dry neck-in = {(W1-W2) / W1} * 100 (%).
(W1 is the width of the polarizer-forming film before the drying step, and W2 is the width of the polarizer-forming film after the drying step).

8. A polarizing plate comprising the polarizer according to any one of 1 to 3 and a polarizer protective film bonded to at least one surface of the polarizer.

9. 10. An image display device comprising the polarizing plate as described in 9 above.

Since the polarizer of the present invention has a low arithmetic average height, it exhibits a low shrinkage force in the absorption axis direction, and can remarkably reduce streaky unevenness extending along the stretching direction with unevenness.

In the method for producing a polarizer of the present invention, the drying neck-in value is adjusted to a specific range by drying the polarizer-forming film in contact with a hot roll for a specific time, and in the absorption axis direction. It is possible to manufacture a polarizer that exhibits a low contraction force and has markedly reduced streak-like unevenness extending along the stretching direction with unevenness.

In the present invention, since the arithmetic average height (Sa) is 21.0 nm or less, the contraction force is low in the absorption axis direction, and the generation of streaky unevenness extending along the stretching direction with unevenness is reduced. The present invention relates to a child and a manufacturing method thereof.

Hereinafter, the present invention will be described in detail.

Normally, a polarizer produced by stretching a polarizer-forming film starts to shrink during drying during the manufacturing process, but excessive drying neck-in occurs during such shrinking process, resulting in unevenness. There is a problem that streaky unevenness extending along the stretching direction occurs. In addition, the contraction force in the absorption axis direction that could not be sufficiently resolved occurs when the polarizer applied to the image display device or the like subsequently receives heat from the outside, resulting in deformation of the polarizer. .

Accordingly, the arithmetic average height (Sa) of the polarizer of the present invention is adjusted to 21.0 nm or less, so that the stripe-like unevenness extending along the stretching direction with the contraction force and the unevenness in the absorption axis direction is noticeable. Can be reduced.

The inventor of the present invention, when the film for forming a polarizer is in contact with a hot roll and is dried, the film for forming a polarizer is supported by the hot roll, and in the width direction of the polarizer (direction perpendicular to the stretching direction). By controlling the shrinkage, the unevenness generated by the deformation in the width direction of the polarizer is suppressed, so that streaky unevenness extending along the stretching direction with the unevenness is suppressed. Further, by controlling the contraction in the width direction of the polarizer, the thickness of the polarizer-forming film is further reduced by that amount, and the contraction force in the stretching (absorption axis) direction of the polarizer is reduced. Although it is determined as described above, it should not be interpreted as being limited to this.

The inventor of the present invention also adjusts the arithmetic average height (Sa) of the polarizer to 21.0 nm or less to reduce the shrinkage force in the absorption axis direction and to extend along the stretching direction with unevenness. The unevenness of the shape was remarkably reduced. If the arithmetic average height of the polarizer is 21.0 nm or less, the intended effect of the present invention is achieved, so the lower limit thereof is not particularly limited. For example, 1.0 nm or more, 0.1 nm or more, or 0 nm It may be super. The arithmetic average height of the polarizer may be 21.0 nm or less, but is preferably 19.0 nm or less, and more preferably 17.0 nm or less. The arithmetic average height (Sa) can be measured based on, for example, ISO 25178. In the present invention, in order to adjust the arithmetic average height (Sa) of the polarizer to 21.0 nm or less, it can be adjusted by controlling the ratio of the hot roll drying time in the total drying time to 50% or more. it can.

The polarizer of the present invention in which the arithmetic average height is adjusted may have a thickness relatively lower than that of a normal polarizer, and the lower limit of the thickness of the polarizer is 5 μm from these side faces. It may be 7 μm. The upper limit of the thickness of the polarizer may be 30 μm, 28 μm, or 23 μm. In this invention, in order to adjust the thickness of a polarizer to the above-mentioned range, it can adjust by controlling the ratio of the hot roll drying time in the total drying time to 50% or more.

On the other hand, as described above, the polarizer of the present invention has a low contraction force in the absorption axis direction. For example, the contraction force in the absorption axis direction may be 3 N / 2 mm or less. When the contraction force in the absorption axis direction is 3 N / 2 mm or less, deformation of the polarizer can be effectively prevented. The lower the shrinkage force in the absorption axis direction, the better. Therefore, the lower limit thereof is not particularly limited, and may be, for example, 2 N / 2 mm or more, 1 N / 2 mm or more, or 0.1 N / 2 mm or more. In the present invention, in order to adjust the contraction force of the polarizer to the above-described range, it can be adjusted by controlling the ratio of the hot roll drying time in the total drying time to 50% or more.

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

The method for producing a polarizer of the present invention includes a step of swelling, dyeing, stretching, cross-linking and drying of a film for forming a polarizer, and the drying step comprises a step of drying the film for forming a polarizer by contacting with a hot roll. And the time for which the polarizer-forming film is brought into contact with the hot roll is 50% or more of the total drying time.

The manufacturing method of the polarizer of the present invention will be described more specifically as follows.

As long as the film for forming a polarizer for producing a polarizer is a polymer film used for producing a polarizing plate, a film that can be dyed with a dichroic substance (for example, iodine) known in the art is not particularly limited. For example, polyvinyl alcohol film, partially saponified polyvinyl alcohol film; polyethylene terephthalate film, ethylene-vinyl acetate copolymer film, ethylene-vinyl alcohol copolymer film, cellulose film, partially A hydrophilic polymer film such as a saponified film, or a polyene oriented film such as a dehydrated polyvinyl alcohol film or a dehydrochlorinated polyvinyl chloride film can be used. 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.

The method for producing a polarizer according to the present invention may include a swelling step, a dyeing step, a crosslinking step, a complementary color step, a stretching step, a water washing step, and a drying step, and can be classified according to a stretching method. For example, a dry stretching method, a wet stretching method, or a hybrid stretching method in which the above-mentioned two kinds of stretching methods are mixed can be used. Below, although the manufacturing method of the polarizer of this invention is demonstrated taking the wet extending | stretching method as an example, it is not restrict | limited to this.

Among the above steps, the remaining steps except the drying step are the states in which the film for forming the polarizer is immersed in a constant temperature bath (bath) filled with one or more solutions each selected from various types of solutions. Can be done.

<Swelling step>
The swelling step is performed by immersing the unstretched polarizer-forming film in a swelling tank filled with a swelling aqueous solution before dyeing it, and depositing impurities on the surface of the polarizer-forming film, such as impurities or antiblocking agents. Are steps for swelling the polarizer forming film, improving the stretching efficiency, preventing uneven dyeing, and improving the physical properties of the polarizer.

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

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

As the performance time of the swelling step (swelling bath immersion time), a performance time known in the art can be applied without particular limitation, and may be, for example, 180 seconds or less, preferably 150 seconds or less. . When the immersion time is in the above range, it is possible to suppress the swelling from becoming excessively saturated, and the breakage due to the softening of the polarizer forming film is prevented, and the adsorption of iodine becomes uniform in the dyeing step. The degree of polarization can be improved.

The stretching step can be performed together with the swelling step. At this time, the stretching ratio may be about 1.1 to 3.5 times, but is not limited, and preferably 1.3 to 3.0 times. Good. If the draw ratio is less than 1.1 times, wrinkles may occur. If it exceeds 3.5 times, the initial optical characteristics may be weak.

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

As the aqueous dye solution, an aqueous dye solution known in the art can be used without particular limitation, and it can contain water, a water-soluble organic solvent or a mixed solvent thereof and iodine. The iodine content may be 0.4 to 400 mmol / L in the aqueous dyeing solution, but is not limited thereto, and is preferably 0.8 to 275 mmol / L, most preferably 1 to 200 mmol / L. Also good.

The aqueous solution for dyeing may further contain an iodide as a solubilizing agent so that the dyeing efficiency can be improved. As the iodide, an iodide known in the art can be used without limitation. For example, potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, iodide At least one selected from the group consisting of barium iodide, calcium iodide, tin iodide, and titanium iodide can be included, and among these, potassium iodide is preferable because of its high solubility in water. The iodide content may be 0.01 to 10% by weight with respect to 100% by weight of water, but is not limited, and may preferably be 0.1 to 5% by weight.

In order to increase the iodine complex content in the polarizer-forming film, boric acid may be added to the dyeing tank in an amount of 0.3 to 5% by weight with respect to 100% by weight of water. Not. When boric acid dyeing tank is less than 0.3 wt%, _{PVA-I 3} ^- complex and _{PVA-I 5} ^- it may not be effective in increasing the complex content, boric acid dyeing tank 5 If the concentration is higher than% by weight, the risk of film breakage may increase.

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

In the present invention, the stretching step can be performed together with the dyeing step. At this time, the stretching ratio may be 1.01 to 2.0 times, but is not limited thereto, and preferably 1. It may be 1 to 1.8 times.

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

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

When iodine, which is a dichroic dye, has insufficient crosslinking reaction, iodine molecules may be detached by a moist heat environment, and sufficient crosslinking reaction is required. Further, in order to orient the iodine molecules located between the molecules of the polarizer-forming film and improve the optical properties, stretching at the largest stretching ratio can be performed in the crosslinking step.

In the present invention, the method for producing a polarizer can perform a crosslinking step known in the art without particular limitation, for example, can perform a crosslinking step constituted by a first and a second crosslinking step, One or more of the first and second crosslinking steps can use an aqueous solution for crosslinking containing a boron compound. This can improve the optical properties and color durability of the polarizer.

As the aqueous solution for crosslinking, a known aqueous crosslinking solution can be used without particular limitation. For example, the aqueous solution for crosslinking may contain water as a solvent and a boron compound such as boric acid or sodium borate. It may further contain an organic solvent and iodide that are mutually soluble.

Boron compounds impart short crosslinks and stiffness to the polarizer, and can suppress wrinkling of the film during the process, improving the handleability of the film and forming the iodine orientation of the polarizer Can play a role.

The boron compound content may be a content known in the art, and may be, for example, 1 to 10% by weight, preferably 2 to 6% by weight with respect to 100% by weight of water. Good. When the content is less than 1% by weight, the crosslinking effect of the boron compound is reduced, and it may be difficult to impart rigidity to the polarizer. When the content exceeds 10% by weight, the crosslinking reaction of the inorganic crosslinking agent is excessive. When activated, the crosslinking reaction of the organic crosslinking agent may not proceed effectively.

In this step, iodide can be used to maintain the uniformity of the degree of polarization in the plane of the polarizer and to prevent desorption of dyed iodine. The iodide may be the same as that used in the dyeing step, and its content may be 0.05 to 15% by weight with respect to 100% by weight of water, but is not limited, preferably May be from 0.5 to 11% by weight. If the content is less than 0.05% by weight, iodine ions in the film may escape and increase the transmittance of the polarizer. If the content exceeds 15% by weight, iodine ions in the aqueous solution may be added to the film. It can penetrate and reduce the transmittance of the polarizer.

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

The stretching step can be performed together with the crosslinking step, and at this time, the stretching ratio of the first crosslinking step may be 1.4 to 3.0 times, preferably 1.5 to 2.5 times. May be.

Further, the stretching ratio of the second crosslinking step may be 1.01 to 2.0 times, preferably 1.2 to 1.8 times.

Further, the cumulative draw ratio of the first and second crosslinking steps may be 1.5 to 5.0 times, but is not limited thereto, and preferably 1.7 to 4.5 times. Good. If the cumulative stretching ratio is less than 1.5 times, the orientation effect of iodine may be insufficient, and if it exceeds 5.0 times, the film may break due to excessive stretching. Yes, production efficiency can be reduced.

<Complementary color step>
The manufacturing method of the polarizer of this invention may further include the complementary color step as needed. Through the complementary color step, the iodine complex positioned between the molecules in the polarizer-forming film on which the iodine complex is physically adsorbed can be oriented near the boric acid bridge to stabilize the iodine complex. . Further, through the complementary color step, the color can be corrected for the polarizer-forming film in which the iodine complex is not sufficiently dyed in the crosslinking step.

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

In the present invention, the boron compound imparts short crosslinks and rigidity to the polarizer, and suppresses wrinkling of the film during the process, thereby improving the handleability of the film and improving the iodine orientation of the polarizer. Can play a role to form.

The content of the boron compound may be 1 to 10% by weight with respect to 100% by weight of water, but is not limited thereto, and may preferably be 2 to 6% by weight. When the content is less than 1% by weight, the crosslinking effect of the boron compound is reduced, and it may be difficult to impart rigidity to the polarizer. When the content exceeds 10% by weight, the crosslinking reaction of the inorganic crosslinking agent is excessive. When activated, the crosslinking reaction of the organic crosslinking agent may not proceed effectively.

In this step, iodide can be used to maintain the uniformity of the degree of polarization in the plane of the polarizer and to prevent desorption of dyed iodine. The iodide may be the same as that used in the dyeing step, and the content may be 0.05 to 15% by weight with respect to 100% by weight of water, but is not limited thereto. Preferably, it may be 0.5 to 11% by weight. If the content is less than 0.05% by weight, iodine ions in the film may escape and increase the transmittance of the polarizer. If the content exceeds 15% by weight, iodine ions in the aqueous solution may be added to the film. It can penetrate and reduce the transmittance of the polarizer.

In the present invention, the temperature of the complementary color tank may be 20 to 70 ° C. The immersion time of the polarizer-forming film in the complementary color tank may be 1 second to 15 minutes, but is not limited thereto, and may preferably be 5 seconds to 10 minutes.

The stretching step can be performed together with the complementary color step. At this time, the stretching ratio of the complementary color step may be 1.01 to 1.1 times, but is not limited thereto, and preferably 1.02 to 1. It may be 08 times.

If the draw ratio is less than 1.01, the stabilization effect of the iodine complex may be insufficient, and if it exceeds 1.1 times, the film may be broken by excessive stretching. Production efficiency can be reduced.

<Extension step>
In the present invention, the stretching step may be performed simultaneously with other steps as described above, or may be performed separately.

Further, the stretching step may be performed at least once or may be performed a plurality of times. When it is performed a plurality of times, it may be performed separately at an arbitrary step in the manufacturing process of the polarizer.

In the production method of the present invention, the total cumulative draw ratio of the polarizer is preferably 4.0 to 7.0 times, and more preferably 5.3 to 6 times.

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

<Washing step>
The polarizer production method of the present invention is, as necessary, for immersing a film for forming a polarizer, which has been crosslinked and stretched, in a washing tank filled with an aqueous washing solution, and for forming a polarizer in steps up to the washing step. A water washing step may be further included to remove unwanted residues such as boric acid attached to the film.

In the present invention, the aqueous washing solution may be an aqueous washing aqueous solution known in the art without particular limitation, and may be, for example, water, to which an iodide may be further added. Not.

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

The water washing step can be omitted, and can be performed each time a step before the water washing step such as the dyeing step or the crosslinking step is completed. Further, it may be repeated one or more times, and the number of repetitions is not particularly limited.

<Drying step>
In the production method of the present invention, the drying step is a step of drying the washed film for forming a polarizer, and further improves the orientation of dyed iodine molecules by neck-in by drying. This is a step of obtaining a polarizer having excellent optical characteristics. Neck-in means that the width of the film is narrowed.

The drying step according to the present invention includes a step of bringing the polarizer-forming film into contact with a hot roll and drying, and the time for bringing the polarizer-forming film into contact with the hot roll is 50% or more of the total drying time.

As discussed above, the present invention can achieve the intended effect in the present invention by bringing the polarizer-forming film into contact with a hot roll and drying it. Is adjusted to 50% or more of the total drying time. Specifically, the time for bringing the polarizer-forming film into contact with the heat roll may be 30 to 600 seconds, preferably 40 to 120 seconds, more preferably 40 to 60 seconds, 42 It is particularly preferable that the time is ˜58 seconds.

In the present invention, the hot roll means a roll heated at a temperature higher than the ambient temperature. For example, the heat roll may have a temperature about 5 to 20 ° C. higher than the ambient temperature. There may be one heat roll or a plurality of heat rolls.

In the present invention, the total drying time is the time for performing the drying step, and refers to the time during which any drying method is performed on the polarizer-forming film. For example, if drying is performed by contacting with a heat roll, the time for contacting the film with the heat roll, the time for transporting the film between the heat rolls when using a plurality of heat rolls, hot air drying If hot air is applied to the film, if air drying is applied, air is applied to the film, if heated, the film is heated, if far infrared is applied, the film is irradiated with far infrared light. In the case of microwave drying, the time during which the film is irradiated with microwaves is included in the total drying time. Accordingly, the total drying time includes a time during which a drying method other than the method of drying the polarizer-forming film in contact with a hot roll is performed.

In the present invention, when the time for the polarizer-forming film to contact the heat roll is 50% or more of the total drying time, it becomes easy to produce a polarizer having an arithmetic average height (Sa) of 21.0 nm or less, The stripe-shaped unevenness | corrugation extended along the extending | stretching direction with the shrinkage force and unevenness | corrugation of the absorption axis direction of the manufactured polarizer can be reduced.

In the drying step according to the present invention, the neck-in value of the polarizer can be adjusted. For example, the dry neck-in value defined by Equation 1 below may be 10 to 15%. :
[Formula 1]
Dry neck-in = {(W1-W2) / W1} * 100 (%)
(W1 is the width of the polarizer-forming film before the drying step, and W2 is the width of the polarizer-forming film after the drying step).
In the present invention, in order to adjust the drying neck-in value of the polarizer to the above-mentioned range, it can be adjusted by controlling the ratio of the hot roll drying time in the total drying time to 50% or more.

When the dry neck-in value is in the above range, the effect of reducing the shrinkage force in the absorption axis direction and unevenness in the stretching direction can be more remarkable.

In the present invention, the drying step can be accompanied by hot air drying together with the contact of the polarizer-forming film with the hot roll. At this time, the temperature of the hot air may be, for example, 20 to 100 ° C., and the temperature of the hot roll can be set higher than the temperature of the hot air, for example, can be set higher by 5 to 20 ° C. The temperature of the heat roll is preferably 100 ° C. or less from the viewpoint of preventing deterioration of the polarizer.

The total drying time is not particularly limited, and can be performed, for example, for 1 to 10 minutes. Of the total drying time, the drying time with hot air is not particularly limited, and can be performed, for example, for 0 to 2 minutes.

In the present invention, in addition to hot air drying, drying methods known in the art can be used in combination without limitation, and for example, methods such as air drying, heat drying, far-infrared drying, and microwave drying can be used.

The polarizer according to the present invention can be provided as a polarizing plate with a polarizer protective film bonded to at least one surface.

The material of the polarizer protective film is not particularly limited. For example, various transparent resin films including at least one selected from the group consisting of an acrylic resin film, a cellulose resin film, a polyolefin resin film, and a polyester resin film are used. Can be used.

Specific examples of the protective film include acrylic resin films such as polymethyl (meth) acrylate and polyethyl (meth) acrylate; polyester resin films such as polyethylene terephthalate, polyethylene isophthalate, polyethylene naphthalate, and polybutylene terephthalate; Cellulose-based resin films such as diacetylcellulose, triacetylcellulose, and cellulose acetate propionate; polyolefin-based resin films such as polyethylene, polypropylene, polyolefins having a cyclo- or norbornene structure, and ethylene-propylene copolymers; However, it is not limited to these.

The thickness of the protective film is not particularly limited, but may be 10 to 200 μm, preferably 10 to 150 μm. When a polarizer protective film is laminated on both sides of the polarizer, each protective film may be the same or have a different thickness.

Bonding of the polarizer and the polarizer protective film may be performed using an adhesive composition. Bonding of the polarizer and the protective film using the adhesive composition can be performed by an appropriate method, such as casting method, Mayer bar coating method, gravure coating method, die coating method, dip coating method, spraying method, etc. The method of apply | coating an adhesive composition to the adhesive surface of a polarizing film and / or a protective film, and making both overlap is mentioned. The casting method is a method in which an adhesive composition is applied to the surface of an object to be coated while moving a polarizer or a protective film to be coated in a substantially vertical direction, a substantially horizontal direction, or an oblique direction therebetween. .

After applying the adhesive composition, the polarizer and the protective film are sandwiched by nip rolls and bonded.

Also, in order to improve the adhesion, the surface of the polarizer and / or the protective film can be appropriately subjected to surface treatment such as plasma treatment, corona treatment, ultraviolet irradiation treatment, flame treatment, saponification treatment. Examples of the saponification treatment include a method of immersing in an aqueous solution of an alkali such as sodium hydroxide or potassium hydroxide.

After laminating the polarizer and the polarizer protective film, a drying process is performed. The drying process is performed, for example, by spraying hot air, and the temperature at that time is appropriately selected in the range of 50 to 100 degrees. The drying time is usually 30 to 1,000 seconds.

The polarizing plate according to the present invention is applicable not only to a normal liquid crystal display device but also to various image display devices such as an organic electroluminescence display device (OLED), a plasma display device, and a field emission display device.

The following examples are presented to assist in understanding 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 technical idea, and these changes and modifications should be within the scope of the appended claims.

<Example 1>
A transparent unstretched polyvinyl alcohol film (PE60, KURARAY) having a saponification degree of 99.9% or more was swelled by immersing it in water (deionized water) at 25 ° C. for 2 minutes (swelling step), and then iodine. Dyeing was performed by immersing in an aqueous dyeing solution at 30 ° C. containing 1.1% by weight of potassium iodide and 0.3% by weight of boric acid with respect to 2.0 mM / L and 100% by weight of water for 2 minutes and 14 seconds. (Dyeing step). At this time, the film was stretched at a stretching ratio of 1.482 times and 1.607 times in the swelling and dyeing steps, respectively. Next, it was immersed in an aqueous solution for crosslinking at 53 ° C. containing 11.0% by weight of potassium iodide and 4% by weight of boric acid with respect to 100% by weight of water for 39 seconds (crosslinking step). The film was stretched at a double stretch ratio. Next, the film was stretched 1.05 times while immersed in a complementary color aqueous solution at 40 ° C. containing 11% by weight of potassium iodide and 4% by weight of boric acid with respect to 100% by weight of water (complementary color step).

The crosslinked polyvinyl alcohol film was washed with deionized water (water washing step) and then dried using a hot roll and hot air (drying step) to produce a polarizer having a transmittance of 42.5%. Specific conditions of the hot roll and hot air are as described in Table 1 below.

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

<Examples 2 to 9 and Comparative Examples 1 to 5>
As described in Table 1 below, a polarizing plate was produced in the same manner as in Example 1 except that the temperature and drying time of the hot roll and hot air were adjusted.

<Test example>
The physical properties of the polarizers and polarizing plates produced in the above Examples and Comparative Examples were measured by the following methods, and the results are shown in Table 2 below.

<1. Dry NECK-IN measurement>
The dry NECK-IN, which means the rate of decrease of the polarizer before and after drying, was measured according to the above Equation 1.

<2. Measurement of unevenness>
After production of the polarizing plate, the presence or absence of visual recognition of streaky unevenness extending along the stretching direction with unevenness was visually confirmed by the fluorescent lamp reflection method according to the following criteria. The fluorescent lamp reflection method is an evaluation method in which light from a fluorescent lamp is incident from an oblique direction of about 45 °, and unevenness of a polarizing plate is visually confirmed with reflected light.
Lv1. : Level in which unevenness cannot be confirmed in the obtained polarizing plate Lv2. : In the obtained polarizing plate, unevenness can be visually recognized by the fluorescent lamp reflection method but cannot be visually confirmed Lv3. : In the obtained polarizing plate, unevenness can be visually recognized by the fluorescent lamp reflection method, and visually visible level.

<3. PVA surface arithmetic average height (Sa) measurement>
After the manufactured polarizer was cut into a size of 1 cm × 1 cm, the arithmetic average height in the plane of the polarizer was measured based on ISO 25178-2 using a surface interferometer (ZYGO, manufactured by MetroPro).

<4. Contraction force measurement>
Here, the contraction force in the absorption axis direction per 2 mm width in the transmission axis direction of the polarizer was measured. The polarizers produced in the examples and comparative examples were cut to a size of 3.0 cm (absorption axis direction) × 2 mm (transmission axis direction), and then DMA Q800 (Dynamic mechanical analyzer, TA) at 80 ° C. for 4 hours. The shrinkage force in the absorption axis direction was measured at the time of standing. At this time, in order to maintain the polarizer in a flat state before the measurement, the minimum load was applied in the thickness direction of the polarizer.

<5. Optical properties (degree of polarization)>
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 2 below.
[Formula 2]
Polarization degree (P) = [(T ₁ −T ₂ ) / (T ₁ + T ₂ )] ^1/2
(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).

Referring to Table 2, the polarizer having undergone the drying step of the present invention has unevenness compared to the whole of the comparative example, although the degree of polarization is almost inferior to that of Comparative Examples 3 and 5 dried only with hot air. Accordingly, it can be confirmed that the stripe-shaped unevenness extending along the stretching direction and the contraction force in the absorption axis direction are greatly reduced.

Claims

A polarizer having an arithmetic average height (Sa) of 21.0 nm or less.
The polarizer according to claim 1, wherein the thickness is 5 to 30 μm.
The polarizer according to claim 1 or 2, wherein the contraction force in the absorption axis direction is 3 N / 2 mm or less.
Including swelling, dyeing, stretching, cross-linking, and drying steps of the polarizer-forming film,
The drying step includes a step of bringing the polarizer-forming film into contact with a hot roll and drying the film,
The method for producing a polarizer, wherein the time for bringing the polarizer-forming film into contact with a hot roll is 50% or more of the total drying time.
The method for producing a polarizer according to claim 4, wherein the drying step further includes a hot air drying step.
The method for producing a polarizer according to claim 5, wherein the temperature of the hot roll is equal to or higher than the temperature of hot air.
The method for producing a polarizer according to any one of claims 4 to 6, wherein the dry neck-in value defined by the following formula 1 is 10 to 15%:
[Formula 1]
Dry neck-in = {(W1-W2) / W1} * 100 (%).
(W1 is the width of the polarizer-forming film before the drying step, and W2 is the width of the polarizer-forming film after the drying step).
A polarizing plate comprising the polarizer according to any one of claims 1 to 3 and a polarizer protective film bonded to at least one surface of the polarizer.
An image display device comprising the polarizing plate according to claim 8.