TWI762455B - Polarizer and method for manufacturing thereof - Google Patents

Abstract

The present invention relates to a polarizer whose arithmetic average height (Sa) is 21.0 nm or less.

Description

Polarizer and method of making the same

The present invention relates to a polarizer and a method for producing the same, and more specifically, relates to a polarizer with low shrinkage force in the direction of the absorption axis (extending) and less streaks extending in the extending direction accompanied by unevenness and a method for producing the same.

It is used in various image display devices such as liquid crystal display device (LCD), electroluminescence (EL) display device, plasma display device (PDP), field emission display device (FED), organic electroluminescence display device (OLED), etc. Polarizers generally contain polarizers that absorb aligned iodine compounds or dichroic polarizers in a polyvinyl alcohol (PVA) film. A polarizer protective film is sequentially laminated on one side of the polarizer. On the other side of the polarizer, a multi-layer structure of a polarizer protective film, an adhesive layer bonded with other components, and a release film is sequentially laminated.

The polarizer constituting the polarizing plate is used in an image display device, and it is basically required to have both high transmittance and polarization degree in order to provide an image with excellent color reproducibility. In order to achieve these requirements, the polyvinyl alcohol-based film itself is modified, or the non-sublimation dichroic dye is used instead of sublimation. A polarizer is produced by the method of a specific iodine-based polarizer.

On the other hand, in general, a polarizer must have an extension step in order to impart a polarizing function, but there is a problem of deformation during use due to the shrinkage force in the extension (absorption axis) direction after manufacture. Deformation of the polarizer can lead to a decrease in the optical function of the polarizer and failure of the image display device.

In addition, in the extending step, the polarizer also has a problem of stripe-like irregularities extending along the extending direction along with the unevenness.

Japanese Laid-Open Patent Publication No. 2010-145866 discloses a method for producing a polarizer with low shrinkage stress, but does not suggest an alternative solution that satisfies the above problems.

[Prior Art Literature] [Patent Literature]

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

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

Furthermore, another object of the present invention is to provide a polarizer in which streak-like irregularities extending in the extending direction with unevenness are reduced, and a method for producing the same.

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

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

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

4. A manufacturing method of a polarizer, comprising: swelling, dyeing, stretching, cross-linking, and drying steps of the polarizer-forming film, wherein the aforementioned drying step includes drying the polarizer-forming film in contact with a hot roller. step, the contact time of the film for forming a polarizer with the heat roller is set to be more than 50% 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. The method for producing a polarizer according to 5 above, wherein the temperature of the heat roller is higher than the temperature of the hot air.

7. The manufacturing method of the polarizer described in any one of the above 4 to 6, the dry neck-in (neck-in) value defined by the following mathematical formula 1 is 10 to 15%: [Mathematical formula 1] dry 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 polarizer according to any one of 1 to 3 above, and a protective film bonded to at least one surface of the polarizer.

9. An image display device comprising the above-mentioned 8 loaded polarizer.

Since the polarizer of the present invention has a low arithmetic mean height and exhibits a low shrinkage force in the direction of the absorption axis, it is possible to remarkably reduce the streak-like irregularities extending in the extending direction accompanying the unevenness.

In the method for producing a polarizer of the present invention, by drying the film for forming a polarizer in contact with a hot roller for a specific period of time, and adjusting the drying shrinkage value within a specific range, it is possible to produce a low shrinkage in the direction of the absorption axis. A polarizer that significantly reduces the streaks that extend along the extending direction along with the concavities and convexities.

The present invention relates to a polarizer and a method for producing the polarizer which reduces the occurrence of streaks extending in the extending direction due to unevenness due to low shrinkage force in the absorption axis direction due to the arithmetic mean height (Sa) of 21.0 nm or less.

Hereinafter, the present invention will be described in detail.

In general, polarizers manufactured from stretched polarizer-forming films shrink during drying during the manufacturing process. However, during such shrinkage, excessive drying shrinkage occurs, and unevenness may occur along the extending direction. Extended streak problem. In addition, the shrinking force in the absorption axis direction which cannot be sufficiently relieved will be manifested when the polarizer is heated from the outside when it is used in image display devices and the like, which causes the problem of deformation of the polarizer.

Here, by adjusting the arithmetic mean height (Sa) of the polarizer of the present invention to be 21.0 nm or less, the shrinking force in the absorption axis direction and the streak-like irregularities extending in the extending direction accompanied by unevenness can be significantly reduced.

The inventors of the present invention control the width direction (direction perpendicular to the extending direction) of the polarizer by controlling the polarizer forming film to be supported by the heating roller when the film for forming a polarizer is brought into contact with a heating roller to dry it. ) shrinkage, suppresses the concavo-convex phenomenon caused by the deformation of the polarizer in the width direction, thereby suppressing the streak-like irregularities extending along the extending direction accompanying the concavo-convex. In addition, by suppressing the shrinkage in the width direction of the polarizer, the thickness of the film for forming a polarizer is further reduced only at this portion, thereby reducing the shrinkage force in the extension (absorption axis) direction of the polarizer. Although it is judged as mentioned above, it is not limited to such an interpretation.

In addition, the inventors of the present invention adjusted the arithmetic mean height (Sa) of the polarizer to 21.0 nm or less, thereby reducing the shrinkage force in the absorption axis direction, and significantly reducing streak-like irregularities extending in the extending direction accompanied by unevenness. If the arithmetic mean height of the polarizer is 21.0 nm or less, the lower limit is not particularly limited in order to achieve the effect of the object of the present invention. Although the arithmetic mean height of the polarizer may be 21.0 nm or less, it is preferably 19.0 nm or less, and more preferably 17.0 nm or less. The arithmetic mean height (Sa) can be determined according to ISO 25178, for example. 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 heating roller drying time to 50% or more in the total drying time.

The polarizer of the present invention whose arithmetic mean height has been adjusted, The thickness of the polarizer may be relatively lower than that of a normal polarizer, and the lower limit of the thickness of the polarizer on the side surface 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 the present invention, in order to adjust the thickness of the polarizer within the above-mentioned range, it can be adjusted by controlling the ratio of the heating roller drying time to 50% or more in the total drying time.

On the other hand, the polarizer of the present invention has the aforementioned low shrinkage force in the absorption axis direction, 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 is not particularly limited. In the present invention, in order to adjust the shrinkage force of the polarizer within the above-mentioned range, it can be adjusted by controlling the ratio of the heating roller drying time to 50% or more in the total drying time.

Moreover, this invention provides the manufacturing method of the said polarizer.

The manufacturing method of the polarizer of the present invention includes the steps of swelling, dyeing, extending, cross-linking and drying of the film for forming a polarizer. 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.

The manufacturing method of the polarizer of this invention is demonstrated more concretely as follows.

Polarizer-forming films for the manufacture of polarizers, only As long as it is a polymer film that can be used in the manufacture of polarizing plates, a film that can be dyed by a dichroic substance (eg, iodine) known in the field can be used without particular limitation, for example, polyvinyl alcohol can be used Films, partially saponified polyvinyl alcohol films; polyethylene terephthalate films, ethylene-ethyl acetate copolymer films, ethylene-vinyl alcohol copolymer films, cellulose films, partially saponified films of these, etc. Hydrophilic polymer films; or polyene oriented films such as polyvinyl alcohol-based films subjected to dehydration treatment, polyvinyl chloride-based films subjected to dehydrochloric acid treatment, and the like. Among them, the polyvinyl alcohol-based film is preferred from the viewpoint of not only the effect of enhancing the uniformity of the degree of polarization in the plane, but also the dyeing affinity with iodine.

According to the manufacturing method of the polarizer of the present invention, a swelling step, a dyeing step, a cross-linking step, a color correction step, an extension step, a water washing step and a drying step may be included. It can be classified by the stretching method, for example, a dry stretching method, a wet stretching method, or a hybrid stretching method in which the above-mentioned two types of stretching methods are mixed, etc. are mentioned. Hereinafter, the method for manufacturing the polarizer of the present invention will be described by taking the wet stretching method as an example, but it is not limited thereto.

Among the above-mentioned steps, the remaining steps except the drying step may be immersed in a constant temperature water bath (bath) filled with one or more solutions selected from various types of solutions to immerse the film for polarizer formation status is carried out.

<swelling step>

In the swelling step, the unstretched polarizer-forming film is immersed in a swelling tank filled with an aqueous solution for swelling before dyeing, and the accumulated polarized light is removed. Dust or impurities such as clogging inhibitors on the surface of the film for forming the film, and swelling the film for forming the polarizer, improve the stretching efficiency, and prevent the non-uniformity of dyeing, which is a step for improving the physical properties of the polarizer.

As the swelling aqueous solution, any known swelling solution in the field can be used without particular limitation. For example, water (pure water, deionized water) may be used alone, and a small amount of glycerol or potassium iodide may be added to it. It can also improve processability while swelling with 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 (swelling tank immersion time) can be applied without any particular limitation by applying the execution time known in this field, and may be, for example, 180 seconds or less, preferably 150 seconds or less. When the immersion time is within the above range, swelling can be suppressed from becoming an oversaturated state, cracking can be prevented by softening the film for forming polarizers, iodine adsorption can be made uniform in the dyeing step, 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 also be about 1.1 to 3.5 times but not limited, and preferably 1.3 to 3.0 times. Wrinkles may occur when the aforementioned elongation ratio is less than 1.1 times, and when it exceeds 3.5 times, the initial optical properties may become weak.

<Dyeing step>

In the dyeing step, the polarizer-forming film is immersed in a dyeing tank filled with an aqueous solution for dyeing containing dichroic substances such as iodine, and the polarizer-forming film is immersed in a dyeing tank. The step of absorbing iodine on the prepared film.

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

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

In addition, in order to increase the content of the iodine complex in the polarizer-forming film, 0.3 to 5 wt % of boric acid may be added to 100 wt % of water in the dyeing tank, but it is not limited thereto. When the boric acid concentration in the dyeing tank is less than 0.3 wt%, the increase of the content of PVA ^- I ₃ -complex and PVA ^- I ₅ -complex may have no effect. There is a possibility that the risk will increase.

The temperature of the dyeing tank may be 5 to 42°C, but not limited thereto, and may preferably be 10 to 35°C. In addition, 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, it can be 2 to 10 minutes.

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

In addition, the extension ratio including the swelling and the dyeing step to the dyeing step may be 1.2 to 4.0 times. If the cumulative stretch ratio is less than 1.2 times, wrinkles may occur in the film, and there is a possibility of poor appearance. If it exceeds 4.0 times, the initial optical properties may become weak.

<Crosslinking step>

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

When the iodine of the dichroic dye is insufficient in the cross-linking reaction, the iodine molecules will be detached through the moist heat environment, so a sufficient cross-linking reaction is required. In addition, in order to align the iodine molecules located between the molecules of the polarizer-forming thin film and improve the optical properties, it is possible to perform stretching at the maximum stretching ratio in the crosslinking step.

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

The above-mentioned aqueous solution for cross-linking can use the well-known cross-linking aqueous solution in this field without particular limitation. For example, it can contain water and boric acid or boron compounds such as sodium borate, which belong to the solvent, or it can be mixed with water. of organic solvents and iodides.

The boron compound imparts short cross-linking bonds and rigidity to the polarizer, suppresses the occurrence of wrinkles on the film during the process, improves the handleability of the film, and has the effect of forming the iodine alignment of the polarizer.

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

In this step, the iodide can be used to maintain the uniformity of the polarization degree in the plane of the polarizer and prevent the dyed iodine from falling off. The aforementioned iodide may be the same as that used in the aforementioned dyeing step, and its content may be 0.05 to 15% by weight relative to 100% by weight of water, but not limited thereto, preferably 0.5 to 11% by weight. When its content is less than 0.05% by weight, the iodide ions in the film will be detached and there is a possibility of increasing the transmittance of the polarizer. When it exceeds 15% by weight, the iodine ions in the aqueous solution may penetrate into the film and may reduce the transmission of the polarizer. Rate.

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

The stretching step may be performed together with the aforementioned cross-linking step, and in this case, the stretching ratio of the aforementioned first cross-linking step may be 1.4 to 3.0 times, preferably 1.5 to 2.5 times.

Moreover, the extension ratio of the said 2nd crosslinking process may be 1.01 to 2.0 times, and may be preferably 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 alignment effect of iodine may become insufficient, and if it exceeds 5.0 times, the film may be broken through excessive stretching, and the production efficiency may be reduced.

<Complementary color step>

The manufacturing method of the polarizer of the present invention may also include a complementary color step as necessary. Through the color-compensating step, the iodine complex located between molecules in the film for forming a polarizer physically adsorbing the iodine complex can be aligned near the cross-linking of the boric acid to stabilize the iodine complex. Moreover, by the color-complementing step, the film for forming a polarizer in which the dyeing of the iodine complex in the above-mentioned cross-linking step is insufficient can be complemented.

The color-compensating aqueous solution in the aforementioned color-compensating step contains, for example, water as a solvent and boron compounds such as boric acid, and may also contain an organic solvent and iodide that are co-soluble with water.

In the present invention, the boron compound is used for short cross-linking bonds and rigidity to the polarizer, and by preventing the film from wrinkling in the process, it can Improve the handleability of the film and play the role of iodine alignment in the formation of polarizers.

Although content of the said boron compound may be 1 to 10 weight% with respect to 100 weight% of water, it is not limited to this, Preferably it may be 2 to 6 weight%. When the content is less than 1% by weight, the crosslinking effect of the boron compound is reduced, and it is sometimes difficult to impart rigidity to the polarizer. When it exceeds 10% by weight, the crosslinking reaction of the inorganic crosslinking agent is excessively activated. In some cases, the crosslinking reaction of the organic crosslinking agent is difficult to proceed efficiently.

In this step, the iodide can be used to maintain the uniformity of the in-plane polarization of the polarizer, and can also be used to prevent the dyed iodine from falling off. The aforementioned iodide can be the same as the one used in the aforementioned dyeing step, and its content can be 0.05 to 15 wt % relative to 100 wt % of water, but is not limited thereto, preferably 0.5 to 11 wt % %. When its content is less than 0.05% by weight, the iodide ions in the film may be detached and the transmittance of the polarizer may be increased. If it exceeds 15% by weight, the iodide ions in the aqueous solution will penetrate into the film, which may reduce the polarizer. transmittance.

In the present invention, the temperature of the color correction tank may be 20 to 70°C. The immersion time of the polarizer-forming film in the color-compensating 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 aforementioned color-compensating step. In this case, the stretching ratio of the color-compensating step can be 1.01 to 1.1 times, but not limited thereto, and preferably 1.02 to 1.08 times.

When the aforementioned elongation ratio is less than 1.01 times, the stabilization effect of the iodine complex may become insufficient. If the film is stretched, the film may be broken, and the production efficiency may be lowered.

<Extended step>

In the present invention, the extending 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 a plurality of times. In the case of carrying out a plurality of times, it may be carried out separately in any of the polarizer manufacturing steps.

In the manufacturing 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.

In this specification, "cumulative extension ratio" means the value of the product of extension ratios in each step.

<Water washing step>

The method for producing a polarizer of the present invention may further include a water washing step according to necessity, which is to immerse the polarizer-forming film that has been cross-linked and extended in a water washing tank filled with an aqueous solution for washing, and then the water washing step is performed. Unwanted residues such as boric acid adhering to the polarizer-forming film in the previous steps are removed.

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

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

The aforementioned water washing step may be omitted, or the step before the water washing step, such as the aforementioned dyeing step or the aforementioned cross-linking step, may be completed each time. Do it in an instant. 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 polarizer-forming film that has been washed with water, and is necked in by drying, which can further improve the orientation of the dyed iodine molecules and obtain excellent optical properties. steps of the polarizer. In addition, neck-in 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 polarizer by contacting the film for forming a polarizer with a heating roller, and the time for contacting the film for forming a polarizer with the heating roller is 50% or more of the total drying time.

As discussed above, the present invention can achieve the effect related to the present invention by contacting the film for forming a polarizer with the hot roller for drying, and at this time, the contact time between the film and the hot roller is adjusted to the full drying time more than 50%. The time for the polarizer-forming film to be in contact with the heated roller can be specifically 30 to 600 seconds, preferably 40 to 120 seconds, more preferably 40 to 60 seconds, and preferably 42 to 58 seconds Excellent.

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

In the present invention, the total drying time refers to the time during which the drying step is performed, and refers to the time during which any drying method is performed for the film for forming a polarizer. For example, when drying is performed by contacting a hot roll, the time that the film is in contact with the hot roll; when multiple hot rolls are used, the film is placed on the hot roll The time for conveying with the heat roller; the time for hot air to contact the film when hot air drying; the time for air to contact the film when air drying; the time for heating the film when heating and drying; the time for far infrared radiation when drying The time for the film; when microwave drying, the time for irradiating microwaves on the film, etc., are included in the total drying time. Therefore, the total drying time also includes the time of drying the film for forming a polarizer other than the method of drying in contact with a heat roll.

In the present invention, when the time in which the film for forming a polarizer is in contact with the heat roller is 50% or more of the total drying time, it is easy to manufacture a polarizer with 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 striped pattern that extends along the extension direction along 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 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).

In the present invention, in order to adjust the drying shrinkage value of the polarizer within the above-mentioned range, it can be adjusted by controlling the ratio of the heating roller drying time in the total drying time to 50% or more.

When the drying shrinkage value is in the above-mentioned range, the effect of reducing the shrinkage force in the absorption axis direction and the streak in the extension direction can be more pronounced. on.

In the present invention, in the drying step, hot air drying may be performed in parallel while the film for forming a polarizer is in contact with a hot 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 higher than the temperature of the hot air, for example, 5 to 20° C. high. The temperature of the heat roller is preferably 100° C. or lower from the viewpoint of preventing deterioration of the polarizer.

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

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

The polarizer of the present invention can provide a polarizer in which a polarizer protective film is bonded to at least one side of the polarizer.

The material of the polarizer protective film is not particularly limited, for example, various transparent resins containing 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 film.

Specific examples of the protective film include acrylate-based resin films such as polymethyl(meth)acrylate and polyethyl(meth)acrylate; polyethylene terephthalate, polyethylene isophthalate, etc. Polyester resin films such as polyester, polyethylene naphthate, and polybutylene terephthalate; cellulose resin films such as cellulose diacetate, cellulose triacetate, and cellulose acetate propionate; polyethylene , polypropylene, with ring system or norborn Polyolefin-based resin films such as polyolefin-based and ethylene-propylene copolymers having an olefinic structure, etc., are not limited to these.

Although the thickness of the said protective film is not specifically limited, It can be 10-200 micrometers, Preferably it is 10-150 micrometers. When the polarizer protective films are laminated on both sides of the polarizer, the protective films may have the same or different thicknesses from each other.

The bonding of the polarizer and the polarizer protective film can be performed using an adhesive composition. The bonding of the polarizer and the protective film using the adhesive composition can be performed 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. , spray method, etc., a method in which the adhesive composition is applied on the adhesive surface of the polarizing film and/or the protective film, and then the two are superimposed. The casting method refers to a method in which the polarizer or protective film of the object to be coated is moved approximately in the vertical direction, approximately in the horizontal direction, or in an oblique direction between the two, and at the same time, an adhesive composition is applied to the surface thereof.

After the adhesive composition is applied, the polarizer and the protective film are pinched 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. The saponification treatment includes a method of immersion in an alkaline aqueous solution such as sodium hydroxide and potassium hydroxide.

After laminating the polarizer and the polarizer protective film, drying treatment is performed. Drying treatment, for example, can be carried out by spraying hot air, but The temperature at this time can be appropriately selected in the range of 50 to 100 degrees. Drying time is usually 30 to 1,000 seconds.

The polarizing plate of the present invention can be suitably used not only in ordinary liquid crystal display devices, but also in various image display devices such as organic light-emitting display devices (OLED), plasma display devices, and electric field emission display devices.

Below, in order to facilitate the understanding of the present invention, the preferred embodiments are proposed, but these embodiments are only to illustrate the inventors of the present invention, and not to limit the scope of the appended patent application, and those skilled in the art can clearly understand the scope and technology of the present invention. Various changes and corrections can be made to the embodiments within the scope of the idea, and these changes and corrections naturally belong to the scope of the appended patent application.

<Example 1>

A transparent unstretched polyvinyl alcohol film (PE 60, manufactured by KURARAY) with a saponification degree of 99.9% or more was immersed in water (deionized water) at 25°C for 2 minutes to swell (swelling step), and then swelled with iodine-containing water. Dyeing was performed by immersing in 2.0 mM/L in 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, extension was performed at an extension ratio of 1.482 times and 1.607 times, respectively. Next, 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 for 39 seconds (cross-linking step) to perform a cross-linking reaction, and at the same time, stretched at a stretching ratio of 2.266 times. . Next, it was immersed in an aqueous solution for color correction 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. seconds (complementary color step), while extending 1.05 times.

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

Triacetate cellulose (TAC) films were laminated on both sides of the manufactured polarizer to form a 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 respective temperatures and drying time of the heat roller and the hot air were adjusted.

<Test example>

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

<1. Measurement of drying shrinkage>

Drying neck-in, which means the reduction ratio before and after drying of the polarizer, is measured by the aforementioned mathematical formula 1.

<2. Measurement of the degree of streaks>

After manufacturing the polarizing plate, observe whether there is accompanying by the fluorescent lamp reflection method The streak-like unevenness extending in the extending direction of the unevenness was visually confirmed using the following criteria. The fluorescent lamp reflection method refers to a method in which light from a fluorescent lamp is incident from an oblique direction of about 45°, and the unevenness of a polarizing plate is visually checked and evaluated in the reflected light.

Lv1.: The level of streaks cannot be confirmed in the obtained polarizer

Lv2.: In the obtained polarizing plate, although the speckle can be visually recognized by the fluorescent lamp reflection method, it is not visually recognized at a level

Lv3.: In the obtained polarizing plate, the speckle can be visually recognized by the fluorescent lamp reflection method, and the level can be recognized by visual inspection

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

After cutting the produced polarizer into a size of 1 cm×1 cm, the arithmetic mean height in the polarizer plane was measured according to 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 polarizer was measured. The polarizers produced in Examples and Comparative Examples were cut into a size of 3.0 cm (absorption axis direction) × 2 mm (transmission axis direction), and were measured at 80° C. statically by DMA Q800 (Dynamic mechanical analyzer, TA company). The contraction force in the axial direction was absorbed when left for 4 hours. At this time, in order to maintain a flat state of the polarizer before the measurement, a minimum load was applied in the thickness direction of the polarizer, and the measurement was performed.

<5. Optical properties (degree of polarization)>

The produced polarizer was cut into a size of 4 cm×4 cm, and then the transmittance was measured using an ultraviolet visible ray spectrometer (V-7100, manufactured by JASCO Corporation). over rate. At this time, the degree of polarization is defined by the following formula 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 the absorption axes of _a pair of polarizers are arranged in a parallel state, and T2 is the vertical transmittance obtained when the absorption axes of a pair of polarizers are arranged in a vertical state).

Referring to Table 2, it can be confirmed that the polarizer having undergone the drying step of the present invention has a degree of polarization almost equal to that of Comparative Examples 3 and 5 which were only dried with hot air. There is no inferiority, and compared with the whole comparative example, the streak-like unevenness extending along the extending direction accompanying the unevenness and the shrinkage force in the absorption axis direction were also confirmed to be significantly reduced.

Claims (9)

A polarizer whose arithmetic mean height (Sa) is 14.4 nm or more and 21.0 nm or less. According to the polarizer described in item 1 of the claimed scope, the thickness of the polarizer is 5 to 30 μm. According to the polarizer described in claim 1 or 2, the shrinkage force in the direction of the absorption axis of the polarizer is 3N/2mm or less. A manufacturing method of a polarizer, the manufacturing method is to manufacture the polarizer described in any one of items 1 to 3 of the scope of application, the method comprising: swelling, dyeing, stretching, crosslinking, and The drying step, the aforementioned drying step, includes a step of drying the polarizer-forming film in contact with the heated roller, and the time during which the polarizer-forming film is in contact with the heated roller 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 manufacturing a polarizer according to claim 5, wherein the temperature of the heat roller is higher than the temperature of the hot air. The method for manufacturing a polarizer according to any one of the claims 4 to 6, wherein the drying shrinkage value defined by the following mathematical formula 1 is 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). A polarizing plate comprising the polarizing plate described in any one of claims 1 to 3 of the patent application scope and a polarizing plate protective film bonded to at least one side of the polarizing plate. An image display device, the image display device includes the polarizing plate as described in item 8 of the patent application scope.