JP6942055B2 - Polarizer and its manufacturing method - Google Patents

Description

The present invention relates to a polarizer and a method for producing the same, and more specifically, to a polarizer having a small shrinkage force in the absorption axis (stretching) direction and having unevenness and having less streak-like unevenness extending along the stretching direction and a method for producing the same. ..

Polarizing plates used in various image display devices such as liquid crystal displays (LCD), electric field emission (EL) display devices, plasma display devices (PDP), electric field emission display devices (FED), and OLEDs are generally used. A polyvinyl alcohol-based (PVA) film contains a polarizer in which an iodine-based compound or a dichroic polarizing substance is adsorbed and oriented, and a polarizing element protective film is sequentially laminated on one surface of the polarizing element to polarize the polarized light. The other surface of the child has a multilayer structure in which a polarizing element protective film, an adhesive layer to be bonded to other members, and a release film are laminated in this order.

The polarizing element constituting the 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 realize this, a polarizer was produced by modifying the polyvinyl alcohol-based film itself or using a non-sublimable dichroic dye instead of the sublimable iodine-based polarizing element.

On the other hand, normally, a polarizing element requires a stretching step in order to impart a polarizing function, but after being manufactured, there is a problem that the polarizer is deformed during use due to an inherent contraction force in the stretching (absorption axis) direction. Deformation of the polarizer causes deterioration of the optical function of the polarizer and failure of the image display device.

In addition, there is also a problem that streaky unevenness extending along the stretching direction occurs due to unevenness of the polarizer during the stretching step.

Japanese Patent No. 2010-145866 discloses a method for producing a polarizer having a small shrinkage stress, but has not been able to present a satisfactory alternative to the above problems.

Japanese Unexamined Patent Publication No. 2010-145866

An object of the present invention is to provide a polarizer having a small contraction force in the absorption axis direction and a method for producing 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 producing the same.

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

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

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

4. Includes swelling, dyeing, stretching, cross-linking, and drying steps of the polarizing film.
The drying step includes a step of bringing the polarizing film to be brought into contact with a heat roll to dry it.
A method for producing a polarizer, in which the time for contacting the polarizing film for forming a polarizer with a heat roll is 50% or more of the total drying time.

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

6. 5. The method for producing a polarizer according to 5 above, wherein the temperature of the heat 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 above, 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 (%).
(In the formula, 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 including the polarizer according to any one of 1 to 3 above and a polarizer protective film bonded to at least one surface of the polarizer.

9. An image display device including the polarizing plate according to the above 9.

Since the polarizer of the present invention has a low arithmetic mean height, it exhibits a low shrinkage force in the absorption axis direction, and can remarkably reduce streak-like 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 contacting the polarizing film for forming a film with a heat roll and drying it for a specific time, and the drying neck-in value is adjusted in a specific range in the absorption axis direction. It is possible to produce a polarizer that exhibits low shrinkage force and has remarkably reduced streak-like unevenness extending along the stretching direction with unevenness.

In the present invention, since the arithmetic mean height (Sa) is 21.0 nm or less, the contraction force is low in the absorption axis direction, and the occurrence of streak-like unevenness extending along the stretching direction with unevenness is reduced. Regarding the child and its manufacturing method.

Hereinafter, the present invention will be described in detail.

Normally, a polarizer produced by stretching a film for forming a polarizer causes shrinkage during drying during the manufacturing process, but excessive drying neck-in is generated during such shrinkage process, resulting in unevenness. There is a problem that streak-like unevenness extending along the stretching direction occurs. In addition, there is a problem that the contraction force in the absorption axis direction, which could not be sufficiently eliminated, is manifested when the polarizer applied to an image display device or the like subsequently receives heat from the outside, resulting in deformation of the polarizer. ..

Therefore, in the polarizer of the present invention, by adjusting the arithmetic mean height (Sa) to 21.0 nm or less, streak-like unevenness extending along the stretching direction with contraction force and unevenness in the absorption axis direction becomes remarkable. It can be reduced.

According to the inventor of the present invention, when the polarizing film is brought into contact with a thermal roll and dried, the polarizing film is supported by the thermal roll in the width direction of the polarizer (direction perpendicular to the stretching direction). By controlling the contraction, the unevenness generated by the deformation of the polarizer in the width direction is suppressed, so that the streak-like unevenness that accompanies the unevenness and extends along the stretching direction is suppressed. Further, by controlling the contraction of the polarizer in the width direction, the thickness of the film for forming the polarizer is further reduced by that amount, and the contraction force in the stretching (absorption axis) direction of the polarizer is reduced. Judgment is made as above, but it should not be construed as limited to this.

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

The polarizer of the present invention in which the arithmetic mean 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 from these aspects is 5 μm. It may be 7 μm. The upper limit of the thickness of the polarizer may be 30 μm, 28 μm, or 23 μm. In the present invention, in order to adjust the thickness of the polarizer within the above range, it can be adjusted by controlling the ratio of the thermal roll drying time to the total drying time to 50% or more.

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

The present invention also provides the above-mentioned method for producing a polarizer.

The method for producing a polarizer of the present invention includes a step of swelling, dyeing, stretching, cross-linking and drying a polarizing film, and the drying step includes a step of contacting the polarizing film with a heat roll to dry the film. Including, the time for contacting the polarizer-forming film with the heat roll is 50% or more of the total drying time.

A more specific description of the method for producing a polarizer of the present invention is as follows.

The film for forming a polarizer for producing a polarizer is not particularly limited to a film that can be dyed with a bicolor substance (for example, iodine) known in the art as long as it is a polymer film used for producing a polarizing plate. It can be used, 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 of these. A hydrophilic polymer film such as a saponified film; or a polyene oriented film such as a dehydrated polyvinyl alcohol-based film or a dehydrogenated polyvinyl chloride-based film; can be used. Among these, a polyvinyl alcohol-based film is preferable in that it not only has an excellent effect of enhancing the uniformity 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 can include a swelling step, a dyeing step, a cross-linking step, a complementary color step, a stretching step, a washing step and a drying step, and can be classified according to the stretching method. For example, a dry stretching method, a wet stretching method, or a hybrid stretching method in which the above two types of stretching methods are mixed can be mentioned. Hereinafter, the method for producing a polarizer of the present invention will be described by taking the wet stretching method as an example, but the method is not limited thereto.

In the remaining steps except the drying step in the above steps, the polarizer film is immersed in a constant temperature water bath (bath) filled with one or more solutions selected from various kinds of solutions. Can be done with.

<Swelling step>
The swelling step is to immerse the unstretched polarizing film before dyeing it in a swelling tank filled with an aqueous solution for swelling, and impurities such as dust or anti-blocking agents deposited on the surface of the polarizing film. This is a step for removing the above-mentioned material, swelling the film for forming a polarizer, improving the stretching efficiency, preventing dyeing non-uniformity, and improving the physical properties of the polarizer.

As the swelling aqueous solution, a swelling aqueous solution 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, the processability can be improved as well as the 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.

The execution time of the swelling step (immersion time in the swelling tank) can be applied without particular limitation to the execution time known in the art, and may be, for example, 180 seconds or less, preferably 150 seconds or less. .. When the immersion time is within the above range, it is possible to prevent the swelling from becoming excessively saturated, prevent breakage due to softening of the polarizingt-forming film, and make iodine adsorption uniform in the dyeing step. , The degree of polarization can be improved.

The stretching step can be performed together with the swelling step, and the stretching ratio may be about 1.1 to 3.5 times, but is not limited, and may be preferably 1.3 to 3.0 times. good. If the draw ratio is less than 1.1 times, wrinkles may occur, and if it exceeds 3.5 times, the initial optical characteristics may become 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 solution for dyeing containing iodine, and adsorbing iodine on the polarizer-forming film.

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

The aqueous solution for dyeing may further contain iodide as a solubilizing agent so that the dyeing efficiency can be improved. As the iodide, 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. It can contain at least one selected from the group consisting of barium iodide, calcium iodide, tin iodide, and titanium iodide, of which potassium iodide is preferred because of its high solubility in water. The content of iodide may be 0.01 to 10% by weight, but is not limited, and may be preferably 0.1 to 5% by weight based on 100% by weight of water.

Further, in order to increase the content of the iodine complex in the film for forming the polarizer, boric acid may be added to the dyeing tank in an amount of 0.3 to 5% by weight based on 100% by weight of water, but this is limited. Not done. When boric acid dyeing tank is less than 0.3 wt%, _{PVA-I 3} ^- complex and _{PVA-I 5} ^- may not be effective in increasing the complex content, boric acid dyeing tank 5 At concentrations higher than% by weight, the risk of film breakage can be high.

The temperature of the dyeing tank may be 5 to 42 ° C, but is not limited to this, and may be preferably 10 to 35 ° C. Further, the immersion time of the polarizing element forming film 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, and at this time, the stretching ratio may be 1.01 to 2.0 times, but is not limited to this, and is preferably 1. It may be 1 to 1.8 times.

Further, the cumulative stretching ratio up to the dyeing step including the swelling and the dyeing step may be 1.2 to 4.0 times. If the cumulative draw ratio is less than 1.2 times, wrinkles of the film may occur and poor appearance may occur, and if it exceeds 4.0 times, the initial optical characteristics may become weak.

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

If the cross-linking reaction of iodine, which is a dichroic dye, is insufficient, iodine molecules may be desorbed due to a moist heat environment, and a sufficient cross-linking reaction is required. Further, in order to orient the iodine molecules located between the molecules of the polarizer-forming film and to improve the optical properties, stretching at the maximum stretching ratio can be performed in the cross-linking step.

In the present invention, the method for producing a polarizer can carry out a cross-linking step known in the art without particular limitation, for example, a cross-linking step composed of the first and second cross-linking steps. For one or more of the first and second cross-linking steps, a cross-linking aqueous solution containing a boron compound can be used. This can improve the optical properties and color durability of the polarizer.

As the cross-linking aqueous solution, a cross-linking aqueous solution known in the art can be used without particular limitation, and may contain, for example, water as a solvent and a boron compound such as boric acid or sodium borate, together with water. It may further contain a mutually soluble organic solvent and iodide.

The boron compound imparts short cross-linking bonds and rigidity to the polarizer and suppresses wrinkles in the film during the process, thereby improving the handleability of the film and forming the iodine orientation of the polarizer. Can play a role.

As the content of the boron compound, a content known in the art can be applied, for example, it may be 1 to 10% by weight, preferably 2 to 6% by weight, based on 100% by weight of water. good. If the content is less than 1% by weight, the cross-linking effect of the boron compound may be reduced and it may be difficult to impart rigidity to the polarizer, and if it exceeds 10% by weight, the cross-linking reaction of the inorganic cross-linking agent may be excessive. It may be activated and it may be difficult for the cross-linking reaction of the organic cross-linking agent to proceed effectively.

In this step, the iodide can be used to maintain the uniformity of polarization in the plane of the polarizer and to prevent the 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 based on 100% by weight of water, but is not limited and is preferable. May be 0.5 to 11% by weight. If the content is less than 0.05% by weight, iodide ions in the film may escape and increase the transmittance of the polarizer, and if it exceeds 15% by weight, the iodide ions in the aqueous solution may be transferred to the film. It can penetrate and reduce the transmittance of the polarizer.

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

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

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

Further, the cumulative stretching ratio of the first and second cross-linking steps may be 1.5 to 5.0 times, but is not limited to this, and may be 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 be broken due to excessive stretching. Yes, production efficiency can be reduced.

<Complementary color step>
The method for producing a polarizer of the present invention may further include a complementary color step, if necessary. Through the complementary color step, the iodine complex located between the molecules in the polarizer-forming film on which the iodine complex is physically adsorbed can be oriented near the borate bridge to stabilize the iodine complex. .. Further, through the complementary color step, it is possible to correct the color of the polarizer-forming film in which the iodine complex is not sufficiently dyed in the cross-linking step.

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

In the present invention, the boron compound imparts short cross-linking and rigidity to the polarizer and suppresses wrinkles in the film during the process, thereby improving the handleability of the film and adjusting the iodine orientation of the polarizer. Can play a role in forming.

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 to this, and may be preferably 2 to 6% by weight. If the content is less than 1% by weight, the cross-linking effect of the boron compound may be reduced and it may be difficult to impart rigidity to the polarizer, and if it exceeds 10% by weight, the cross-linking reaction of the inorganic cross-linking agent may be excessive. It may be activated and it may be difficult for the cross-linking reaction of the organic cross-linking agent to proceed effectively.

In this step, the iodide can be used to maintain the uniformity of polarization in the plane of the polarizer and to prevent the desorption of dyed iodine. The iodide may be the same as that used in the dyeing step, the content of which may be 0.05 to 15% by weight with respect to 100% by weight of water, but is limited thereto. However, it may be preferably 0.5 to 11% by weight. If the content is less than 0.05% by weight, iodide ions in the film may escape and increase the transmittance of the polarizer, and if it exceeds 15% by weight, the iodide ions in the aqueous solution may be transferred 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 polarizing element forming film in the complementary color tank may be 1 second to 15 minutes, but is not limited to this, and may be preferably 5 seconds to 10 minutes.

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

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

<Stretching step>
In the present invention, the stretching step may be performed at the same time as 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 process of manufacturing the polarizer.

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

As used herein, the "cumulative draw ratio" means the value of the product of the draw ratios at each step.

<Washing step>
In the method for producing a polarizer of the present invention, if necessary, the film for forming a polarizing element, which has been crosslinked and stretched, is immersed in a washing tank filled with an aqueous solution for washing, and is used for forming a polarizer in the steps up to the washing step. It may further include a washing step to remove unwanted residues such as boric acid adhering to the film.

In the present invention, as the aqueous solution for washing, an aqueous solution for washing known in the art can be used without particular limitation, and for example, water may be used, or iodide may be further added thereto, but the present invention is limited thereto. Not done.

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

The washing step is optional and can be performed each time a step prior to the washing step, such as the dyeing step or the cross-linking step, is completed. Further, it may be repeated once or more, 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 water-washed polarizing film, and the neck-in by drying further improves the orientation of the dyed iodine molecules. This is a step of obtaining a polarizer having excellent optical characteristics. The neck-in means that the width of the film is narrowed.

The drying step according to the present invention includes a step of contacting the polarizing film for forming a film with a heat roll to dry it, and the time for contacting the film for forming a polarizer with a heat roll is 50% or more of the total drying time.

As discussed above, the present invention makes it possible to achieve the desired effect in the present invention by contacting the polarizing element forming film with a heat roll and drying it. At this time, the film can be achieved. The time of contact with the heat roll is adjusted to 50% or more of the total drying time. Specifically, the time for bringing the polarizing film into contact with the thermal roll may be 30 to 600 seconds, preferably 40 to 120 seconds, more preferably 40 to 60 seconds, and 42. It is particularly preferably ~ 58 seconds.

In the present invention, the thermal 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 execution time of the drying step, and refers to the time during which some drying method is performed on the polarizing film. For example, in the case of drying by contacting with a hot roll, the time for contacting the film with the hot roll, in the case of using a plurality of hot rolls, the time for transporting the film between the hot rolls, hot air drying may be used. For example, the time when hot air is applied to the film, the time when air is applied to the film for air drying, the time when the film is heated for heat drying, and the time when the film is irradiated with far infrared rays for far infrared drying. In the case of microwave drying, the time during which the film is irradiated with infrared rays is included in the total drying time. Therefore, the total drying time also includes a time during which a drying method other than the method of contacting the polarizing element forming film with a heat roll to dry it is performed.

In the present invention, when the time for the film for forming the polarizer to be in contact with the thermal roll is 50% or more of the total drying time, it becomes easy to manufacture a polarizer having an arithmetic mean height (Sa) of 21.0 nm or less. It is possible to reduce streak-like unevenness extending along the stretching direction with contraction force and unevenness in the absorption axis direction of the manufactured polarizing element.

In the drying step according to the present invention, the neck-in value of the polarizer can be adjusted, and for example, the drying neck-in value defined by the following formula 1 may be 10 to 15%. :
[Formula 1]
Dry neck-in = {(W1-W2) / W1} * 100 (%)
(In the formula, 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 within the above range, it can be adjusted by controlling the ratio of the thermal roll drying time to the total drying time at 50% or more.

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

In the present invention, the drying step can be accompanied by hot air drying as well as contact of the polarizer forming film with a 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 to be equal to or higher than the temperature of the hot air, for example, 5 to 20 ° C. higher. The temperature of the thermal roll is preferably 100 ° C. or lower from the viewpoint of preventing deterioration of the polarizer.

The total drying time is not particularly limited and can be carried out, 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 0 to 2 minutes, for example.

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 by bonding a polarizer protective film on at least one surface thereof.

The material of the polarizer protective film is not particularly limited, and various transparent resin films including at least one selected from the group consisting of, for example, acrylic resin films, cellulose resin films, polyolefin resin films and polyester resin films can be 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; Cellulosic resin films such as diacetylcellulose, triacetylcellulose, cellulose acetate propionate; polyolefin-based resin films having polyethylene, polypropylene, cyclo-based or norbornene structures, polyolefin-based resin films such as ethylene-propylene copolymers; and the like. 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 the polarizer protective films are laminated on both sides of the polarizer, the protective films may be the same as each other or have different thicknesses.

The binder and the polarizer protective film may be bonded by using an adhesive composition. Bonding of the polarizer and the protective film using the adhesive composition can be performed by an appropriate method, for example, casting method, Meyerbar coating method, gravure coating method, die coating method, immersion coating method, spraying method, etc. A method of applying the adhesive composition to the adhesive surface of the polarizing film and / or the protective film and superimposing both thereof can be mentioned. The casting method is a method of applying an adhesive composition to the surface of a polarizer or a protective film to be coated while moving it in a substantially vertical direction, a generally horizontal direction, or an oblique direction between the two. ..

After applying the adhesive composition, the polarizer and the protective film are sandwiched and joined by a nip roll.

Further, in order to improve the adhesiveness, surface treatments such as plasma treatment, corona treatment, ultraviolet irradiation treatment, frame treatment and saponification treatment can be appropriately performed on the surface of the polarizer and / or the protective film. Examples of the saponification treatment include a method of immersing in an alkaline aqueous solution such as sodium hydroxide and potassium hydroxide.

After laminating the polarizer and the polarizer protective film, a drying treatment is performed. The drying treatment 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 can be applied not only to a normal liquid crystal display device but also to various image display devices such as an organic electric field emission display device (OLED), a plasma display device, and a field emission display device.

Hereinafter, preferred examples will be presented to aid the understanding of the present invention, but these examples merely exemplify the present invention, do not limit the scope of the appended claims, and fall within the scope of the present invention. And it is clear to those skilled in the art that various changes and amendments to the Examples are possible within the scope of the technical idea, and it is not surprising that these changes and amendments fall within the appended claims.

<Example 1>
A transparent unstretched polyvinyl alcohol film (PE60, KURARAY) having a saponification degree of 99.9% or more was immersed in water at 25 ° C. (deionized water) for 2 minutes to swell (swelling step), and then iodine. Staining was carried out by immersing in an aqueous solution for dyeing at 30 ° C. containing 2.1% 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, in the swelling and staining steps, stretching was performed at 1.482 times and 1.607 times, respectively. Next, the mixture was immersed in an aqueous solution for cross-linking 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 (cross-linking step), and 2.266 while cross-linking. It was stretched at a double stretching ratio. Then, it was stretched 1.05 times while being 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 for 9 seconds (complementary color step).

The crosslinked polyvinyl alcohol film was washed with deionized 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%. The specific conditions for the hot roll and hot air are as shown in Table 1 below.

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

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

<Test example>
The physical properties of the polarizers and polarizing plates manufactured 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 by the above formula 1.

<2. Mura level measurement>
After manufacturing the polarizing plate, the presence or absence of visible streak-like 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 the light of a fluorescent lamp is incident from an oblique direction of about 45 ° and the unevenness of the polarizing plate is visually confirmed by the reflected light.
Lv1. : Level at which unevenness cannot be confirmed in the obtained polarizing plate Lv2. : In the obtained polarizing plate, unevenness is visible 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 the level can be visually recognized.

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

<4. Contraction force measurement>
Here, the contraction force in the absorption axis direction was measured around a width of 2 mm in the transmission axis direction of the polarizer. After cutting the polarizer produced in Examples and Comparative Examples to a size of 3.0 cm (absorption axis direction) × 2 mm (transmission axis direction), DMA Q800 (Dynamic mechanical analyzer, TA) at 80 ° C. for 4 hours. The contraction force in the absorption axis direction was measured when standing still. At this time, a minimum load was applied in the thickness direction of the polarizer in order to maintain the polarizer in a flat state before the measurement.

<5. Optical characteristics (polarization degree)>
The produced polarizer was cut into a size of 4 cm × 4 cm, and then the transmittance was measured using an ultraviolet-visible spectroscope (V-7100, manufactured by JASCO Corporation). At this time, the degree of polarization is defined by the following mathematical formula 2.
[Formula 2]
Polarization degree (P) = [(T _1- T ₂ ) / (T ₁ + T ₂ )] ^1/2
(In the equation, T ₁ is the parallel transmittance obtained when the pair of polarizers are arranged in a state where the absorption axes are parallel, and T ₂ is the case where the pair of polarizers are arranged in a state where the absorption axes are orthogonal to each other. The obtained orthogonal transmittance).

With reference to Table 2, the polarizer that has undergone the drying step of the present invention has irregularities as compared with the whole of Comparative Examples, although the degree of polarization is almost comparable to that of Comparative Examples 3 and 5 dried only with hot air. It can be confirmed that the streak-like unevenness extending along the stretching direction and the contraction force in the absorption axis direction are greatly reduced.

Claims (2)

Includes swelling, dyeing, stretching, cross-linking, complementary color, and drying steps of the polarizing film.
The dyeing, cross-linking, and complementary color steps are included in this order.
The staining solution in the staining step contains boric acid and contains boric acid.
The drying step includes a step of bringing the polarizing film to be brought into contact with a heat roll to dry it.
The time for contacting the polarizer-forming film with the heat roll is 50% or more of the total drying time.
The drying step further includes a hot air drying step.
A method for producing a polarizer, wherein the temperature of the heat roll is equal to or higher than the temperature of hot air. The method for producing a polarizer according to claim 1 , 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 (%).
(In the formula, 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).