CN108351453B - Polarizing plate and method for producing same - Google Patents

Abstract

The present invention provides a polarizing plate having an arithmetic mean height (Sa) of 21.0 nm or less.

Description

Polarizing plate and method of making the same

technical field

The present invention relates to a polarizing plate and a method for producing the same, and more particularly, to a polarizing plate having a small shrinkage force in the direction of the absorption axis (stretching) and little stripe-like unevenness extending along the stretching direction with unevenness and its production method.

Background technique

Polarizing plates used in various image display devices such as liquid crystal display devices (LCDs), electroluminescence (EL) display devices, plasma display devices (PDPs), field emission display devices (FEDs), OLEDs, etc. are generally contained in A polarizer obtained by adsorbing an iodine-based compound or a dichroic polarizing substance on a polyvinyl alcohol (PVA) film and orienting it. A multi-layer structure in which a polarizer protective film, an adhesive layer to be joined to other members, and a release film are laminated.

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

On the other hand, in order to impart a polarizing function to a polarizing plate, a stretching process is generally required, but there is a problem that it deforms during use due to the inherent shrinkage force in the stretching (absorption axis) direction after being manufactured. Deformation of the polarizing plate causes degradation of the optical function of the polarizing plate and failure of the image display device.

In addition, in the stretching process, there is also a problem that stripe-like unevenness along the stretching direction is generated in the polarizing plate with unevenness.

Japanese Laid-Open Patent Publication No. 2010-145866 discloses a method for producing a polarizing plate with a small excessive shrinkage stress, but a satisfactory alternative to the above-mentioned problem cannot be proposed.

prior art literature

Patent Literature

Patent Document 1: Japanese Patent Laid-Open No. 2010-145866

SUMMARY OF THE INVENTION

The problem to be solved by the invention

An object of the present invention is to provide a polarizing plate with a small shrinkage force in the absorption axis direction and a method for producing the same.

Another object of the present invention is to provide a polarizing plate and a method for producing the same in which stripe-like unevenness with unevenness extending in the stretching direction is reduced.

method used to solve the problem

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

2. The polarizing plate according to 1 above, wherein the thickness is 5 to 30 μm.

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

4. A method for producing a polarizer comprising the steps of swelling, dyeing, stretching, crosslinking, and drying of a film for forming a polarizer,

The drying step includes the step of drying the film for forming a polarizer by contacting a heated roll,

The time in which the film for forming a polarizing plate is brought into contact with the heated roll is 50% or more of the total drying time.

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

6. The method for producing a polarizing plate according to 5 above, wherein the temperature of the heat roller is equal to or higher than the temperature of hot air.

7. The method for producing a polarizing plate according to any one of 4 to 6 above, wherein the dry neck-in value defined by the following mathematical formula 1 is 10 to 15%:

[Mathematical formula 1]

Drying neck-in={(W1-W2)/W1}×100(%).

(In the formula, W1 is the width of the film for forming a polarizer before the drying step, and W2 is the width of the film for forming a polarizer after the drying step).

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

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

Invention effect

The polarizing plate of the present invention has a low arithmetic mean height, thereby exhibiting low shrinkage force in the absorption axis direction, and can significantly reduce stripe-like unevenness extending along the stretching direction accompanied by unevenness.

In the method for producing a polarizing plate of the present invention, the film for forming a polarizing plate is dried in contact with a hot roll for a specific period of time, thereby adjusting the drying shrinkage value to a specific range, and it is possible to manufacture a film exhibiting low shrinkage in the absorption axis direction. The polarizing plate in which the force and the stripe-like unevenness extending along the stretching direction with unevenness were significantly reduced.

Detailed ways

The present invention relates to a polarizing plate, which has an arithmetic mean height (Sa) of 21.0 nm or less, and thereby has a low shrinkage force in the absorption axis direction, and a stripe-like stripe extending along the stretching direction with unevenness. The occurrence of unevenness is reduced.

Hereinafter, the present invention will be described in detail.

Generally, a polarizer produced by stretching a film for forming a polarizer shrinks during drying during the production process, and excessive drying shrinkage occurs during such shrinkage, resulting in unevenness along the stretching direction. The problem of extended streak-like unevenness. In addition, when the polarizing plate subsequently used in an image display device or the like is heated from the outside, the shrinkage force in the absorption axis direction which cannot be sufficiently eliminated appears, and there is a problem that the polarizing plate is deformed.

Therefore, by adjusting the arithmetic mean height (Sa) of the polarizing plate of the present invention to 21.0 nm or less, the shrinkage force in the absorption axis direction and the stripe-like unevenness extending along the stretching direction with unevenness can be significantly reduced.

The inventors of the present invention control the shrinkage in the width direction (direction perpendicular to the stretching direction) of the polarizer by supporting the film for forming a polarizer with a hot roller when the film for forming a polarizer is brought into contact with a hot roller to be dried. Since unevenness caused by deformation of the polarizing plate in the width direction is suppressed, stripe-like unevenness that extends along the stretching direction along with the unevenness is suppressed. In addition, by controlling the shrinkage in the width direction of the polarizer, the thickness of the film for forming a polarizer is further reduced to such an extent that the shrinkage force in the stretching (absorption axis) direction of the polarizer is reduced. Although it is judged as mentioned above, it is not limited to this interpretation.

In addition, the inventors of the present invention adjusted the arithmetic mean height (Sa) of the polarizing plate to be 21.0 nm or less, reduced the shrinkage force in the absorption axis direction, and made the streak-like unevenness extending along the stretching direction with unevenness to be conspicuous reduce. As long as the arithmetic mean height of the polarizing plate is 21.0 nm or less, the intended effect of the present invention can be achieved, so the lower limit is not particularly limited, and may be, for example, 1.0 nm or more, or 0.1 nm or more, or more than 0 nm. The arithmetic mean height of the polarizing plate 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 mean height (Sa) can be determined based on ISO 25178, for example. In the present invention, in order to adjust the arithmetic mean height (Sa) of the polarizing plate 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.

The polarizing plate of the present invention whose arithmetic mean height is adjusted can have a relatively low thickness compared with ordinary polarizing plates, and from these viewpoints, the lower limit of the thickness of the polarizing plate may be 5 μm or 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 polarizing plate to the said range, it can adjust by controlling the ratio of the heat roll drying time in the whole drying time to 50% or more.

On the other hand, the polarizing plate of the present invention has a low shrinkage force in the absorption axis direction as described above, for example, the shrinkage 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. Since the shrinkage force in the absorption axis direction is as low as possible, the lower limit thereof is not particularly limited, but 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 this invention, in order to adjust the shrinkage force of a polarizing plate to the said range, it can adjust by controlling the ratio of the heat roll drying time in the total drying time to 50% or more.

Moreover, this invention provides the manufacturing method of the said polarizing plate.

The manufacturing method of the polarizer of the present invention includes the steps of swelling, dyeing, stretching, cross-linking and drying of the film for forming a polarizer, wherein the drying step includes a step of drying the film for forming a polarizer by contacting a hot roller, and drying the film for forming a polarizer. The time that the film for polarizing plate formation is in contact with the hot roll is 50% or more of the total drying time.

If the manufacturing method of the polarizing plate of this invention is demonstrated more concretely, it will be as follows.

The polarizing plate-forming film used for the production of polarizing plates can be used without particular limitation as long as it is a polymer film used for the production of polarizing plates, a film that can be dyed with a dichroic substance (for example, iodine) well-known in the field For example, polyvinyl alcohol films, partially saponified polyvinyl alcohol films; polyethylene terephthalate films, ethylene-vinyl acetate copolymer films, ethylene-vinyl alcohol copolymer films, cellulose Hydrophilic polymer films such as films, their partially saponified films, etc.; or polyolefin orientations such as dehydration-treated polyvinyl alcohol-based films, dehydrochloric acid-treated polyvinyl chloride-based films, etc. film; etc. Among them, a polyvinyl alcohol-based film is preferable because it is excellent not only in the effect of enhancing the uniformity of the degree of polarization in the plane, but also in the dyeing affinity to iodine.

The manufacturing method of the polarizer of the present invention may include a swelling step, a dyeing step, a cross-linking step, a color correction step, a stretching step, a water washing step, and a drying step, and can be classified by the stretching method. For example, a dry stretching method, a wet stretching method, or a mixed stretching method in which the two types of stretching methods are mixed may be mentioned. Hereinafter, although the manufacturing method of the polarizing plate of this invention is demonstrated using the wet stretching method as an example, it is not limited to this.

The remaining steps other than the drying step in the above steps can be carried out in a state of immersing the film for forming a polarizer in a constant temperature bath filled with one or more kinds of solutions selected from various solutions.

<Swelling step>

The swelling step is a step of immersing the unstretched film for forming a polarizer in a swelling tank filled with an aqueous solution for swelling before dyeing the unstretched film for forming a polarizer to remove dust deposited on the surface of the film for forming a polarizer. Or impurities such as anti-blocking agents, swell the film for forming polarizers, improve stretching efficiency, prevent uneven dyeing, and improve the physical properties of polarizers.

As the aqueous solution for swelling, any known aqueous solution for swelling can be used without particular limitation. For example, water (pure water, deionized water) can be used alone, and when a small amount of glycerin or potassium iodide is added thereto, it can be used at a high level. While the molecular film swells, it also improves workability. 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, and may be 20 to 45°C, for example, 25 to 40°C.

The execution time of the swelling step (swelling tank immersion time) may be any known execution time in this field 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, swelling can be suppressed from reaching a saturated state excessively, breakage due to softening of the film for forming a polarizer can be prevented, iodine adsorption in the dyeing step can be uniform, and the degree of polarization can be improved.

The stretching step may be performed simultaneously with the swelling step, and at this time, the stretching ratio may be about 1.1 to 3.5 times without limitation, and may preferably be 1.3 to 3.0 times. If the stretching ratio is less than 1.1 times, wrinkles may be generated, and if it is more than 3.5 times, the initial optical characteristics may become weak.

<Dyeing step>

The dyeing step is a step of immersing the film for forming a polarizer in a dyeing tank filled with an aqueous solution for dyeing containing a dichroic substance such as iodine, and allowing the film for forming a polarizer to adsorb iodine.

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

In order to improve the dyeing efficiency, the aqueous solution for dyeing may further contain iodide as a dissolution aid. As the iodide, any known iodide in this field can be used without limitation, and for example, it can contain potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, iodide At least one of barium, calcium iodide, tin iodide, and titanium iodide, among them, potassium iodide is preferred because of its high solubility in water. The content of the iodide may be 0.01 to 10 wt % with respect to 100 wt % of water, but is not limited, and may preferably be 0.1 to 5 wt %.

In addition, in order to increase the content of the iodine complex in the film for polarizing plate formation, boric acid may be added to the dyeing tank in an amount of 0.3 to 5 wt % with respect to 100 wt % of water, but it is not limited to this. When the boric acid in the dyeing tank is less than 0.3 wt %, there is a possibility that there is no effect on the increase of the content of PVA ^- I ₃ -complex and PVA ^- I ₅ -complex, and the boric acid in the dyeing tank is more than 5 wt % At the concentration of , the risk of membrane rupture 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 polarizer formation in a dyeing tank is not specifically limited, It may be 1 to 20 minutes, Preferably it may be 2 to 10 minutes.

In the present invention, the stretching step may be performed simultaneously with the dyeing step, and in this case, the stretching ratio may be 1.01 to 2.0 times, but is not limited thereto, and may preferably be 1.1 to 1.8 times.

In addition, 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 stretch ratio is less than 1.2 times, wrinkles of the film may occur, resulting in poor appearance, and if it is greater than 4.0 times, the initial optical properties may become weak.

<Crosslinking step>

In the cross-linking step, the dyed film for forming a polarizer is immersed in an aqueous solution for cross-linking so that the dyeability due to the physically adsorbed iodine molecules does not decrease due to the external environment, and the adsorbed iodine molecules are fixed. step.

When the crosslinking reaction of iodine, which is a dichroic dye, is insufficient, the iodine molecules are desorbed by the moist heat environment, and thus a sufficient crosslinking reaction is required. In addition, in order to orient the iodine molecules located between the molecules of the polarizing plate-forming film and improve the optical properties, stretching may be performed at the maximum stretching ratio in the crosslinking step.

In the present invention, a method for producing a polarizer can use a cross-linking step known in the field without particular limitation. In one or more of the linking steps, an aqueous solution for crosslinking containing a boron compound can be used. Thereby, the optical properties and color durability of the polarizing plate can be improved.

The cross-linking aqueous solution can be used without particular limitation in the cross-linking aqueous solution known in the field, for example, it may contain water as a solvent, and boron compounds such as boric acid or sodium borate, and may also contain mutually soluble organic compounds together with water. Solvents and iodides.

The boron compound imparts a short crosslinking bond and rigidity to the polarizer, suppresses the generation of wrinkles in the film during the process, improves the handleability of the film, and acts to form the iodine orientation of the polarizer.

The content of the boron compound can be a content known in the art, for example, it can be 1 to 10 wt % relative to 100 wt % of water, preferably 2 to 6 wt %. When the content is less than 1% by weight, the crosslinking effect of the boron compound is reduced, and it becomes difficult to impart rigidity to the polarizer, and when the content exceeds 10% by weight, the crosslinking reaction of the inorganic crosslinking agent is excessively activated, resulting in It is difficult to efficiently advance the crosslinking reaction of the organic crosslinking agent.

In this step, iodide may be used in order to maintain the uniformity of the degree of polarization in the plane of the polarizer and to prevent desorption of the dyed iodine. The iodide may be the same as the iodide used in the dyeing step, and its content may be 0.05 to 15 wt % with respect to 100 wt % of water, without limitation, may preferably be 0.5 to 11 wt %. If the content is less than 0.05% by weight, the iodide ions in the film may be detached and the transmittance of the polarizer may increase. When the content exceeds 15% by weight, the iodide ions in the aqueous solution may permeate into the film and cause the polarizer. Transmittance decreases.

In the present invention, the temperature of the crosslinking tank may be 20 to 70°C, but is not limited thereto. Although the immersion time of the film for polarizer formation in the said crosslinking tank may be 1 second to 15 minutes, it is not limited to this, It may be preferably 5 seconds to 10 minutes.

The stretching step may be performed simultaneously 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, and may preferably be 1.5 to 2.5 times.

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

In addition, the cumulative stretching ratio of the first and second crosslinking steps may be 1.5 to 5.0 times, but is not limited thereto, and may preferably be 1.7 to 4.5 times. If the cumulative stretching ratio is less than 1.5 times, the orientation effect of iodine may become insufficient, and when it is more than 5.0 times, film breakage may occur due to excessive stretching, and productivity may decrease.

＜Complementary color step＞

The manufacturing method of the polarizing plate of the present invention may further include a complementary color step as required. The color-compensating step can stabilize the iodine complex by aligning the iodine complex between molecules in the film for forming a polarizer to which the iodine complex is physically adsorbed so as to be close to the crosslinking of boric acid. In addition, by the color correction step, the color of the film for forming a polarizer in which the dyeing of the iodine complex in the crosslinking step is insufficient can be corrected.

The color-compensating aqueous solution in the color-compensating step contains, for example, water as a solvent and a boron compound such as boric acid, and may further contain a mutually soluble organic solvent and iodide together with water.

In the present invention, the boron compound imparts a short crosslinking bond and rigidity to the polarizer, suppresses the generation of wrinkles in the film during the process, improves the handleability of the film, and can play a role in forming the iodine orientation of the polarizer.

The content of the boron compound may be 1 to 10 wt % with respect to 100 wt % of water, but is not limited thereto, and may preferably be 2 to 6 wt %. When the content is less than 1% by weight, the crosslinking effect of the boron compound is reduced, and it becomes difficult to impart rigidity to the polarizer, and when the content exceeds 10% by weight, the crosslinking reaction of the inorganic crosslinking agent is excessively activated, resulting in It is difficult to efficiently advance the crosslinking reaction of the organic crosslinking agent.

In this step, iodide may be used in order to maintain the uniformity of the degree of polarization in the plane of the polarizer and to prevent desorption of the dyed iodine. The iodide may be the same as the iodide used in the dyeing step, and its content may be 0.05 to 15 wt % relative to 100 wt % of water, but it is not limited to this, and may preferably be 0.5 to 11 wt % %. If the content is less than 0.05% by weight, the iodide ions in the film may be detached and the transmittance of the polarizer may increase. When the content exceeds 15% by weight, the iodide ions in the aqueous solution may permeate into the film and cause the polarizer. Transmittance decreases.

In the present invention, the temperature of the color correction tank may be 20 to 70°C. Although the immersion time of the film for polarizer formation in a color correction tank may be 1 second to 15 minutes, it is not limited to this, It may be preferably 5 seconds to 10 minutes.

The stretching step may be carried out simultaneously with the color-complementing step, and in this case, the stretching ratio of the color-compensating step may be 1.01 to 1.1 times, but is not limited thereto, and may preferably be 1.02 to 1.08 times.

If the stretching ratio is less than 1.01 times, the stabilization effect of the iodine complex may become insufficient, and if it exceeds 1.1 times, the film may be broken due to excessive stretching, and the productivity may be deteriorated. reduce.

<Stretching step>

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

In addition, the stretching step may be performed at least once, or may be performed multiple times. In the case of carrying out a plurality of times, it may be carried out separately in arbitrary steps in the manufacturing process of the polarizing plate.

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

In this specification, the "cumulative draw ratio" refers to the value of the product of the draw ratios in each step.

＜Water washing step＞

The method for producing a polarizer of the present invention may further include, if necessary, a water washing step of immersing the film for forming a polarizer after crosslinking and stretching in a water washing tank filled with an aqueous solution for washing, and removing the water washing. Unwanted residues such as boric acid adhering to the film for polarizing plate formation in the step before the step.

In the present invention, the water-washing aqueous solution known in the art can be used without particular limitation. For example, it may be water or iodide may be added thereto, but it is not limited to these.

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

The water washing step may be omitted, or may be performed at the end of each step before the water washing step such as the dyeing step or the crosslinking step. In addition, 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 film for forming a polarizer, and further improving the orientation of the dyed iodine molecules by neck-in due to drying to obtain an optical Steps for polarizers with excellent properties. In addition, the narrowing means that the width|variety of a film becomes narrow.

The drying step of the present invention includes a step of drying the film for forming a polarizing plate by contacting the film for forming a polarizing plate with a heating roller, and the time during which the film for forming a polarizing plate is brought into contact with the heating roller is 50% or more of the total drying time.

As shown in the above study, the present invention can achieve the intended effect of the present invention by contacting the film for polarizing plate formation with the heated roller and drying, and in this case, the time for the film to be brought into contact with the heated roller is adjusted to 50% of the total drying time above. Specifically, the time during which the film for forming a polarizing plate is brought into contact with the heat roll may be 30 to 600 seconds, preferably 40 to 120 seconds, more preferably 40 to 60 seconds, and particularly preferably 42 to 58 seconds.

In the present invention, the heat roll refers to a roll heated at a temperature higher than the surrounding temperature. For example, the heat roller may have a temperature higher than the ambient temperature by about 5 to 20°C. The number of heat rolls may be one or a plurality of them may be used.

In the present invention, the total drying time refers to the execution time of the drying step, and refers to the time during which a certain drying method is performed on the film for forming a polarizer. For example, if drying is carried out by contacting a heated roll, the total drying time includes the time when the film is brought into contact with the heated roll, and in the case of using a plurality of heated rolls, the time for conveying the film between the heated rolls is included. Time, in the case of hot air drying, the time of blowing hot air to the film is included in the total drying time, and the time of blowing air to the film in the case of air drying is included in the total drying time, and the heating film is included in the total drying time in the case of heat drying. In the case of far-infrared drying, the time for irradiating the film with far-infrared rays is included in the total drying time, and in the case of microwave drying, the time for irradiating the film with microwaves is included in the total drying time. Therefore, the time which performs the drying method other than the method of making the film for polarizing plate formation contact a hot roll and drying is also included in all drying time.

In the present invention, when the time during which the film for forming a polarizer is in contact with the heat roll is 50% or more of the total drying time, it is easy to manufacture a polarizer having an arithmetic mean height (Sa) of 21.0 nm or less, and the number of polarizers to be manufactured can be reduced. It absorbs the shrinkage force in the axial direction and the stripe-like unevenness that extends along the stretching direction with the unevenness.

In the drying step of the present invention, the neck-in value of the polarizer can be adjusted, for example, the drying neck-in value defined by the following mathematical formula 1 can be 10 to 15%:

[Mathematical formula 1]

Drying shrinkage={(W1－W2)/W1}×100(%)

(In the formula, W1 is the width of the film for forming a polarizer before the drying step, and W2 is the width of the film for forming a polarizer after the drying step).

In the present invention, in order to adjust the drying shrinkage value of the polarizing plate 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 drying neck-in value is in the above-mentioned range, the shrinkage force in the absorption axis direction and the effect of reducing unevenness in the stretching direction can be more significantly reduced.

In the present invention, the drying step may be performed in parallel with hot air drying while the film for forming a polarizing plate is in contact with the heat roll. At this time, the temperature of the hot air can be, for example, 20 to 100° C., and the temperature of the heat roller can be set to be higher than the temperature of the hot air, for example, 5 to 20° C. high. From the viewpoint of preventing deterioration of the polarizing plate, the temperature of the heat roll is preferably 100° C. or lower.

The total drying time is not particularly limited, and for example, 1 to 10 minutes can be carried out. The drying time by hot air among the whole drying time is not particularly limited, and for example, it can be carried out for 0 to 2 minutes.

In the present invention, other than hot air drying, drying methods known in the field may be used in combination without limitation. For example, methods such as air drying, heating drying, far-infrared drying, and microwave drying may be used.

The polarizing plate of the present invention can be provided as a polarizing plate by bonding a polarizing plate protective film to at least one surface.

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

Specific examples of the protective film include acrylic resin films such as polymethyl (meth)acrylate and polyethyl (meth)acrylate; polyethylene terephthalate, polyethylene isophthalate Polyester resin films such as ethylene formate, polyethylene naphthalate, polybutylene terephthalate, etc.; diacetyl cellulose, triacetyl cellulose, cellulose acetate propionate, etc. Cellulose-based resin films; polyethylene, polypropylene, polyolefin-based resin films having a cyclic or norbornene structure, polyolefin-based resin films such as ethylene-propylene copolymers; etc., but not limited to them.

The thickness of the protective film is not particularly limited, and may be 10 to 200 μm, preferably 10 to 150 μm. When polarizing plate protective films are laminated on both surfaces of the polarizing plate, each protective film may have the same or different thicknesses from each other.

The bonding of the polarizer and the polarizer protective film can be carried out using an adhesive composition. The bonding of the polarizer and the protective film using the adhesive composition can be carried out by an appropriate method, for example, by a casting method, a Meyer bar coating method, a gravure coating method, a die coating method, and a dip coating method. A method of applying an adhesive composition to the adhesive surface of a polarizing film and/or a protective film, such as a method or a spray method, and stacking the two. The so-called casting method is a method of applying an adhesive composition to the surface of a polarizer or a protective film, which is an object to be coated, while moving a polarizer or a protective film in a substantially vertical direction, a substantially horizontal direction, or an oblique direction between the two. method.

After applying the adhesive composition, the polarizing plate and the protective film were sandwiched and joined by a nip roll.

In addition, in order to improve the adhesiveness, surface treatments such as plasma treatment, corona treatment, ultraviolet irradiation treatment, flame treatment, and saponification treatment may be appropriately performed on the surface of the polarizer and/or the protective film. As the saponification treatment, a method of immersing in an aqueous solution of an alkali such as sodium hydroxide or potassium hydroxide can be mentioned.

The drying process is performed after laminating|stacking a polarizer and a polarizer protective film. The drying process can be performed by, for example, spraying hot air, and the temperature at this time can be appropriately selected in the range of 50 to 100 degrees. The drying time is usually 30 to 1000 seconds.

The polarizing plate of the present invention can be applied not only to ordinary liquid crystal display devices, but also to various image display devices such as organic electroluminescence display devices (OLED), plasma display devices, and field emission display devices.

Hereinafter, preferred examples are given to facilitate understanding of the present invention, but these examples are merely examples for illustrating the present invention, and are not intended to limit the scope of additional technical solutions, and those skilled in the art may It is clear that various changes and corrections can be made to the embodiments within the scope of the present invention and the scope of the technical idea, and these changes and corrections naturally belong to the scope of the claims of the present invention.

<Example 1>

A transparent unstretched polyvinyl alcohol film (PE60, KURARAY) having a degree of saponification of 99.9% or more was immersed in water (deionized water) at 25°C for 2 minutes to swell (swelling step), Dyeing was performed by immersing in 2.0 mM/L of iodine and an aqueous solution for dyeing at 30°C containing 1.1 wt % of potassium iodide and 0.3 wt % of boric acid with respect to 100 wt % of water for 2 minutes and 14 seconds (dyeing step). At this time, in the swelling and dyeing steps, stretching was performed at a stretching ratio of 1.482 times and 1.607 times, respectively. Then, it was immersed in an aqueous solution for crosslinking at 53° C. containing 11.0 wt % of potassium iodide and 4 wt % of boric acid with respect to 100 wt % of water to be cross-linked by dipping for 39 seconds (cross-linking step), and then stretched by 2.266 times. than stretched. Then, it stretched by 1.05 times while being immersed for 9 seconds in an aqueous solution for color correction containing 11% by weight of potassium iodide and 4% by weight of boric acid relative to 100% by weight of water at 40°C (color correction 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 polarizing plate with a transmittance of 42.5%. The specific conditions of the hot roll and hot air are as described in Table 1 below.

A triacetyl cellulose (TAC) film was laminated|stacked on both surfaces of the produced polarizing plate, and a polarizing plate was produced.

<Examples 2 to 9 and Comparative Examples 1 to 5>

A polarizing plate was manufactured by the same method as Example 1 except having adjusted each temperature and drying time of a hot roll and a hot air as described in the following Table 1.

[Table 1]

[Table 1]

<Test example>

The physical properties of the polarizing plates and polarizing plates produced in the above-mentioned Examples and Comparative Examples were measured by the following methods, and the results are shown in Table 2 below.

<1. Measurement of drying narrowing>

Dry neck-in, which means the ratio of the reduction before and after drying of the polarizing plate, was measured by the above-mentioned formula 1.

<2. Measurement of uneven level>

After the production of the polarizing plate, it was visually checked by the fluorescent lamp reflection method according to the following criteria whether or not stripe-like unevenness extending in the stretching direction accompanied by unevenness was observed. The fluorescent lamp reflection method is an evaluation method for visually confirming the unevenness of the polarizing plate by the reflected light of light incident on the fluorescent lamp from an oblique direction of about 45°.

Lv1.: Uneven level was not confirmed in the obtained polarizing plate

Lv2.: In the obtained polarizing plate, the unevenness was observed by the fluorescent lamp reflection method, but the unevenness was not visually observed.

Lv3.: In the obtained polarizing plate, unevenness can be observed by a fluorescent lamp reflection method, and unevenness can be observed visually

<3. Measurement of the arithmetic mean height (Sa) of the PVA surface>

After cutting the manufactured polarizing plate into a size of 1 cm×1 cm, the arithmetic mean height in the plane of the polarizing plate was measured based on ISO 25178-2 using a surface interferometer (ZYGO, manufactured by MetroPro).

<4. Measurement of contractile force>

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

<5. Optical characteristics (degree of polarization)>

After cutting the produced polarizing plate into a size of 4 cm×4 cm, the transmittance was measured using an ultraviolet-visible ray spectrometer (V-7100, manufactured by JASCO Corporation). At this time, the degree of polarization is defined by the following equation 2.

[Mathematical formula 2]

Degree of polarization (P)=[(T ₁ -T ₂ )/(T ₁ +T ₂ )] ^1/2

(In the _formula , T1 is the parallel transmittance obtained when _a pair of polarizers are arranged in a state where the absorption axes are parallel, and T2 is the orthogonal transmittance obtained when a pair of polarizers are arranged in a state where the absorption axes are orthogonal) .

[Table 2]

[Table 2]

Referring to Table 2, it can be confirmed that the polarizing plate of the present invention that has undergone the drying step is basically not inferior to the degree of polarization of Comparative Examples 3 and 5 dried only by hot air, but is accompanied by unevenness compared with all the Comparative Examples. The streak-like unevenness extending in the stretching direction and the shrinkage force in the absorption axis direction are greatly reduced.

Claims (2)

1. A method for manufacturing a polarizing plate is provided,

the manufacturing method comprises the steps of swelling, dyeing, stretching, crosslinking and drying of the film for forming the polarizing plate,

the drying step includes a step of drying the polarizer-forming film by contacting it with a heat roll,

the time for which the polarizing plate-forming film is brought into contact with a hot roll is 50% or more of the total drying time,

the drying step further comprises a hot air drying step,

The temperature of the hot roll is set to be 5 to 20 ℃ higher than the temperature of the hot air.

2. The polarizing plate production method according to claim 1, wherein,

the drying shrinkage value defined by the following mathematical formula 1 is 10% to 15%:

dry neck-in { (W1-W2)/W1 } × 100 (%) equation 1

In the formula, W1 represents the width of the polarizing plate-forming film before the drying step, and W2 represents the width of the polarizing plate-forming film after the drying step.