TWI647116B - Polarizer - Google Patents

Abstract

The invention relates to a polarizing plate.

The present invention relates to a polarizing element and a protective film having a shrinkage force in the MD direction of 3.5 N / 2 mm or less and a bonding layer having a thermal expansion coefficient of 250 ppm / K or less interposed therebetween, and the thermal shock durability is remarkable. Excellent polarizers with a significantly lower probability of cracking when exposed to high and low temperature environments.

Description

Polarizer

The invention relates to a polarizing plate.

A polarizing plate is useful as one of optical components constituting a liquid crystal display device. A polarizing plate generally has a structure having a protective film on two areas of a polarizing element, and is mounted on a liquid crystal display device. It is known that a protective film is provided only on one side of the polarizing element, but in many cases, it is not a simple protective film on the other side, but a layer that has, for example, an optical function and functions as a protective film and is bonded. In addition, as a method of manufacturing a polarizing element, a method of subjecting a uniaxially stretched polyvinyl alcohol-based resin film dyed with a dichroic dye to boric acid treatment, washing with water, and drying is widely used.

Generally, in a polarizing element, a protective film is bonded immediately after the above-mentioned water washing and drying. The reason for this is that the polarizer after drying has problems such as physical strength is weak, and if it is temporarily wound up, it is liable to crack in the processing direction. Therefore, usually, the polarizer after drying is immediately coated with a water-based adhesive as an aqueous solution of a polyvinyl alcohol resin, and the protective film is simultaneously bonded to both sides of the polarizer through the adhesive.

Since such a polarizing plate can be exposed to a variety of temperature environments such as manufacturing steps, operations, transportation, and use environments, it must show sufficient durability so that defects such as cracks do not occur in this environment.

Therefore, after manufacturing, the polarizing plate is subjected to a thermal shock endurance test that is alternately exposed to a low temperature environment and a high temperature environment. Such a thermal shock endurance test is usually performed by alternately exposing the low temperature and high temperature environments to each other for 30 minutes. As one cycle, it takes about 200 cycles.

In order to pass the long-term durability test under such severe conditions, excellent thermal shock durability is required, but in the case of a normal polarizing plate, the test may be caused by the difference in thermal expansion coefficient between the polarizing element and the protective film. The middle polarizing element has a problem of cracking.

Therefore, development of a polarizing plate having excellent thermal shock durability capable of suppressing such cracks has been sought, but the actual situation is that such a polarizing plate has not yet been developed.

Korean Publication No. 2010-0089793 describes a polarizing element, a polarizing plate, and an image display device that are excellent in durability and heat resistance.

[Patent Document 1] Korean Publication No. 2010-0089793

An object of the present invention is to provide a polarizing plate having significantly improved thermal shock durability and significantly reducing cracks in a polarizing element.

A polarizing plate comprising a polarizer and a protective film having a contraction force of 3.5 N / 2 mm or less in the MD direction and a protective film with a thermal expansion coefficient of 250 ppm / K or less interposed therebetween.

2. The polarizing plate according to item 1 above, wherein the contraction force in the TD direction of the polarizing element is 2.5 N / 2 mm or less.

3. The polarizing plate according to the above item 1, wherein the shrinkage force in the MD direction of the polarizer is 2.5 times or less the shrinkage force in the TD direction.

4. The polarizing plate according to the above item 1, wherein the protective film is an acrylic resin film, a polyester resin film, a cellulose resin film, or a polyolefin resin film.

5. The polarizing plate according to the above item 1, wherein the thermal expansion coefficient of the adhesive layer is 200ppm / K or less.

6. An image display device comprising the polarizing plate according to any one of items 1 to 5.

The polarizing plate of the present invention is remarkably excellent in thermal shock durability. Therefore, when exposed to high and low temperature environments, the probability of cracks is also significantly lower.

The present invention relates to a polarizing plate, which is bonded by a polarizing element with a shrinkage force in the MD direction of 3.5 N / 2 mm or less and a protective film through a bonding layer with a thermal expansion coefficient of 250 ppm / K or less interposed therebetween. The impact durability is remarkably excellent. When exposed to high and low temperature environments, the probability of cracking is also significantly lower.

Hereinafter, the present invention will be described in detail.

A polarizing plate used for a liquid crystal display device or the like generally has a polarizing element made of a polyvinyl alcohol-based stretched film, and has a structure in which protective films are attached to both surfaces thereof.

Since such a polarizing plate can be exposed to various temperature environments such as manufacturing steps, operations, transportation, and use environments, it must show sufficient durability so that it will not cause defects in such an environment. In the case of such poor durability, there is a problem that cracks occur in the polarizing element under extreme conditions such as repeated exposure to high and low temperature environments.

However, in the polarizing plate of the present invention, the coefficient of thermal expansion (CTE) between the polarizing element and the protective film with a contraction force in the MD direction of 3.5 N / 2 mm or less is 250 ppm / K or less. The layers are bonded, and the thermal shock durability is significantly improved.

In this specification, the MD direction means the direction of travel of the film in the step of manufacturing the polarizing element, and the TD direction means a direction perpendicular to the MD direction.

The polarizing element-based dichroic dye of the present invention is obtained by adsorbing and aligning a stretched polyvinyl alcohol-based resin film.

The polyvinyl alcohol-based resin constituting the polarizing element can be obtained by saponifying a polyvinyl acetate-based resin. Examples of the polyvinyl acetate-based resin include polyvinyl acetate, which is a homopolymer of vinyl acetate, and a copolymer of vinyl acetate and other monomers copolymerizable therewith. Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acid based, unsaturated sulfonic acid based, olefin based, vinyl ether based, and acrylamide based monomers having an ammonium group. The polyvinyl alcohol-based resin may be modified, and for example, polyvinyl formal or polyvinyl acetal modified to aldehydes may be used. The saponification degree of the polyvinyl alcohol resin is usually 85 to 100 mol%, preferably 98 mol% or more. The polymerization degree of the polyvinyl alcohol resin is usually 1,000 to 10,000, and preferably 1,500 to 5,000.

Forming such a polyvinyl alcohol-based resin in the form of a film can be used as a disc film for a polarizing element. The method for forming a polyvinyl alcohol-based resin is not particularly limited, and a known method can be used. The film thickness of the disc film is not particularly limited, and may be, for example, 10 to 150 μm.

The polarizing element of the present invention is manufactured through the following steps: a step of uniaxially stretching a polyvinyl alcohol-based film on an aqueous solution, a step of dyeing and adsorbing a dichroic dye, and a treatment using an aqueous boric acid solution. Steps, and steps of washing and drying.

The step of uniaxially stretching the polyvinyl alcohol-based film may be performed before dyeing, may be performed simultaneously with dyeing, or may be performed after dyeing. When uniaxial stretching is performed after dyeing, it may be performed before or in a boric acid treatment. Of course, it is also possible to make these uniaxial extensions through multiple stages. Uniaxial extension can use rollers or rows of rollers with different peripheral speeds. In addition, the uniaxial stretching may be a dry stretching in the atmosphere, and may be in a state where it is swollen with a solvent. Wet extension is performed. The stretch ratio is usually 4 to 8 times.

For the step of dyeing the stretched polyvinyl alcohol-based film with a dichroic dye, for example, a method of dipping the polyvinyl alcohol-based film in an aqueous solution containing a dichroic dye can be used. As the dichroic dye, iodine or a dichroic dye can be used. The polyvinyl alcohol-based film is preferably swelled by being immersed in water before dyeing.

When using iodine as a dichroic dye, a method of dyeing a polyvinyl alcohol-based film by immersing it in an aqueous solution for dyeing containing iodine and potassium iodide can be generally used. Generally, the content of iodine in the dyeing aqueous solution is 0.01 to 1 part by weight with respect to 100 parts by weight of water (distilled water), and the content of potassium iodide is 0.5 to 20 parts by weight with respect to 100 parts by weight of water. The temperature of the aqueous solution for dyeing is usually 20 to 40 ° C, and the immersion time (dyeing time) is usually 20 to 1,800 seconds.

When a dichroic dye is used as the dichroic dye, a method in which a polyvinyl alcohol-based resin film is immersed in an aqueous solution containing a water-soluble dichroic dye is usually used for dyeing. Regarding the content of the dichroic dye in the aqueous solution, it is usually 1 × 10 ^-4 to 10 parts by weight, preferably 1 × 10 ^-3 to 1 part by weight per 100 parts by weight of water. This aqueous solution may contain an inorganic salt such as sodium sulfate as a dyeing aid. The temperature of the aqueous dye solution used for dyeing is usually 20 ~ 80 ° C, and the immersion time in the aqueous solution is usually 10 ~ 1,800 seconds.

The step of subjecting the dyed polyvinyl alcohol-based film to a boric acid treatment can be performed by immersing it in an aqueous solution containing boric acid. Generally, the content of boric acid in the boric acid-containing aqueous solution may be 2 to 15 parts by weight, and preferably 5 to 12 parts by weight relative to 100 parts by weight of water. When using iodine as a dichroic pigment, the boric acid-containing aqueous solution preferably contains potassium iodide, and its content is usually 0.1 to 15 parts by weight, and preferably 5 to 12 parts by weight relative to 100 parts by weight of water. The temperature of the aqueous solution containing boric acid is usually 50 ° C or higher, preferably 50 to 85 ° C, more preferably 60 to 80 ° C, and the immersion time is usually 60 to 1,200 seconds, preferably 150 to 600 seconds, and more preferably 200 to 400 seconds.

Polyvinyl alcohol film after boric acid treatment is usually washed and dried. The water washing treatment can be performed by immersing a boric acid-treated polyvinyl alcohol-based film in water. Water temperature for washing treatment It is usually 5 to 40 ° C, and the immersion time is usually 1 to 120 seconds. After washing with water and drying, a polarizing element can be obtained. The drying process can usually be performed using a hot-air dryer or a far-infrared heater. The drying treatment temperature is usually 30 to 100 ° C, preferably 50 to 80 ° C, and the drying time is usually 60 to 600 seconds, preferably 120 to 600 seconds.

The thickness of the polarizing element of the present invention is not particularly limited, and may be, for example, 5 to 40 μm.

The shrinkage force in the MD direction of the polarizing element of the present invention is 3.5 N / 2 mm or less. When the shrinkage force in the MD direction is within the above range, the thermal shock durability is excellent when applied to a polarizing plate. In this respect, it may be preferably 3.2 N / 2 mm or less.

The polarizing element extends in the MD direction and most of it shrinks in the MD direction. Therefore, it is understood that the crack of the polarizing element is mainly related to the shrinking force in the MD direction. However, it is found that in the present invention, when the shrinkage force in the TD direction is 2.5 N / 2 mm or less, the thermal shock durability is further improved. Therefore, the shrinkage force in the TD direction is more preferably 2.5N / 2mm or less, but it is not limited thereto.

The shrinkage force in the MD direction of the polarizing element of the present invention may be 2.5 times or less the shrinkage force in the TD direction. At this time, the balance between the shrinkage force in the MD direction and the shrinkage force in the TD direction is excellent, the internal stress is uniformly eliminated, and the thermal shock durability is significantly improved. It is preferably 1 to 2.3 times.

The type of the protective film is not particularly limited as long as it is excellent in transparency, mechanical strength, thermal stability, water resistance, and isotropic properties. For example, it may be selected from the group consisting of acrylic resin films and cellulose resin films. Various transparent resin films of at least one of the group consisting of a polyolefin resin film and a polyester resin film.

Specific examples of the protective film include acrylic resin films such as poly (meth) acrylate and poly (meth) acrylate; polyethylene terephthalate and polyethylene isophthalate. Polyester resin films such as polyester, polyethylene naphthalate, polybutylene terephthalate; cellulose resin films such as diethyl cellulose and triethyl cellulose; polyethylene, polypropylene, Department or In terms of improving thermal shock durability, a polyolefin resin film such as a polyolefin resin having a norbornene structure and an ethylene-propylene copolymer is preferably an acrylic resin film, but it is not limited thereto.

In addition, from the viewpoint of further improving the thermal shock durability of the above-mentioned adhesive layer at the time of adhering, the thermal expansion coefficients of the MD direction and the TD direction of the protective film of the present invention are preferably 15 to 70 ppm / K, respectively.

The thickness of the protective film is not particularly limited, and may be 10 to 200 μm, and preferably 10 to 150 μm. In the case where the thickness of the protective film is 10 to 200 μm, when the two-layer layer polarizing element protective film of the polarizing element is used, each protective film may have the same thickness or different thickness from each other.

In order to improve the adhesion, the polarizing element and / or the protective film may be subjected to surface treatments such as primer coating treatment, plasma treatment, corona treatment, and other dry treatments, and chemical treatments such as saponification (alkali) treatment. Examples of the saponification (alkali) treatment include a method of immersion in an aqueous solution of an alkali such as sodium hydroxide or potassium hydroxide.

Then, the layer is interposed between the polarizing element and the protective film so that these are adhered to each other.

The thermal expansion coefficient of the adhesive layer of the present invention is 250 ppm / K or less. In this case, a polarizing element with a shrinkage force in the MD direction of 3.5 N / 2 mm or less and a protective film can significantly improve the thermal shock durability.

The thickness of the adhesion layer is not particularly limited, and may be, for example, 0.01 to 10 μm, and preferably 0.1 to 5 μm. When the thickness of the adhesive layer is 0.5 μm or less, there is a problem that bubbles are likely to be mixed during the adhesion, and when the thickness of the adhesive layer is 5 μm or more, there is a problem that the price rises.

The adhesive layer may be formed by applying a photocurable adhesive composition to at least one of the mutually adhering surfaces of the polarizing element and the protective film, adhering these, and exposing the applied adhesive composition to light.

The photocurable adhesive composition contains a photopolymerizable compound and a photopolymerization initiator.

The photopolymerizable compound may be at least one of a photoradical polymerizable compound and a photocationic polymerizable compound.

When only a photoradically polymerizable compound is contained, water resistance is reduced, and when only a photocationically polymerizable compound is contained, the viscosity of the composition is increased. Therefore, it is preferable to contain a photoradically polymerizable compound and Both photocationically polymerizable compounds.

Examples of the photoradically polymerizable compound include monofunctional and difunctional to hexafunctional monomers, and specifically, methyl (meth) acrylate, allyl methacrylate, and (meth) 2-ethoxyethyl acrylate, isodecyl (meth) acrylate, 2-dodecylthioethyl methacrylate, octyl acrylate, 2-methoxyethyl acrylate, hydroxyl (meth) acrylate Ethyl ester, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, isooctyl (meth) acrylate, isodecyl (meth) acrylate, stearyl (meth) acrylate, methyl Glycidyl acrylate, tetrafurfuryl (meth) acrylate, phenoxyethyl (meth) acrylate, urethane acrylate, aminoethyl (meth) acrylate, dimethacrylate Monofunctional monomers such as methylaminoethyl ester; 1,3-butanediol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, 1,6-hexanediol Di (meth) acrylate, ethylene glycol di (meth) acrylate, bisphenol A-ethylene glycol diacrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (methyl) )acrylic acid , Polyethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, dipropylene glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate, dicyclofentanyl di (Meth) acrylate (dicyclofentanyl di (meth) acrylate), caprolactone modified dicyclomethenyl di (meth) acrylate, ethylene oxide modified phosphate di (meth) acrylate, isocyanuric acid Bis (2-hydroxyethyl) ester di (meth) acrylate, bis (acryloxyethyl) isocyanurate, cyclohexyl bis (meth) acrylate, dimethylol bis Cyclopentane diacrylate, ethylene oxide modified hexahydrophthalic acid diacrylate, tricyclodecane dimethanol acrylate, neopentyl glycol modified trimethylolpropane diacrylate, adamantane di Difunctional monomers such as acrylates; trimethylolpropane tri (meth) acrylate, dipentaerythritol tri (meth) acrylate, propionic acid modified dipentaerythritol tri (meth) acrylic acid Ester, neopentaerythritol tri (meth) acrylate, propylene oxide modified three Methylolpropane tri (meth) acrylate, tris (2-hydroxyethyl) isocyanurate tris (meth) acrylate, tris (acryloxyethyl) isocyanurate, tris (glycerol) Trifunctional monomers such as acrylate; bisglycerol tetra (meth) acrylate, neopentyl tetraol (meth) acrylate, bis (trimethylolpropane) tetra (meth) acrylate, etc. Functional monomers; pentafunctional monomers such as propionic acid modified dipentaerythritol penta (meth) acrylate; and caprolactones modified hexafunctional such as dipentaerythritol hexa (meth) acrylate Monomers and the like are preferably monofunctional to trifunctional monomers. These can be used individually or in mixture of 2 or more types.

Preferred specific examples include monofunctional acrylates such as hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, and hydroxybutyl (meth) acrylate; and bis (acryloxy) isocyanurate Ethyl) esters, allyl cyclohexyl di (meth) acrylate, dimethylol dicyclopentane diacrylate, ethylene oxide modified hexahydrophthalate diacrylate, tricyclodecane Difunctional acrylates such as alkanedimethanol acrylate; neopentyl tetraol tri (meth) acrylate, propylene oxide modified trimethylolpropane tri (meth) acrylate, isocyanuric tris (2-hydroxyethyl) Trifunctional acrylates such as tris (meth) acrylates; bisglycerol tetra (meth) acrylates, tetrafunctional acrylates of neopentaerythritol tetra (meth) acrylates, and the like.

Examples of the photocationically polymerizable compound include bisphenol epoxy resins such as bisphenol A epoxy resin and bisphenol F epoxy resin; phenol novolac epoxy resin, cresol novolac epoxy resin, etc. Novolac epoxy resins; aliphatic epoxy resins, alicyclic epoxy resins, naphthalene epoxy resins, polyfunctional epoxy resins, biphenyl epoxy resins, propylene oxide epoxy resins, ring Oxypropyl ester epoxy resin, epoxy amine epoxy resin; hydrogenated bisphenol A epoxy resin and other alcohol epoxy resin; brominated epoxy resin and other halogenated epoxy resin; rubber modified amino methyl Ester resin, amine ester modified epoxy resin, epoxidized polybutadiene, epoxidized styrene-butadiene-styrene block copolymer, epoxy resin containing polyester resin, epoxy resin containing polyurethane Resins, epoxy-containing acrylic resins and other epoxy-containing compounds; phenoxymethyloxetane, 3,3-bis (methoxymethyl) oxetane, 3,3- Bis (phenoxymethyl) oxetane, 3-ethyl-3- (phenoxy Methylmethyl) oxetane, 3-ethyl-3- (2-ethylhexyloxymethyl) oxetane, 3-ethyl-3-{[3- (triethoxy Silyl) propoxy] methyl} oxetane, phenol novolac oxetane, 1,4-bis {[(3-ethyl3-oxetanyl) methoxy] methyl An oxetanyl compound such as benzene and the like. These can be used individually or in mixture of 2 or more types.

Preferred specific examples include bisphenol A epoxy resin, alicyclic epoxy resin, polyfunctional epoxy resin, and oxetane resin.

When the photopolymerizable compound contains both a photoradical polymerizable compound and a photocationic polymerizable compound, the mixing ratio of these is not particularly limited. For example, the photocationic polymerizable compound may be included in the total weight of all polymerizable compounds. Contains 50% by weight or more. In this case, since the thermal expansion coefficient of the adhesive layer becomes low, the thermal shock durability is excellent.

Photopolymerization initiators are used to improve the efficiency of the curing reaction, and examples include acetophenone-based, benzophenone-based, and 9-oxysulfur. (thioxanthone) -based, benzoin-based, benzoin alkyl ether-based photoradical polymerization initiators; aromatic diazonium salts, aromatic sulfonium salts, aromatic aluminum iodonium salts, and benzoin sulfonate photopolymerize Starting agent and so on.

Examples of commercially available photo-radical polymerization initiators include darocur 1173, darocur 4265, darocur BP, darocur TPO, darocur MBF, irgacure 184, irgacure 500, irgacure 2959, irgacure 754, irgacure 651, Ciba Irgacure 369, irgacure 907, irgacure 1300, irgacure 819, irgacure 2022, irgacure 819DW, irgacure 2100, irgacure 784, irgacure 250, etc. are not limited thereto. These can be used individually or in mixture of 2 or more types.

Examples of the photocationic polymerization initiator include Optomer-SP-151, Optomer-SP-170, Optomer-SP-171 (ADEKA), Irgacure-261 (Ciba), San-Aid SI-60L, UVI-6990 (Union Carbide), BBI-1C3, MPI-103, TPS-103, DTS-103, NAT-103, NDS-103 (Green Chemical), CPI-110A (San-Apro), etc., but Not limited to these. These can be used individually or in mixture of 2 or more types.

The content of the photopolymerization initiator is not particularly limited. For example, it may contain 0.5 to 10 parts by weight based on 100 parts by weight of the photopolymerizable compound. When the content is within the above range, it has an appropriate hardening speed and excellent durability.

The method for adjusting the thermal expansion coefficient of the adhesive layer to 250 ppm / K or less is not particularly limited, and a method known in the art can be used. For example, a method such as using a photopolymerizable compound having a high glass transition temperature (Tg) or increasing the temperature can be used. The amount of light is accumulated to increase the elastic modulus, thereby reducing the thermal expansion coefficient and the like.

In the polarizing plate of the present invention, the protective film is attached to at least one side of the polarizing element, and may be attached to one or both sides of the polarizing element.

When the protective film is only attached to one side of the polarizing element, the remaining surface of the polarizing element may be appropriately subjected to surface treatments such as hard coating treatment, anti-reflective treatment, anti-blocking treatment, and treatment for the purpose of diffusion or anti-glare.

Furthermore, in addition to the surface treatment described above, the other side of the polarizing element with a protective film bonded to one side may be further laminated with a surface treatment layer such as a hard coat layer, an anti-reflection layer, an anti-glare layer, or an anti-static layer, if necessary. The agent layer is further laminated with an optically functional film.

The type of the optically functional film is not particularly limited, and examples thereof include an optical compensation film having a liquid crystal compound or a polymer compound equal to the surface alignment of the substrate, a type of polarized light that penetrates, and a polarized light of the opposite property. Reflection type polarizing separation film with light reflection, retardation film containing polycarbonate resin, retardation film containing cyclic polyolefin resin, anti-glare function additional film with uneven shape on the surface, surface anti-reflection treatment Additional films, reflective films with reflective functions on the surface, and semi-transparent reflective films with both reflective and penetrating functions.

The present invention also provides an image display device including the polarizing plate.

The polarizing plate of the present invention can be applied not only to ordinary liquid crystal display devices, but also to various image display devices such as electric field light emitting display devices, plasma display devices, and field emission display devices.

In the following, preferred embodiments are shown in order to help the understanding of the present invention, but the industry understands that these embodiments are merely examples of the present invention and do not limit the scope of the accompanying patent application. Various changes and amendments are made to the implementation within the scope, and of course such changes and amendments belong to the scope of the accompanying patent application.

[Manufacture example, manufacture of polarizing element]

A 75 μm-thick polyvinyl alcohol film (PS 7500, Kuraray) having an average degree of polymerization of 2,400 and a degree of saponification of 99.9% or more was immersed in water (deionized water) at 30 ° C. for 2 minutes to swell it. The dyeing solution was immersed in a 30 ° C. dyeing aqueous solution for 3.5 minutes with 3.5 mmol / L of iodine and 2% by weight of potassium iodide to dye. Thereafter, it was immersed in a 53 ° C. aqueous solution for crosslinking to which 2% by weight of potassium iodide and 3.7% by weight of boric acid were added for 2 minutes to crosslink.

After that, it was washed with distilled water at 25 ° C for 20 seconds.

The cumulative elongation ratio at each swelling / dyeing / crosslinking / washing stage was 5.5 times, followed by heat treatment at 70 ° C for 5 minutes to manufacture a polarizing element (Production Example 1).

The polarizing elements of Manufacturing Examples 2 to 8 were manufactured under the same conditions and steps as those of Manufacturing Example 1 except for the conditions described in Table 1 below.

Then, the manufactured polarizing elements were cut at a size of 3.0 cm (MD) x 2 mm (TD) and 3.0 cm (TD) x 2 mm (MD), and then MD and TD were measured using a DMA Q800 (Dynamic mechanical analyzer, TA). Shrinking force (measurement conditions are measured at room temperature from 10 ° C to 80 ° C per minute, and then the shrinking force is measured at 80 ° C for one hour). At this time, in order to maintain the state where the polarizing element is flattened before the measurement, the measurement is performed using a minimum pre-load.

[Examples and Comparative Examples]

The adhesive composition having the composition and content described in Table 2 below was applied to both sides of the polarizing element so that the thickness became 2 μm, and then the corona-treated acrylic film (unextended PMMA film, The thermal expansion coefficient in the MD direction is 59.4 ppm / K, and the thermal expansion coefficient in the TD direction is 53.6 ppm / K). The polarizing plate is manufactured by UV curing using a high-pressure mercury lamp.

In the case of Example 9, the above-mentioned acrylic film was bonded to one surface of the polarizing element, and a triethylfluorene cellulose film was bonded to the other surface (MD direction thermal expansion coefficient 20.7 ppm / K, TD direction thermal expansion coefficient 22.1 ppm / K).

The thermal expansion coefficients of the acrylic film and triacetam cellulose film were cut at a size of 8.0 mm × 4.0 mm, and then measured by TMA (TA company) (the measurement conditions were that the temperature was raised from 70 ° C. to 70 ° C. per minute from 30 ° C.). After the temperature, the thermal expansion coefficient was confirmed with a gradient up to 70 ° C).

[Experimental example]

(1) Thermal expansion coefficient (CTE) of the bonding layer

After applying the adhesive composition of Table 2 to a thickness of 30 μm by hard coating on one piece of cyclic olefin polymer (COP) film (ZEON) without corona treatment, a high-pressure mercury lamp (UVA cumulative light amount) was used. 500 mJ / cm ² × 4 times) for UV curing.

Next, the 30 μm adhesive layer was peeled from the COP film and cut to a size of 8.0 mm × 4.0 mm, and then the thermal expansion coefficient was measured by TMA (TA) (the measurement conditions are that the temperature is raised from 10 ° C to 70 ° C per minute from 30 ° C) Then, the thermal expansion coefficient was confirmed with a gradient to 70 ° C).

(2) Thermal shock durability test

The polarizing plates manufactured in the examples and comparative examples were cut at a size of 15.0 cm (MD) x 11 cm (TD), and then bonded to glass with an acrylic adhesive composition, and then subjected to an autoclave treatment (50 ° C, 20 minutes, 5 atmospheres).

Next, it was left at room temperature for 24 hours, and the polarizing plate was put into a thermal shock oven (the temperature was changed from -40 ° C to 85 ° C alternately every 30 minutes, and 6 hours was a cycle), and it was confirmed whether the polarizing element cracked with time.

In each of the examples and comparative examples, experiments were performed on 5 samples each, and the number of cracks was calculated by totalizing the number of cracks generated from the 5 samples.

With reference to Table 3 above, it was confirmed that the polarizing plates of Examples 1 to 12 did not generate cracks at all, or generated only a very small number of cracks, and were extremely excellent in thermal shock durability.

However, the polarizing plates of Comparative Examples 1 to 3 generated a large number of cracks, and the thermal shock durability was poor.

Claims (5)

A polarizing plate having a light-curing property of a polyvinyl alcohol-based polarizing element and a protective film having a shrinkage force of 3.5 N / 2 mm or less and a thickness of 5 to 40 μm in the MD direction, with a thermal expansion coefficient of 250 ppm / K or less interposed therebetween The layer is followed by a layer; the thickness of the protective film is 10 to 200 μm, and is an acrylic resin film, a polyester resin film, a cellulose resin film, or a polyolefin resin film; the thickness of the adhesive layer is 0.01 to 10 μm. For example, the polarizing plate of the first patent application range, wherein the contraction force of the polarizing element in the TD direction is 2.5N / 2mm or less. For example, the polarizing plate of the first scope of the patent application, wherein the shrinkage force in the MD direction of the polarizer is less than 2.5 times the shrinkage force in the TD direction. For example, the polarizing plate of the first scope of the patent application, wherein the thermal expansion coefficient of the adhesive layer is 200 ppm / K or less. An image display device includes a polarizing plate according to any one of claims 1 to 4.