KR20100102292A - Preparing method for polarizer, polarizer and polarizing plate comprising the same - Google Patents

Abstract

PURPOSE: A manufacturing method of a polarizer and a polarizing plate thereof are provided to prevent the twist of a liquid crystal cell by reducing a difference between the shrinkage in an absorption axis due to a thermal stress and the shrinkage in a transmission axis direction. CONSTITUTION: A polyvinyl alcoholometer film is dry-extended with a traverse extension ration of 2 or 2.5 times in a traverse direction. A wet-extended polyvinyl alcohol film is dry-extended with a longitudinal extension ration of 4.5 or 7 times in a longitudinal direction.

Description

Manufacturing method of polarizer, polarizer and polarizing plate equipped with it {PREPARING METHOD FOR POLARIZER, POLARIZER AND POLARIZING PLATE COMPRISING THE SAME}

The present invention relates to a manufacturing method of a polarizer with a shrinkage rate adjusted to prevent distortion of the liquid crystal cell to improve light leakage, a polarizer, and a polarizing plate provided with the same.

In order to provide images with high brightness and excellent color reproducibility to various image display devices such as liquid crystal display (LCD), electroluminescence (EL) display, plasma display (PDP), and field emission display (FED), Constant research has been conducted.

To date, most polarizers swell a polymer film such as a polyvinyl alcohol (PVA) film, dye the swollen polymer film to adsorb a substance such as dichroic iodine or dichroic dye, and then crosslink the reaction. It was prepared by fixing the adsorbed dye and orienting the fixed dye through stretching.

On the other hand, in recent years, as the liquid crystal display device is gradually enlarged, the polarizing plate used is also enlarged. Accordingly, the uniformity of luminance and the improvement of optical characteristics are required in the plane.

However, the polarizer constituting the polarizing plate has a large shrinkage force in the stretching axis direction, and when thermal stress is applied, the dimensional change due to thermal deformation occurs. In particular, the polarizer manufactured by the uniaxial stretching method as in the prior art has an absorption axis direction (length The shrinkage in the longitudinal, longitudinal, and MD directions is greater than the shrinkage in the transmission axis directions (width, transverse, and TD directions), and the liquid crystal cell is distorted due to the difference in thermal shrinkage. As a result, uniformity of luminance in the plane of the liquid crystal display is lowered and light leakage occurs. This phenomenon becomes more serious as the liquid crystal display becomes larger.

In order to improve the distortion of the liquid crystal cell according to the dimensional change as described above, a method of minimizing or reducing the residual stress applied to the polarizer and the polarizer has been proposed. Specifically, as a method of removing the stress by forming a protective layer on the polarizer or polarizing plate, Korean Laid-Open Patent Publication No. 2003-0025213 discloses shrinkage force and dimensional change rate by laminating a transparent protective layer on at least one surface of the polarizing film and heating. A method of reducing is disclosed. However, in such a method, the thickness of the polarizing plate is increased due to the formation of the protective layer, and thus the demand for weight reduction and thinning, which is required with the enlargement of the liquid crystal display device, is difficult to satisfy.

In addition, as a method of reducing the overall residual stress by adjusting the thickness of the polarizer or the polarizing plate thinly, Korean Laid-Open Patent Publication No. 2001-0113559 uses a PVA film having a thickness of 60 ㎛ or less, by adjusting the stretching or crosslinking method to a thickness of 10 A method of manufacturing a polarizer having a thickness of -18 μm, which has little dimensional change and solves problems such as color unevenness and discoloration, has been disclosed. However, by this method, the absolute amount of residual stress in the stretching axis direction is reduced to reduce the shrinkage rate, but it is impossible to reduce the residual stress in the transmission axis direction perpendicular to the stretching axis.

As described above, the conventional methods improve only the dimensional change rate (shrinkage rate) of the polarizer in the absorption axis direction, but when the polarizer is applied to the upper and lower polarizing plates of the liquid crystal display device, the mutual angle difference between these absorption axes is 90 °. Therefore, when only the dimensional change rate in the absorption axis direction is improved, shrinkage in the upper and lower polarizing plates is different due to thermal stress, and thus it is difficult to sufficiently improve the distortion of the liquid crystal cell, and thus light leakage phenomenon still occurs.

An object of the present invention is to provide a method of manufacturing a polarizer that can prevent distortion and improve light leakage when applied to a liquid crystal cell by controlling not only the shrinkage of the polarizer in the absorption axis but also the shrinkage of the polarization in the transmission axis. do.

In addition, another object of the present invention is to provide a polarizer manufactured by the above production method.

In addition, another object of the present invention is to provide a polarizing plate and a liquid crystal display device provided with the polarizer.

The present invention comprises a first drawing step of dry stretching the polyvinyl alcohol-based film at a transverse stretching ratio of 2.00 to 2.50 times in the transverse direction (width direction); And a second stretching step of wet stretching the polyvinyl alcohol-based film that has been stretched in the longitudinal direction (length direction) at a longitudinal stretch ratio of 4.50 to 7.00 times.

In addition, the present invention provides a polarizer manufactured by the above production method.

In addition, the present invention provides a polarizing plate in which a polarizer protective film is laminated on at least one surface of the polarizer.

In addition, the present invention provides a liquid crystal display device having the polarizing plate on at least one side of the liquid crystal cell.

According to the present invention, by stretching by the biaxial stretching method of dry transverse stretching and wet longitudinal stretching, the shrinkage in the absorption axis direction due to thermal stress, the shrinkage in the transmission axis direction due to thermal stress, and the difference between these shrinkage rates to reduce the difference between the liquid crystal cell It is possible to prevent distortion and improve light leakage, and at the same time to achieve a lighter weight and a thinner liquid crystal display.

The present invention relates to a manufacturing method of a polarizer, a polarizer and a polarizing plate provided with the shrinkage is adjusted to prevent distortion of the liquid crystal cell to improve the light leakage phenomenon.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

Method for producing a polarizer of the present invention comprises a first stretching step of dry stretching the polyvinyl alcohol-based film at a transverse stretching ratio of 2.00 to 2.50 times in the transverse direction (width direction); And a second stretching step of wet stretching the polyvinyl alcohol-based film that has been stretched in the longitudinal direction (length direction) at a longitudinal stretching ratio of 4.50 to 7.00 times.

The polymer film for producing the polarizer is not particularly limited in kind, for example, PVA film, partially gummed PVA film; Hydrophilic polymer films such as polyethylene terephthalate films, ethylene-vinyl acetate copolymer films, cellulose films, partially gumified films thereof, and polyene oriented films such as dehydrated PVA films, dehydrochlorinated polyvinyl chloride, and the like. Can be mentioned. Among these, the PVA film is more preferable in that it is not only excellent in the effect of strengthening the uniformity of the degree of polarization in plane, but also excellent in dyeing affinity for a dichroic substance, for example, iodine, as a polarizer.

The method for producing the PVA film is not particularly limited, and examples thereof include a flow cast method, a cast method, an extrusion method, and the like, which form a film by flow casting a polymer stock solution decomposed into water or an organic solvent. In this case, in order to obtain the polarizer which is excellent in the uniformity of the polarization degree in the surface of a film, it is preferable that the in-plane retardation deviation of a PVA system film is small. Therefore, the retardation deviation in the PVA-based film as the raw material film before processing is preferably 1 to 100 nm, more preferably 10 nm or less, most preferably 5 nm or less, as measured at a measurement wavelength of 1000 nm.

The degree of polymerization of the PVA film is usually 500 to 10,000, preferably 1,000 to 6,000, and more preferably 1,400 to 4,000. In the case of the PVA-based saponification film, the saponification degree is preferably 95.0 mol% or more, more preferably 99.0 mol% or more, and most preferably 99.9 mol% or more from the viewpoint of solubility.

Usually, the method of manufacturing a polarizer includes a swelling step, a dyeing step, a crosslinking step, an stretching step, and a washing and drying step, and are mainly classified according to the stretching method. For example, a dry stretching method of stretching and dyeing a polymer film as a raw material by stretching in a hot roll, a wet stretching method of simultaneously stretching and crosslinking while impregnated with hot water, or a combination of the two stretching methods Hybrid drawing method is mentioned. Among these, the manufacturing method of the polarizer of this invention is the hybrid extending | stretching method which mixed the dry extending | stretching method and the wet extending | stretching method, and especially the extending | stretching method using biaxial stretching of dry transverse stretching and wet longitudinal stretching.

A method of manufacturing a polarizer according to an embodiment of the present invention includes a first stretching step (dry lateral stretching) performed before the swelling step and a second stretching step (wet longitudinal stretching) performed after the first stretching step. .

The first stretching step is a step of dry stretching the PVA-based film in the lateral direction (width direction), and is a step of effectively controlling the stretching ratio without imparting polarization characteristics.

The draw ratio of the first draw step, ie the lateral draw ratio, is preferably 2.00 to 2.50 times, more preferably 2.00 to 2.20 times. When the lateral stretch ratio is less than 2.00 times or exceeds 2.50 times, the difference between the shrinkage rate in the absorption axis direction and the shrinkage rate in the transmission axis direction of the PVA-based film cannot be reduced as desired.

The first stretching step is preferably performed before the swelling step, and may be performed by passing the PVA film at a constant speed between heating rolls or by pulling the PVA film in the width direction by using a tenter or the like.

It is preferable that the temperature of a 1st extending | stretching step is 80-200 degreeC, More preferably, it is 85-150 degreeC.

The second stretching step is a step of primary stretching, that is, wet stretching the dry transversely stretched PVA film in the longitudinal direction (length direction), and may be performed together in one or more of the swelling step, the dyeing step and the crosslinking step. Or may be carried out in an independent stretching step.

The draw ratio of the second draw step, that is, the longitudinal draw ratio is preferably 4.50 to 7.00 times, more preferably 4.80 to 6.20 times. If the longitudinal stretch ratio is less than 4.50 times, there is a problem that the polarization degree is lowered, and if it exceeds 7.00 times, there is a problem that the film is easily broken.

In the present specification, "extension ratio" means the ratio of stretching at each stage, "cumulative stretching ratio" means the value of the product of the stretching ratio of each stage. For example, when the second stretching step is performed together in the swelling, dyeing, and crosslinking steps, the value obtained by multiplying the respective longitudinal drawing ratios in the swelling, dyeing, and crosslinking steps becomes the cumulative longitudinal draw ratio, and the cumulative longitudinal draw ratio is the second. It is the total longitudinal draw ratio of the stretching stage.

The swelling step, the dyeing step and the crosslinking step and the washing step carried out after the crosslinking step are performed in a state in which the PVA-based film is immersed in a bath filled with at least one solution selected from several kinds of solutions.

In addition, the order of the steps and the number of repetitions are not particularly limited, and the steps may be performed simultaneously or sequentially, and some steps may be omitted.

The swelling step is a step of immersing the unstretched PVA film in a swelling tank filled with an aqueous solution for swelling. Through this step, impurities such as dust or blocking agents deposited on the surface of the PVA-based film may be cleaned, and the PVA-based film may be swollen to improve the stretching efficiency and to prevent dyeing unevenness.

Deionized water may be used alone as the aqueous solution for swelling, and when a small amount of glycerin and potassium iodide is added thereto, the processability may be improved along with the swelling of the PVA-based film. It is preferable that content of glycerin is 5 weight% or less with respect to 100 weight% of aqueous solutions for swelling, and content of potassium iodide is 10 weight% or less.

It is preferable that the temperature of a swelling tank is 20-45 degreeC, More preferably, it is 25-40 degreeC.

The execution time (swelling tank immersion time) of the swelling step is preferably 2 to 180 seconds, more preferably 10 to 150 seconds, most preferably 60 to 120 seconds.

A part of the second drawing step may be performed together with the swelling step, wherein the longitudinal drawing ratio is preferably 1.10 to 3.50 times.

The dyeing step is a step of adsorbing iodine on the PVA-based film by immersing the swollen PVA-based film in a dye bath filled with a dichroic material, for example, an aqueous solution for dyeing including iodine.

The aqueous solution for dyeing may include deionized water or a water-soluble organic solvent and iodine. The content of iodine is preferably 0.010 to 10% by weight, more preferably 0.020 to 7% by weight, most preferably 0.025 to 5% by weight based on 100% by weight of the aqueous solution for dyeing. Iodide may be further included together with iodine to further improve dyeing efficiency. As iodide, potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, titanium iodide, etc. may be used alone or in combination of two or more thereof. Of these, potassium iodide is preferred. The content of iodide is preferably 0.010 to 10% by weight, more preferably 0.100 to 5% by weight relative to 100% by weight of the aqueous solution for dyeing. The weight ratio of iodine to iodide (potassium iodide) is preferably 1: 5 to 1: 100, more preferably 1: 6 to 1:80, and most preferably 1: 7 to 1:70.

Moreover, it is preferable that the aqueous solution for dyeing further contains a small amount of crosslinking agents. As the crosslinking agent, one or more selected from boron compounds such as boric acid and sodium borate, glyoxal and glutaraldehyde can be used, and preferably, a combination of boron compounds such as boric acid and sodium borate is used. When such a component is further included, there is an effect of further strengthening the crosslinking of the iodine molecule. The content of the crosslinking agent is preferably 0.01 to 6% by weight, more preferably 0.10 to 3% by weight based on 100% by weight of the aqueous solution for dyeing.

It is preferable that the temperature of a dye bath is 5-42 degreeC, More preferably, it is 10-35 degreeC. Moreover, the immersion time of a PVA system film in a dyeing tank is not specifically limited, Preferably it is 1 to 20 minutes, More preferably, it is 2 to 10 minutes.

A part of the second drawing step may be performed together with the dyeing step, and in this case, the cumulative longitudinal drawing ratio is preferably 1.10 to 4.00 times.

In addition to the above-described dyeing method, a method of applying or spraying a dye solution containing iodine on the PVA-based film may be used, or iodine may be dyed by mixing with PVA resin before casting the PVA-based film.

The crosslinking step is a step of fixing the adsorbed iodine molecules by immersing the dyed PVA film in an aqueous solution for crosslinking.

The aqueous solution for crosslinking may include at least one crosslinking agent selected from deionized water as a solvent, a boron compound such as boric acid, sodium borate, glyoxal and glutaldehyde. In addition, the organic solvent may be further dissolved together with the deionized water. The content of the crosslinking agent is not particularly limited and is preferably 1 to 10% by weight, more preferably 2 to 6% by weight based on 100% by weight of the aqueous solution for crosslinking.

In addition, the aqueous solution for crosslinking may further include a small amount of iodide in order to obtain uniformity of the degree of polarization in the polarizer plane. Iodide may be the same as the one used in the dyeing step, the content may be 0.05 to 15% by weight, preferably 0.50 to 11% by weight relative to the total content of the aqueous solution for crosslinking (100% by weight). . Most preferably, boric acid and potassium iodide are used in combination, and in this case, the weight ratio of boric acid and potassium iodide is preferably 1: 0.1 to 1: 3.5, more preferably 1: 0.5 to 1: 3.0.

The temperature of the crosslinking bath is 20 to 70 ° C., and the immersion time of the PVA film in the crosslinking bath may be 1 second to 15 minutes, preferably 5 seconds to 10 minutes.

A part of the second stretching step may be performed together with the crosslinking step, in which case the longitudinal draw ratio is preferably 1.10 to 4.00 times, and the cumulative longitudinal draw ratio is preferably 4.50 to 7.00 times.

In addition to the crosslinking method as described above, a method of applying or spraying a crosslinking solution containing a crosslinking agent on a PVA-based film may be used.

As such, when the second stretching step is performed together with one or more of the swelling step, the dyeing step and the crosslinking step, the total cumulative longitudinal draw ratio may be stretched to be 4.50 to 7.00 times.

In addition, the second stretching step may be performed as an independent stretching step using a separate drawing tank filled with an aqueous solution for drawing.

The type of the aqueous solution for stretching is not particularly limited, and may be a solution containing at least one selected from a solvent such as water, ethanol or an organic solvent and a metal salt, iodine, boron, and a zinc compound. In particular, a solution containing 2 to 18% by weight boric acid, 2 to 10% by weight potassium iodide or mixtures thereof is preferred. In addition, when boric acid and calcium iodide are used together, their weight ratio is preferably 1: 0.1 to 1: 4, more preferably 1: 0.5 to 1: 3.

It is preferable that the temperature of a drawing tank is 40-67 degreeC, More preferably, it is 50-62 degreeC.

The stretching method is not particularly limited, and for example, in the case of roll stretching, a stretching method is used based on the difference in circulation speed between rolls.

In the present specification, the value of the product of the lateral draw ratio in the first draw step and the longitudinal draw ratio in the second draw step is referred to as "stretch ratio," and the draw ratio is preferably 9.00 to 15.50 times, preferably 9.50 to 11.50 times. desirable. In this range, not only the shrinkage in the absorption axis (length direction) direction of the PVA film but also the shrinkage in the transmission axis (width direction) direction can be reduced together, and the difference thereof can be minimized.

According to the biaxial stretching method of the dry transverse stretching as the first stretching stage and the wet longitudinal stretching as the second stretching stage, not only the shrinkage rate in the absorption axis (length direction) direction of the PVA film but also the shrinkage rate in the transmission axis (width direction) direction are included. Can be reduced, and the difference between them can be minimized.

The washing step is to remove unnecessary residues such as boric acid deposited on the PVA film in the previous steps by immersing the PVA-based film completed crosslinking and stretching in a cleaning tank filled with an aqueous solution for cleaning.

The aqueous cleaning solution may be deionized water, and an iodine compound may be further added thereto. As the iodide, the same ones as used in the dyeing step can be used, and among them, it is preferable to use sodium iodide or potassium iodide. The content of potassium iodide may be 0.1 to 10% by weight with respect to 100% by weight of the aqueous solution for cleaning, preferably 3 to 8% by weight.

It is preferable that the temperature of a washing tank is 10-60 degreeC, More preferably, it is 15-40 degreeC.

The washing step may be repeated one or more times, and the number of repetitions is not particularly limited. In addition, the type and content of the components of the aqueous solution for cleaning may be changed according to the number of times repeated.

The washing step may be performed whenever previous steps such as swelling step, dyeing step, crosslinking step or stretching step are completed.

In the steps as described above, when the PVA-based film is raised in the air from the reaction tank, in order to prevent the liquid, such as a solution attached to the PVA-based film from falling, conventionally known liquid cutting rolls such as pinch rolls ( A liquid-cutting roll may be used, or excess solution may be removed by a liquid cutting method using an air knife.

The drying step is a step of obtaining a polarizer in which iodine is adsorbed and oriented by drying the washed PVA film.

As a drying method, a method such as natural drying, air drying, heating drying, etc. may be used, and heat drying is preferably used. For example, it may be heat dried at 20 to 80 ℃ for 1 to 10 minutes. The drying temperature is preferably low in order to prevent deterioration of the polarizer, more preferably 60 ° C. or less, most preferably 45 ° C. or less.

In addition to the above method, any other method including a first drawing step and a second drawing step may produce a polymer film polarizer in which a dichroic material is adsorbed and oriented. For example, a method of kneading a dichroic material and a resin and then stretching, a method of using a dichroic dye as a guest and a liquid crystal oriented in a single axis as a host (US Patent No. 5,523,863, Japanese Patent Application Publication No. 1991-503321) Or a method using a dichroic solution liquid crystal (US Pat. No. 6,049,428), or the like.

In the method of manufacturing a polarizer of the present invention comprising such a step, the shrinkage rate (A) in the absorption axis direction and the shrinkage rate (B) in the absorption axis direction when measured after heating the polarizer to 5 ° C./min from room temperature to 100 ° C. It is preferable to make these respectively 1.50% or less. At the same time, the difference (| A-B |) between the shrinkage rate A in the absorption axis direction and the shrinkage rate B in the transmission axis direction is preferably 0.2 or less, more preferably 0.1 or less.

The polarizer of the present invention is characterized in that it is produced by the manufacturing method of the polarizer.

The thickness of the polarizer is not particularly limited and is preferably 5 to 40 µm. In the case of such a thickness, deterioration of mechanical strength and optical properties can be prevented, and when applied to a polarizing plate or an image display device, light leakage phenomenon can be improved, and weight and thickness can be achieved while maintaining optical properties.

It is preferable that the shrinkage rate (A) in the absorption axis direction and the shrinkage rate (B) in the transmission axis direction, respectively, measured after heating the polarizer at room temperature to 100 ° C. at 5 ° C./min, more preferably 0.10%. To 1.00%. At the same time, it is preferable that the difference (| A-B |) between shrinkage rates is 0.2 or less, More preferably, it is 0.1 or less.

In this case, when the difference between the shrinkage rate and the shrinkage rate is controlled, not only the shrinkage rate in the absorption axis direction of the polarizer but also the shrinkage rate in the transmission axis direction are reduced together and the difference thereof is minimized. This heat stress prevents distortion and improves light leakage.

The transmittance of the polarizer is preferably 40.0% or more, and more preferably 41.0 to 45.0%.

It is preferable that the orthogonal transmittance measured at the conditions which superimposed two sheets mutually so that the absorption axis of a polarizer may cross | intersect with each other by 90 degree is low, More preferably, it is 0.030% or less, Most preferably, it is 0.020% or less.

In addition, the degree of polarization is preferably 99.0 to 100%.

Polarizing plate of the present invention is characterized in that the polarizer protective film is laminated on at least one surface of the polarizer.

In the polarizing plate according to the exemplary embodiment of the present invention, as shown in FIG. 3, the polarizer protective film 2 and the surface protective film 1 are laminated in order on one surface of the polarizer 3, and the other one. The surface may have a structure in which the polarizer protective film 2, the pressure-sensitive adhesive layer 4, and the release film 5 are sequentially stacked.

The structure of the polarizing plate is not particularly limited, and various kinds of optical layers capable of satisfying required optical properties may be laminated on the polarizer. For example, a structure in which a polarizer protective film for protecting the polarizer is laminated on at least one surface of the polarizer; A structure in which a surface treatment layer such as a hard coating layer, an antireflection layer, an anti-sticking layer, a diffusion barrier layer, an antiglare layer, or the like is laminated on at least one surface of the polarizer or the polarizer protective film; It may have a structure in which an alignment liquid crystal layer or another functional film is laminated on at least one surface of the polarizer or the polarizer protective film. In addition, a phase difference including a wavelength plate (including a λ plate) such as an optical film, a reflector, a semi-transmissive plate, a 1/2 wave plate, or a quarter wave plate, such as a polarization conversion device used to form various image display devices At least one of the plate, the viewing angle compensation film, and the brightness enhancement film may be laminated with an optical layer. More specifically, a polarizer having a structure in which a polarizer protective film is laminated on one surface of a polarizer, the polarizing plate comprising a reflective polarizer or a semi-transparent polarizer in which a reflector or a transflective reflector is laminated on the laminated polarizer protective film; An oval or circular polarizing plate in which retardation plates are stacked; A wide viewing angle polarizer on which a viewing angle compensation layer or a viewing angle compensation layer is stacked; Or the polarizing plate in which the brightness improving film was laminated | stacked is preferable.

The surface protection film 1 is for protecting a polarizing plate, and can use a conventional surface protection film in which an adhesive layer is formed on a base film.

As the polarizer protective film 2, an excellent film in transparency, mechanical strength, thermal stability, moisture shielding, isotropy, etc. may be used. Specific examples thereof include polyethylene terephthalate, polyethylene isophthalate, polyethylene naphthalate, and polybutylene terephthalate. Polyester films such as these; Cellulose films such as diacetyl cellulose and triacetyl cellulose; Polycarbonate film; Acrylic films such as polymethyl (meth) acrylate and polyethyl (meth) acrylate; Styrene films such as polystyrene and acrylonitrile-styrene copolymers; Polycarbonate film; Polyolefin-based films such as polyethylene, polypropylene, cyclo-based or norbornene-structured polyolefins, ethylene propylene copolymers; Vinyl chloride film; Amide films such as nylon and aromatic polyamides; Imide film; Polyether sulfone-based film; Sulfone film; Polyether ether ketone film; Sulfided polyphenylene-based films; Vinyl alcohol film; Vinylidene chloride-based film; Polyoxymethylene film; Epoxy type film etc. are mentioned. In addition, the polarizer protective film may be a cured layer formed from a thermosetting or ultraviolet curable resin such as aryl resin, urethane resin, acrylic-urethane resin, epoxy resin, silicone resin and the like. Among these, especially the cellulose type film which has the surface saponified by alkali etc. is preferable in consideration of polarization characteristic or durability. In addition, in consideration of polarization characteristics, durability and bonding characteristics, it is preferable that the surface of the polarizer protective film is saponified by alkali or the like.

The thickness of the polarizer protective film is not particularly limited, and may be usually 500 μm or less, preferably 1 to 300 μm, more preferably 5 to 200 μm.

It is preferable that a polarizer protective film is colorless, and Rth = [(nx + ny) / 2-nz] xd in a thickness direction (where nx and ny are principal refractive index in a plane, nz is refractive index in a thickness direction) d is the thickness of the film), where the retardation (phase retardation) value Rth is preferably -90 to +75 nm, more preferably -80 to +60 nm, most preferably -70 to +45 nm Is used. When such a protective film is used, the coloring (optical coloring) of the polarizing plate generated by the protective film can be almost eliminated.

The polarizer 3 is manufactured by the polarizer manufacturing method of this invention, and is a polarizer whose thickness is 5-40 micrometers.

The pressure-sensitive adhesive layer 4 may be formed of a common pressure-sensitive adhesive such as acrylic, silicone, polyester, polyurethane, polyether or rubber. The pressure-sensitive adhesive layer absorbs moisture in consideration of peeling phenomenon due to moisture absorption, bubble generation and distortion of the liquid crystal cell due to differences between coefficients of thermal expansion, and prevention of deterioration of optical characteristics, such as moldability of an image display device excellent in quality and durability. It is preferable that the rate is low and excellent in heat resistance. It is also desirable to not require any high temperature treatment, such as curing or drying, or to require long term curing or drying in view of the optical properties. From this point of view, acrylic pressure-sensitive adhesives are preferably used.

The release film 5 is a film for protecting the pressure-sensitive adhesive layer, the type is not particularly limited as long as it is a film commonly used in the art. Specific examples include polyethylene, polypropylene, poly-1-butene, poly-4-methyl-1-pentene, ethylene-propylene copolymer, ethylene-1-butene copolymer, ethylene-vinyl acetate copolymer, ethylene-ethylacrylic Polyolefin type films, such as a rate copolymer and an ethylene-vinyl alcohol copolymer; Polyester-based films such as polyethylene terephthalate, polyethylene naphthalate and polybutylene terephthalate; Polyamide films such as polyacrylate, polystyrene, nylon 6 and partially aromatic polyamide; Polyvinyl chloride film; Polyvinylidene chloride film; Or polycarbonate films. These may be those which have been appropriately released by a release agent such as silicon-based, fluorine-based or silica powder.

The liquid crystal display of the present invention is characterized in that the polarizing plate is provided on at least one side of the liquid crystal cell.

In the present invention, since the liquid crystal display device is well known to those skilled in the art of the present invention, a detailed description of each configuration is omitted.

In addition to the liquid crystal display device, the present invention can be applied to various image display devices such as electroluminescent display devices, plasma display devices, and field emission display devices.

Hereinafter, preferred examples are provided to aid the understanding of the present invention, but the following examples are merely for exemplifying the present invention, and it will be apparent to those skilled in the art that various changes and modifications can be made within the scope and spirit of the present invention. It is natural that such variations and modifications fall within the scope of the appended claims.

Example 1

A PVA film (VF-PS, KURARAY Co., Ltd.) having a thickness of 75 µm was 2.00 times dry stretched in the transverse direction on a 120 ° C. heating roll. The dry transversely stretched PVA film was swelled by immersion in a swelling tank filled with deionized water at 30 ° C. for 3 minutes and immersed in a 30 ° C. aqueous solution for dyeing at 0.4 ° C. containing 0.4% by weight of iodine and 1.2% by weight of potassium iodide. The dye was crosslinked by immersion for 3 minutes in an aqueous solution for crosslinking at 60 ° C. containing 11.0% by weight of potassium iodide and 3.5% by weight of boric acid. At this time, the longitudinal stretching ratio was 1.40 times, 1.50 times, and 2.40 times in the swelling, dyeing, and crosslinking steps using a self-made drawing machine, and the PVA film was wet-stretched 5.04 times in the longitudinal direction. When the above step was completed, the PVA film was dried in an oven at 60 ℃ for 4 minutes to prepare a polarizer.

Example 2

The same process as in Example 1, but after the 2.00 times dry stretching in the transverse direction, the longitudinal stretching ratio in each swelling, dyeing and crosslinking step is 1.40 times, 1.60 times, 2.70 times, total wet stretching in the longitudinal direction 6.05 times It was.

Example 3

It carried out similarly to Example 1, but extended | stretched 2.50 times in the transverse direction.

Comparative Example 1

It carried out similarly to Example 1, but extended by 3.00 times in the transverse direction.

Comparative Example 2

The same process as in Example 1, but after 4.00 times dry stretching in the transverse direction, the longitudinal stretching ratio in each swelling, dyeing and crosslinking step is 1.20 times, 1.30 times, 1.90 times in total wet direction 2.96 times in the longitudinal direction It was.

Comparative Example 3

The same process as in Example 1, but after 2.00 times dry stretching in the transverse direction, the longitudinal stretching ratio of each of the swelling, dyeing and crosslinking step is 1.30 times, 1.40 times, 2.20 times the total wet type 4.00 times Stretched.

Comparative Example 4

The same process as in Example 1, except that the dry stretching in the transverse direction 1.80 times, the longitudinal stretching ratio in each of the swelling, dyeing and crosslinking step is 1.40 times, 1.50 times, 2.40 times wet stretching in the longitudinal direction total 5.04 times It was.

Comparative Example 5

It carried out similarly to Example 1, but did not carry out the crosswise dry drawing.

Test Example

Physical properties of the polarizers prepared in Examples and Comparative Examples were measured by the following methods, and the results are shown in Table 1 below.

(1) the thickness of the polarizer (㎛)

The thickness of the produced polarizer was measured using a digital gauge (DZ-501, Sony).

(2) shrinkage (%), shrinkage difference

The prepared polarizer was cut to have a width of 4 mm and a length of 8 mm with respect to the absorption axis and the transmission axis, respectively, to prepare a specimen. After the specimen was heated at a rate of 5 ° C./min from room temperature to 100 ° C., the change in length in the absorption axis and transmission axis directions was measured, and the shrinkage ratio was calculated based on Equation 1 below.

Shrinkage (%) = [(L ₀ -L ₁ ) / L ₀ ] × 100

(Wherein L ₀ is the length of the specimen before the heat treatment and L ₁ is the length of the specimen after the heat treatment.)

(3) transmittance (%), polarization degree (%)

The transmittance and polarization degree of the produced polarizer were measured using an ultraviolet visible light spectrometer (V-7100, manufactured by JASCO).

(4) Light leakage phenomenon

After bonding the transparent protective film to both sides of the polarizer prepared to prepare a polarizing plate, it was laminated to Corning's # 1737 glass to prepare a specimen. The specimen was heated at a rate of 5 ° C./min from room temperature to 100 ° C., and then visually confirmed whether there was a portion of light leaking from the specimen in the dark room, and evaluated based on the following criteria. At this time, the polarizing plate specimens were observed after being attached to both sides of the glass by 90 °.

○: Difficult to judge light leakage phenomenon

△: Some light leakage phenomenon

×: light leakage is vivid

division Stretch
Way Elongation ratio Shrinkage thickness
(Μm) Transmittance
(%) Polarization degree
(%) Light fountain
phenomenon Lateral Bell Absorption shaft
(%, A) Transmission axis
(%, B) | A-B | Example 1 2-axis 2.00 5.04 0.98 0.89 0.09 14.5 42.1 99.1 ○ Example 2 2-axis 2.00 6.05 1.25 1.08 0.17 12.3 42.4 99.3 △ Example 3 2-axis 2.50 5.04 1.49 1.30 0.19 11.5 41.5 99.1 △ Comparative Example 1 2-axis 3.00 5.04 2.00 1.60 0.40 8.1 34.0 96.5 × Comparative Example 2 2-axis 4.00 2.96 1.80 2.30 0.50 12.0 36.5 91.5 × Comparative Example 3 2-axis 2.00 4.00 1.21 0.91 0.30 18.4 37.9 98.5 × Comparative Example 4 2-axis 1.80 5.04 1.34 1.11 0.23 15.1 42.3 99.2 × Comparative Example 5 1 axis - 5.04 1.90 1.00 0.90 15.5 42.5 99.5 ×

As shown in Table 1, the polarizers of Examples 1 to 3 manufactured by the biaxial stretching method in which the dry transverse stretching ratio and the wet longitudinal stretching ratio were adjusted according to the present invention were maintained in the absorption axis direction and the transmission axis direction while maintaining the polarization degree. Shrinkage is less than 1.50%, respectively, and at the same time, the difference was also reduced to 0.2 or less, and it was confirmed that light leakage due to thermal stress could be improved.

On the other hand, the polarizers of Comparative Examples 1 to 4 in which the dry transverse stretching ratio or the wet longitudinal stretching ratio do not fall within the scope of the present invention and the polarizers of Comparative Example 5 manufactured by the conventional uniaxial stretching method do not have a contraction rate controlled compared to the examples. The difference was so large that the light leakage could not be sufficiently improved.

As described above, the polarizer manufactured according to the manufacturing method of the polarizer of the present invention, such as a liquid crystal display device, an electroluminescent display device, a plasma display device or a field emission display device, which requires improvement of light leakage while maintaining polarization degree Applicable to an image display device.

1 is a schematic diagram showing a lateral direction and a longitudinal direction of a PVA-based film,

2 is a cross-sectional view showing a polarizing plate with a polarizer of the present invention.

Explanation of symbols on the main parts of the drawings

a: width direction (lateral stretching direction, transmission axis, TD direction)

b: longitudinal direction (longitudinal stretching direction, absorption axis, MD direction)

1: surface protective film 2: polarizer protective film

3: polarizer 4: adhesive layer

5: release film

Claims (9)

A first stretching step of dry stretching the polyvinyl alcohol-based film at a transverse stretching ratio of 2.00 to 2.50 times in the transverse direction (width direction); And A method of manufacturing a polarizer comprising a second stretching step of wet stretching the polyvinyl alcohol-based film stretched in the longitudinal direction (length direction) at a longitudinal draw ratio of 4.50 to 7.00 times. The method of claim 1, wherein the first stretching step is performed before the swelling step. The method of claim 1, wherein the second stretching step is performed in at least one of a swelling step, a dyeing step, and a crosslinking step. The method of claim 1, wherein the draw ratio is 9.50 to 11.50 times. The shrinkage rate (A) in the absorption axis direction and the shrinkage rate (B) in the transmission axis direction are respectively 1.50% when measured after heating the prepared polarizer at a rate of 100 ° C./min from room temperature. The manufacturing method of light polarizer whose difference (| A-B |) is 0.2 or less. The polarizer manufactured by the manufacturing method of any one of Claims 1-5. The shrinkage rate (A) in the absorption axis direction and the shrinkage rate (B) in the transmission axis direction, respectively, when measured after heating at a rate of 100 ° C./min from room temperature, respectively, are 1.50%, and the difference between them (| A Polarizer with B |) of 0.2 or less. Polarizing plate in which a polarizer protective film is laminated on at least one surface of the polarizer of claim 6. A liquid crystal display device comprising the polarizing plate of claim 8.

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