KR20100102291A - Preparing method for thin polarizer, thin polarizer and polarizing plate comprising the same - Google Patents

Abstract

PURPOSE: A manufacturing method of a thin polarizer and a polarizing plate thereof are provided to prevent a polarizer from being easily damaged and to maintain optical characteristics. CONSTITUTION: A polyvinal alcoholometer film is wet-extended with a traverse extension ratio which is 1.3 or 1.9 times towards a horizontal direction. The wet-extended polyvinyl alcohol film is dry-extended with a longitudinal extension ration which is 5 or 7.2 times towards a longitudinal direction.

Description

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

The present invention relates to a method of manufacturing a thin polarizer, a thin polarizer, and a polarizing plate provided with the same, which can achieve light weight and thinness when applied to various image display apparatuses.

Recently, various image display devices such as liquid crystal display (LCD), electroluminescence (EL) display, plasma display (PDP), field emission display (FED), etc. have been gradually enlarged, and the demand for improvement of function and brightness has been increased. In addition, there is an increasing demand for thinner and lighter image display devices. For this reason, the research on the thinning and weight reduction of the polarizer or polarizing plate used for an image display apparatus is progressing.

In order to solve the thinning and weight reduction of the polarizing plate, a method of reducing the thickness of a substrate, for example, a transparent protective film laminated on both sides of the polarizer, and a method of reducing the thickness of the polarizer itself have been proposed.

In general, most polarizers swell a polymer film such as a polyvinyl alcohol (PVA) film having a thickness of about 75 μm, dye, adsorb a substance such as dichroic iodine or dichroic dye, and then crosslink the reaction. It is prepared by a method of orienting the dye is fixed by fixing the dye adsorbed through, and stretched at a draw ratio of 3 to 7 times, and finally has a thickness of about 25 to 35㎛.

Conventionally, in order to reduce the thickness of the polarizer, the PVA film is uniaxially stretched in the longitudinal direction (longitudinal direction or MD (Machine Direction) direction) or in the width direction (lateral direction or TD (Transverse Direction) direction), A method of using a high or thin PVA film has been proposed. Specifically, when uniaxially stretching in the longitudinal direction 8 times or uniaxially stretching 4 times or more in the width direction using a tender method or the like, the thickness of the polarizer is 20 µm or less. In addition, when uniaxially stretching by 6 times or more using a PVA film with a thickness of 50 µm, a polarizer having a thickness of 20 µm or less can be obtained. However, when manufacturing a polarizer by this method, there exists a problem that a polarizer breaks easily during a process.

Korean Laid-Open Patent Publication No. 2004-0069948 and Japanese Laid-Open Patent Publication No. 2004-233871 disclose a method of manufacturing a polarizer having a thickness of about 5-22 μm by obliquely stretching a PVA film using a tender method or the like. However, the oblique stretching method is advantageous in the cutting step for applying to the polarizing plate for small and medium image display apparatuses because the absorption axis of the polarizer is inclined, but is not suitable for application for large image display apparatuses.

Japanese Patent Application Laid-Open No. 2000-338329 discloses a PVA film layer having a thickness of 6-30 μm on one side of a thermoplastic resin, which is stretched 2-5 times, or bonded to the other side of the PVA film layer. The method of manufacturing the polarizer which is 2-5 micrometers in thickness thin, and is free of curl and deformation by extending | stretching the conjugate | zygote of a layer structure 2-5 times is disclosed. In addition, Japanese Patent Application Laid-Open Nos. 2001-343521 and 2001-350021 apply a PVA-based solution to a base film, and uniaxially stretch in the longitudinal direction or the width direction, and the thickness of the base film is peeled off during the dyeing step. Disclosed is a method of manufacturing a polarizer having a size of 5-10 μm. However, such a method requires a thermoplastic resin or a base film, and additional processes such as peeling them off after the stretching step are not useful as a method of continuously manufacturing polarizers.

As described above, according to the manufacturing method of the conventional polarizer, it is difficult to continuously manufacture the thin polarizer that can be applied to both small and medium sized and large image display devices in an economical and stable manner.

The present invention provides a method of manufacturing a thin polarizer that can be continuously manufactured in a stable and economical way a thin polarizer capable of achieving light weight and thinning when applied to various image display devices without maintaining easily the optical characteristics For the purpose of

In addition, another object of the present invention is to provide a thin 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 thin polarizer.

The present invention comprises a first drawing step of stretching the polyvinyl alcohol-based film in the transverse direction (width direction) at a transverse stretching ratio of 1.30 to 1.90 times; 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 draw ratio of 5.00 to 7.20 times.

In addition, the present invention provides a thin 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 thin 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, it can be applied to both small and medium sized and large sized image display devices without being easily broken while maintaining the optical characteristics, and thus it is lightened when applied to polarizing plates and various image display devices. Thin polarizers capable of achieving thinning can be continuously manufactured in a stable and economic manner.

The present invention relates to a method of manufacturing a thin polarizer, a thin polarizer, and a polarizing plate provided with the same, which can achieve light weight and thinness when applied to various image display apparatuses.

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

The method for producing a thin polarizer of the present invention comprises a first stretching step of dry stretching a polyvinyl alcohol-based film at a transverse stretching ratio of 1.30 to 1.90 times in the transverse direction (width direction); And a second drawing step of wet drawing the polyvinyl alcohol-based film that has been stretched in the longitudinal direction (length direction) at a longitudinal draw ratio of 5.00 to 7.20 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 manufacturing method of a PVA system film is not specifically limited, For example, the flow cast method, the cast method, the extrusion method, etc. which form a film by flow-casting the polymer stock solution decomposed in water or an organic solvent are mentioned. 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 when 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 thin polarizing plate of this invention is the hybrid extending | stretching method which mixed the dry extending | stretching method and the wet extending | stretching method, It is especially the extending | stretching method using biaxial stretching of dry transverse stretching and wet longitudinal stretching.

In the method of manufacturing a thin polarizer according to an embodiment of the present invention, as shown in FIG. 2, a first stretching step (dry lateral stretching) performed before the swelling step and a second stretching performed after the first stretching step Step (wet longitudinal stretching).

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, that is, the lateral draw ratio, is preferably 1.30 to 1.90 times, more preferably 1.50 to 1.90 times. When the lateral stretch ratio is less than 1.30 times, the stretching effect is insignificant, making it difficult to obtain a thin polarizing plate having a desired thickness, and when it exceeds 1.90 times, it is difficult to maintain optical properties such as polarization degree.

The first stretching step is preferably performed before the swelling step, and may be performed by passing the PVA-based film at a constant speed between heating rolls or by pulling the PVA-based film in the width direction by using a tender 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 5.00 to 7.20 times, more preferably 5.50 to 6.50 times. If the stretching ratio is less than 5.00 times, the stretching effect is insignificant to obtain a thin polarizing plate having a desired thickness, and if it exceeds 7.20 times, it is difficult to maintain the degree of polarization and the polarizer 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 stretching step may be performed together with the swelling step, wherein the longitudinal draw ratio is preferably 1.10 to 3.50 times, more preferably 1.20 to 2.20 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, 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 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 stretching step may be performed together with the dyeing step, in which case the longitudinal drawing ratio is preferably 1.10 to 3.00 times, preferably 1.30 to 2.10 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 10% by weight relative to 100% by weight of the aqueous solution for crosslinking. 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 5.00 times, and the cumulative longitudinal draw ratio is preferably 5.00 to 7.20 times.

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 second drawing step may be stretched such that the total longitudinal drawing ratio is 5.00 to 7.20 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 potassium 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 invention, the value of the product of the lateral draw ratio and the longitudinal draw ratio of the first draw step and the second draw step is referred to as "stretch ratio", and the draw ratio is preferably 6.50 to 13.68 times, more preferably 8.90 to 12.00 times. Within this range, the thin polarizer can be manufactured while maintaining the optical properties.

As described above, according to the biaxial stretching method of the dry transverse stretching step of the first stretching step and the wet longitudinal stretching of the second stretching step, it is possible to secure a sufficient stretching ratio as a polarizer while applying less tension to the PVA-based film. It is possible to continuously manufacture a thin polarizer having a thin thickness of 15㎛ but not easily broken and can maintain optical characteristics.

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 ° C. 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.

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

It is preferable that the thickness of a thin polarizer is 5-15 micrometers. In the case of such a thickness, deterioration of mechanical strength and optical properties can be prevented, and weight reduction and thinning can be achieved while maintaining optical properties when applied to a polarizing plate or an image display device.

The transmittance of the thin polarizer is preferably 37.0% or more, more preferably 37.0 to 45.0%, and most preferably 40.0 to 45.0%.

It is preferable that the orthogonal transmittance measured at the conditions which overlapped two sheets so that the absorption axes of a thin polarizer cross each other by 90 degrees is low, More preferably, it is 0.030% or less, Most preferably, it is 0.020% or less.

Moreover, it is preferable that polarization degree is 97.00%-100%, More preferably, it is 98.50-100%.

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

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

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, water shielding, isotropy, etc. may be used, and specific examples thereof include polyethylene terephthalate, polyethylene isophthalate, polyethylene naphthalate, polybutylene terephthalate, and the like. Polyester film; 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; Polyoxy methylene 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), and the retardation (phase retardation) value Rth represented by is preferably -90 to +75 nm, more preferably -80 to +60 nm, and most preferably -70 to +45 nm. 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 thin polarizer 3 is manufactured by the polarizer manufacturing method of this invention, and is a polarizer whose thickness is 5-15 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 1.50 times dry stretched in the transverse direction on a heating roll at 95 ° C. The dry transversely stretched PVA film was swelled by dipping in a swelling tank filled with deionized water at 30 ° C. for 2 minutes, and then dyed by dipping for 4 minutes in an aqueous solution for dyeing at 30 ° C. containing 0.04% by weight of iodine and 1.19% by weight of potassium iodide. It was crosslinked by immersion for 1 minute in an aqueous solution for crosslinking at 55 ° C. containing 9.90% by weight of potassium iodide and 3.38% by weight of boric acid. At this time, in the swelling, dyeing and crosslinking step, the longitudinal stretching ratios were 1.50 times, 1.50 times, and 2.70 times, so that the PVA films were wet-stretched a total of 6.08 times in the longitudinal direction. When the above steps were completed, the PVA film was dried in an oven at 80 ° C. for 2 minutes to prepare a thin polarizer.

Example 2

The same process as in Example 1, but dry stretching in the transverse direction 1.50 times, and in the swelling, dyeing and cross-linking step, each longitudinal draw ratio is 1.50 times, 1.60 times, 2.95 times, the total wetted 7.08 times in the longitudinal direction Stretched.

Example 3

The same procedure as in Example 1 was carried out, but the film was stretched by 1.90 times in the transverse direction at 120 ° C.

Comparative Example 1

PVA film (VF-PS, KURARAY Co., Ltd.) having a thickness of 75 μm was swelled by immersion for 2 minutes in a swelling tank filled with deionized water at 30 ° C., and dyed at 30 ° C. containing 0.04% by weight of iodine and 1.19% by weight of potassium iodide It was immersed for 4 minutes in an aqueous solution for dyeing and crosslinked by immersion for 1 minute in an aqueous solution for crosslinking at 55 ° C. containing 9.9% by weight of potassium iodide and 3.38% by weight of boric acid. At this time, the respective stretching ratios were 1.50 times, 1.55 times, and 2.60 times in the swelling, dyeing, and crosslinking stages, and total uniaxial stretching was 6.05 times in the longitudinal direction. Upon completion of the above steps, the PVA film was dried in an oven at 80 ° C. for 2 minutes to prepare a polarizer.

Comparative Example 2

The same process as in Example 1, except that the dry stretching in the transverse direction 1.50 times, the longitudinal stretching ratio in the swelling, dyeing and crosslinking step is 1.30 times, 1.55 times, 2.00 times, total wet in the longitudinal direction 4.03 times It was.

Comparative Example 3

The same process as in Example 1, but the dry stretching in the transverse direction 1.50 times, the longitudinal stretching ratio in each swelling, dyeing and crosslinking step is 1.50 times, 1.70 times, 2.95 times wet stretching in the longitudinal direction total 7.52 times It was.

Comparative Example 4

The same procedure as in Example 1, except that the dry stretching in the lateral direction 3.30 times, the longitudinal stretching ratio in each swelling, dyeing and cross-linking step is 1.30 times, 1.50 times, 2.60 times wet drawing in total longitudinal direction 5.07 times It was.

Test Example

The physical properties of the thin polarizers prepared in Examples and Comparative Examples were measured by the following method, 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) 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).

division Drawing method Elongation ratio Polarizer thickness
(Μm) Transmittance (%) % Polarization Lateral draw ratio Elongation ratio Example 1 Biaxial stretching 1.50 6.08 8.5 42.21 99.13 Example 2 Biaxial stretching 1.50 7.08 8.0 37.39 97.77 Example 3 Biaxial stretching 1.90 6.08 6.0 39.12 98.61 Comparative Example 1 Single axis stretching - 6.05 12.5 40.24 99.34 Comparative Example 2 Biaxial stretching 1.50 4.03 12.5 35.77 99.17 Comparative Example 3 Biaxial stretching 1.50 7.52 PVA fracture Comparative Example 4 Biaxial stretching 3.00 5.07 5.5 19.81 94.80

As shown in Table 1, the polarizers of Examples 1 to 3 manufactured by biaxial stretching according to the present invention was confirmed that the thickness of the polarizers were not broken while maintaining optical properties such as transmittance and polarization. In particular, the polarizer of Example 1 prepared through 1.50 times dry transverse stretching and 6.08 times wet longitudinal stretching, compared to the polarizer of Comparative Example 1 prepared by conventional uniaxial stretching, has a thickness of 30% or more and a transmittance of not less than equivalent. It showed more polarization degree and was more preferable.

On the other hand, the polarizer of Comparative Example 1 prepared by the conventional uniaxial stretching method is difficult to be applied as a thin polarizer, the polarizer of Comparative Example 2 or 4 in which the stretching ratio of dry transverse stretching or wet longitudinal stretching does not fall within the scope of the present invention And optical properties were not satisfied simultaneously, and the polarizer of Comparative Example 3 was broken.

As described above, the thin 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 light weight and thinning while maintaining optical characteristics. Applicable to various image display devices.

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

2 is a flow chart showing a manufacturing process of a thin polarizer according to an embodiment of the present invention,

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

Explanation of symbols on the main parts of the drawings

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

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

1: surface protective film 2: polarizer protective film

3: thin polarizer 4: adhesive layer

5: release film

Claims (10)

A first stretching step of dry stretching the polyvinyl alcohol-based film at a transverse stretching ratio of 1.30 to 1.90 times in the transverse direction (width direction); And A method of manufacturing a thin polarizer comprising a second stretching step of wet stretching a polyvinyl alcohol-based film stretched in the longitudinal direction (length direction) at a longitudinal draw ratio of 5.00 to 7.20 times. The method of claim 1, wherein the longitudinal draw ratio of the second stretching step is 5.50 to 6.50 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 or is performed in an independent second stretching step. The method of claim 1, wherein the draw ratio is 6.50 to 13.68 times. The manufacturing method of the thin polarizer of Claim 1 whose thickness of the produced polarizer is 5-15 micrometers. The thin polarizer manufactured by the manufacturing method of any one of Claims 1-6. The thin polarizer according to claim 7, wherein the thickness is 5 to 15 µm. A polarizing plate in which a polarizer protective film is laminated on at least one surface of the thin polarizer of claim 7. A liquid crystal display device comprising the polarizing plate of claim 9.

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