TW201527126A - Polarizing plate - Google Patents

Abstract

The present invention relates to a polarizing plate. Particularly, the present invention relates to a polarizing plate which is obtained by adhesion between a protection film and a polarizing device with a shrinking force of 3.5 N/2 mm or less in a MD direction via an adhesive layer with a thermal expansion coefficient of 250 ppm/K or less disposed between the protection film and the polarizing device, such that the thermal shock durability becomes dramatically excellent, and the possibility of generating cracks is obviously lowered when being exposed to a high-temperature or low-temperature environment. Preferably, the shrinking force of the polarizing device in a TD direction is 2.5 N/2 mm or less, and the thermal expansion coefficient of the adhesive layer is 200 ppm/K or less.

Description

Polarizer

The present invention relates to a polarizing plate.

The polarizing plate is useful as one of optical parts constituting a liquid crystal display device. The polarizing plate usually has a structure in which a protective film is formed on two areas of the polarizing element, and is attached to the liquid crystal display device. It is known that a protective film is provided only on one surface of a polarizing element, but in many cases, a protective film is not simply used on the other surface, but a layer having, for example, an optical function as another function is also used as a protective film. Further, as a method for producing 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 the film is widely used.

Usually, for the polarizing element, the protective film is bonded immediately after the above washing and drying. The reason for this is that the polarizing element after drying has the following problems, that is, the physical strength is weak, and if it is temporarily taken up, it is easy to be broken in the machine direction. Therefore, in general, a water-based adhesive which is a polyvinyl alcohol-based resin aqueous solution is applied to the polarizing element after drying, and the protective film is simultaneously bonded to both surfaces of the polarizing element by interposing the adhesive.

Since such a polarizing plate can be exposed to various temperature environments such as manufacturing steps, operations, transportation, and use environments, it is necessary to exhibit sufficient durability so that cracks such as cracks do not occur in such an environment.

Therefore, the polarizing plate is subjected to a thermal shock endurance test which is alternately exposed to a low-temperature environment and a high-temperature environment after the manufacture, and the thermal shock endurance test is usually performed by alternately exposing each of the low-temperature and high-temperature environments for 30 minutes. The hour is about one cycle and is about 200 cycles.

In order to pass the durability test conducted under such severe conditions for a long period of time, excellent thermal shock durability is required, but in the case of a usual polarizing plate, there is a difference in thermal expansion coefficient between the polarizing element and the protective film. The medium polarizing element has a problem of cracking.

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

A polarizing element, a polarizing plate, and an image display device excellent in durability and heat resistance are described in Korean Laid-Open Patent Publication No. 2010-0089793.

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

SUMMARY OF THE INVENTION An object of the present invention is to provide a polarizing plate which is remarkably improved in thermal shock durability and which can significantly reduce cracking of a polarizing element.

A polarizing plate which is a polarizing element having a contraction force of 3.5 N/2 mm or less in the MD direction and a protective film followed by an adhesive layer having a thermal expansion coefficient of 250 ppm/K or less interposed therebetween.

2. The polarizing plate of item 1, wherein the polarizing element has a contraction force in the TD direction of 2.5 N/2 mm or less.

3. The polarizing plate of item 1, wherein the contraction force in the MD direction of the polarizing element is 2.5 times or less the contraction force in the TD direction.

4. The polarizing plate according to 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 of item 1, wherein the thermal expansion coefficient of the adhesive layer is Below 200ppm/K.

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

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

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

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 a protective film is adhered 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 is necessary to exhibit sufficient durability so that it does not cause defects in such an environment. In the case of such a poor durability, there is a problem that the polarizing element is cracked under extreme conditions such as repeated exposure to a high temperature and a low temperature environment.

However, the polarizing plate of the present invention has a coefficient of thermal expansion (CTE) of 250 ppm/K or less by passing a polarizing element having a contraction force in the MD direction of 3.5 N/2 mm or less and a protective film via a Coefficient of Thermal Expansion (CTE) therebetween. The layer is followed by a significant improvement in thermal shock durability.

In the present specification, the MD direction means the traveling direction of the film in the manufacturing step of the polarizing element, and the TD direction means the direction perpendicular to the MD direction.

The polarizing element of the present invention is one in which a dichroic dye is adsorbed on an extended polyvinyl alcohol-based resin film and aligned.

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 another monomer copolymerizable therewith. Examples of the other monomer copolymerizable with vinyl acetate include an unsaturated carboxylic acid type, an unsaturated sulfonic acid type, an olefin type, a vinyl ether type, and an acrylamide type monomer having an ammonium group. Further, the polyvinyl alcohol-based resin may be modified, and for example, polyvinyl formal or polyvinyl acetal modified to an aldehyde may be used. The degree of saponification of the polyvinyl alcohol-based resin is usually 85 to 100 mol%, preferably 98 mol% or more. Further, the degree of polymerization of the polyvinyl alcohol-based resin is usually 1,000 to 10,000, preferably 1,500 to 5,000.

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

The polarizing element of the present invention is produced by a step of continuously uniaxially stretching a polyvinyl alcohol-based film on an aqueous solution, a step of dyeing and adsorbing with a dichroic dye, and a treatment with an aqueous solution of boric acid. The steps, and the steps of washing and drying.

The step of uniaxially stretching the polyvinyl alcohol-based film may be carried out before dyeing, may be carried out simultaneously with dyeing, or may be carried out after dyeing. When uniaxial stretching is performed after dyeing, it may be carried out before boric acid treatment or in boric acid treatment. Of course, it is also possible to carry out the uniaxial stretching in a plurality of stages. For single-axis extensions, rolls with different peripheral speeds or column rolls can be used. Further, the uniaxial extension may be a dry extension extending in the atmosphere, and may be in a state of being swollen by using a solvent. Extend the wet extension. The extension ratio is usually 4 to 8 times.

A step of dyeing the stretched polyvinyl alcohol-based film with a dichroic dye can be, for example, a method of immersing a polyvinyl alcohol-based film in an aqueous solution containing a dichroic dye. As the dichroic dye, iodine or a dichroic dye can be used. Further, the polyvinyl alcohol-based film is preferably immersed in water before being dyed to be swollen.

When iodine is used as the dichroic dye, a method in which a polyvinyl alcohol-based film is immersed in an aqueous solution for dyeing containing iodine and potassium iodide for dyeing can be usually used. Usually, the content of iodine in the aqueous solution for dyeing is 0.01 to 1 part by weight based on 100 parts by weight of water (distilled water), and the content of potassium iodide is 0.5 to 20 parts by weight based on 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 resin film is immersed in an aqueous solution containing a water-soluble dichroic dye and dyed is usually used. The content of the dichroic dye in the aqueous solution 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. The aqueous solution may also contain an inorganic salt such as sodium sulfate as a dyeing aid. The temperature of the dye aqueous solution used for dyeing is usually 20 to 80 ° C, and the immersion time in the aqueous solution is usually 10 to 1,800 seconds.

The step of subjecting the dyed polyvinyl alcohol-based film to boric acid treatment can be carried out by immersing in an aqueous solution containing boric acid. Usually, the content of boric acid in the aqueous solution containing boric acid may be 2 to 15 parts by weight, preferably 5 to 12 parts by weight, per 100 parts by weight of water. In the case where iodine is used as the dichroic dye, the aqueous solution containing boric acid preferably contains potassium iodide, and the content thereof is usually 0.1 to 15 parts by weight, preferably 5 to 12 parts by weight, per 100 parts by weight of the 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, more preferably 200 to 200. 400 seconds.

The polyvinyl alcohol-based film after boric acid treatment is usually washed with water and dried. The water washing treatment can be carried out by immersing the boric acid-treated polyvinyl alcohol-based film in water. Washing water temperature Usually 5 to 40 ° C, the immersion time is usually 1 to 120 seconds. After washing with water, it is dried, whereby a polarizing element can be obtained. The drying treatment can usually be carried out 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 contraction 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 is preferably 3.2 N/2 mm or less.

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

Further, it is preferable that the contraction force in the MD direction of the polarizing element of the present invention is 2.5 times or less the contraction force in the TD direction. At this time, the balance between the contraction force in the MD direction and the contraction force in the TD direction is excellent, the internal stress is uniformly eliminated, and the thermal shock durability is remarkably improved. Preferably, it is 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 repellency, and isotropic properties. For example, an acrylic resin film or a cellulose resin film may be used. At least one of various transparent resin films of the group consisting of a polyolefin resin film and a polyester resin film.

Specific examples of the protective film include an acrylic resin film such as poly(methyl) acrylate or poly(methyl) acrylate; polyethylene terephthalate and polyethylene isophthalate; Polyester resin film such as ester, polyethylene naphthalate or polybutylene terephthalate; cellulose resin film such as diethyl phthalocyanine or triethylene fluorene cellulose; polyethylene, polypropylene, and ring Department or A polyolefin-based resin film such as a polyolefin-based or ethylene-propylene copolymer having a decene-lowering structure is preferably an acrylic resin film in terms of improving thermal shock durability, but is not limited thereto.

Further, in terms of further improving the thermal shock durability of the adhesive layer in the subsequent step, the thermal expansion coefficient in the MD direction and the TD direction of the protective film of the present invention may be 15 to 70 ppm/K, respectively.

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

In order to improve the adhesion, the polarizing element and/or the protective film may be subjected to a surface treatment of a chemical treatment such as a primer treatment, a plasma treatment, a corona treatment, or the like, or a chemical treatment such as a saponification (alkali) treatment. The saponification (alkali) treatment may be immersed in an aqueous solution of a base such as sodium hydroxide or potassium hydroxide.

The layer is then placed between the polarizing element and the protective film to cause the layers to follow each other.

The adhesive layer of the present invention has a coefficient of thermal expansion of 250 ppm/K or less. In such a case, the polarizing element having a contraction force in the MD direction of 3.5 N/2 mm or less and the protective film are followed, and the thermal shock durability can be remarkably improved.

The thickness of the layer is not particularly limited and may be, for example, 0.01 to 10 μm, preferably 0.1 to 5 μm. When the thickness of the adhesive layer is 0.5 μm or less, there is a problem that the possibility of mixing bubbles in the subsequent layer is high, and when the thickness of the adhesive layer is 5 μm or more, there is a problem that the price rises.

The layer may be formed by applying a photocurable adhesive composition to at least one of the surfaces of the polarizing element and the protective film to adhere to each other, and exposing the applied adhesive composition.

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 the photoradical polymerizable compound is contained, the water resistance is lowered, and when the photocationic polymerizable compound is contained, the viscosity of the composition is increased, so that it is preferable to contain a photoradical polymerizable compound and Both photocationically polymerizable compounds.

Examples of the photoradical polymerizable compound include monofunctional and difunctional to hexafunctional monomers, and specific examples thereof include methyl (meth)acrylate and allyl methacrylate and (methyl). 2-ethoxyethyl acrylate, isodecyl (meth) acrylate, 2-dodecyl thioethyl 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, tetradecyl (meth) acrylate, phenoxyethyl (meth) acrylate, urethane acrylate, aminoethyl (meth) acrylate, (meth) acrylate Monofunctional monomer 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, bicyclo fentanyl Dicyclofentanyl di(meth)acrylate, caprolactone modified dicyclopentenyl (meth)acrylate, ethylene oxide modified di(meth)acrylate, isocyanuric acid Bis(2-hydroxyethyl) ester di(meth)acrylate, di(acryloxyethyl)isocyanurate, allylic cyclohexyl (meth)acrylate, dimethylol di Cyclopentane diacrylate, ethylene oxide modified hexahydrophthalic acid diacrylate, tricyclodecane dimethanol acrylate, neopentyl glycol modified trimethylolpropane diacrylate, adamantane II a difunctional monomer such as acrylate; trimethylolpropane tri(meth)acrylate, dipentaerythritol tri(meth)acrylate, propionic acid modified dipentaerythritol tri(meth)acrylic acid Ester, neopentyl alcohol tri(meth) acrylate, propylene oxide modified three Methylolpropane tri(meth)acrylate, tris(2-hydroxyethyl) isocyanurate tris(meth)acrylate, tris(propyleneoxyoxyethyl) isocyanurate, glycerol Trifunctional monomer such as acrylate; diglycerin tetra(meth)acrylate, neopentyltetrakis(meth)acrylate, di(trimethylolpropane)tetra(meth)acrylate, etc. Functional monomer; penta-functional monomer such as propionic acid modified dipentaerythritol penta (meth) acrylate; and hexafunctionality such as caprolactone modified dipentaerythritol hexa(meth) acrylate Monomers and the like are preferred among the monofunctional to trifunctional monomers. These may be used alone or in combination of two or more.

Specific preferred examples include monofunctional acrylates such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and hydroxybutyl (meth)acrylate; and isocyanuric acid bis(propylene decyloxy) Ethyl)ester, allylated cyclohexyl (meth)acrylate, dimethylol dicyclopentane diacrylate, ethylene oxide modified hexahydrophthalic acid diacrylate, tricyclic guanidine Difunctional acrylate such as alkane dimethanol acrylate; neopentyl alcohol tri(meth) acrylate, propylene oxide modified trimethylolpropane tri (meth) acrylate, isocyanuric acid tris (2-hydroxyethyl) A trifunctional acrylate such as an ester tri(meth)acrylate; a diglyceryl tetra(meth)acrylate, a tetrafunctional acrylate of pentaerythritol tetra(meth)acrylate, or the like.

Examples of the photocationic polymerizable compound include bisphenol type epoxy resins such as bisphenol A type epoxy resin and bisphenol F type epoxy resin; phenol novolak type epoxy resin, cresol novolac type epoxy resin, etc. Novolac type epoxy resin; aliphatic epoxy resin, alicyclic epoxy resin, naphthalene epoxy resin, polyfunctional epoxy resin, biphenyl type epoxy resin, epoxy propylene ether type epoxy resin, ring Oxypropyl acrylate type epoxy resin, epoxy propylamine type epoxy resin; alcohol type epoxy resin such as hydrogenated bisphenol A type epoxy resin; halogenated epoxy resin such as brominated epoxy resin; rubber modified amine base Acid ester resin, amine ester modified epoxy resin, epoxidized polybutadiene, epoxidized styrene-butadiene-styrene block copolymer, epoxy group-containing polyester resin, epoxy group-containing polyurethane An epoxy group-containing compound such as a resin or an epoxy group-containing acrylic resin; phenoxymethyloxetane, 3,3-bis(methoxymethyl)oxetane, 3,3- Bis(phenoxymethyl)oxetane, 3-ethyl-3-(phenoxy) Methyl)oxetane, 3-ethyl-3-(2-ethylhexyloxymethyl)oxetane, 3-ethyl-3-{[3-(triethoxy) Mercapto)propoxy]methyl}oxetane, phenol novolac oxetane, 1,4-bis{[(3-ethyl-3-oxetanyl)methoxy]- An oxocyclic butyl compound such as benzene. These may be used alone or in combination of two or more.

Preferred examples thereof include a bisphenol A type epoxy resin, an alicyclic epoxy resin, a polyfunctional epoxy resin, an oxetane resin, and the like.

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

The photopolymerization initiator is used to increase the efficiency of the hardening reaction, and examples thereof include acetophenone type, benzophenone type, and 9-oxygen sulfur. Photo-cationic polymerization initiators such as thioxanthone, benzoin, and benzoin alkyl ether; photocationic polymerization of aromatic diazonium salts, aromatic sulfonium salts, aromatic iodine salts, and benzoin sulfonates Starter and so on.

As a commercially available photoradical polymerization initiator, Ciba's darocur 1173, darocur 4265, darocur BP, darocur TPO, darocur MBF, iragacure 184, ilgacure 500, ilgacure 2959, ilgacure 754, ilgacure 651, Irgacure 369, ilgacure 907, ilgacure 1300, ilgacure 819, ilgacure 2022, irgacure 819DW, ilgacure 2100, ilgacure 784, ilgacure 250, etc., but are not limited thereto. These may be used alone or in combination of two or more.

Further, 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 Corporation), CPI-110A (San-Apro), etc. Not limited to this. These may be used alone or in combination of two or more.

The content of the photopolymerization initiator is not particularly limited, and may be, for example, 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 has excellent durability.

The method of 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 of using a photopolymerizable compound having a high glass transition temperature (Tg) or improving The amount of light is accumulated to increase the modulus of elasticity, thereby lowering the coefficient of thermal expansion and the like.

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

When the protective film is only applied to one side of the polarizing element, the remaining surface of the polarizing element may be subjected to surface treatment such as hard coating treatment, anti-reflection treatment, anti-blocking treatment, treatment for diffusion or anti-glare, as needed.

Further, in addition to the surface treatment on the other surface of the polarizing element to which the protective film is bonded, a surface treatment layer such as a hard coat layer, an antireflection layer, an antiglare layer, or an antistatic layer may be laminated as needed, and may be adhered. The agent layer further laminates an optical functional film.

The type of the optical functional film is not particularly limited, and examples thereof include a liquid crystal compound or a polymer compound thereof, which is equal to an optical compensation film in which the surface of the substrate is aligned, and a polarized light that penetrates and polarizes light of a certain polarization. A reflective polarizing separation film that reflects light, a retardation film containing a polycarbonate resin, a retardation film containing a cyclic polyolefin resin, an anti-glare function additional film having an uneven shape on the surface, and a surface anti-reflection treatment An additional film, a reflective film having a reflective function on the surface, a semi-transmissive reflective film having a reflective function and a penetrating function, and the like.

Moreover, the present invention provides an image display device including the above polarizing plate.

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

In the following, in order to facilitate the understanding of the present invention, the preferred embodiments of the present invention are intended to be illustrative of the present invention. The embodiments are merely illustrative of the invention and are not intended to limit the scope of the appended claims. Various changes and modifications of the embodiments are possible within the scope and the scope of the appended claims.

[Manufacturing example, manufacture of polarizing element]

A polyvinyl alcohol film (PS 7500, Kuraray Co., Ltd.) having an average degree of polymerization of 2,400 and a saponification degree of 99.9% or more and having a thickness of 75 μm was immersed in water (deionized water) at 30 ° C for 2 minutes to swell, and then contained therein. Dyeing was carried out by dipping for 4 minutes in an aqueous solution of iodine 3.5 mmol/L and 2% by weight of potassium iodide at 30 ° C for dyeing. Thereafter, the mixture was immersed in an aqueous solution for crosslinking in which 2% by weight of potassium iodide and 3.7 wt% of boric acid were added, and the mixture was crosslinked for 2 minutes.

Thereafter, it was washed with distilled water of 25 ° C for 20 seconds.

The cumulative elongation ratio to the respective swelling/dyeing/crosslinking/water washing stages was 5.5 times, and then heat treatment was performed at 70 ° C for 5 minutes to produce a polarizing element (Production Example 1).

The polarizing elements of Production Examples 2 to 8 were produced under the same conditions and procedures as in Production Example 1 except for the conditions described in Table 1 below.

Further, the polarizing element to be produced was cut to a size of 3.0 cm (MD) × 2 mm (TD) and 3.0 cm (TD) × 2 mm (MD), and then MD, TD was measured by DMA Q800 (Dynamic mechanical analyzer, TA). Contraction force (measurement conditions were measured from a normal temperature of 10 ° C per minute to 80 ° C, and a contraction force of 1 hour was measured at 80 ° C). At this time, in order to maintain the state in which the polarizing element was flattened before the measurement, the measurement was performed using a minimum Pre-load.

[Examples and Comparative Examples]

The composition of the composition and the content of the adhesive composition described in the following Table 2 were applied to both surfaces of the polarizing element so as to have a thickness of 2 μm, and then the corona-treated acrylic film (the PMMA film was not stretched, using a nip roll). The MD direction thermal expansion coefficient (59.4 ppm/K, TD direction thermal expansion coefficient: 53.6 ppm/K) was bonded to both, and UV curing was performed by a high pressure mercury lamp to produce a polarizing plate.

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

The thermal expansion coefficient of the acrylic film and the triacetyl cellulose film was cut at a size of 8.0 mm × 4.0 mm, and then measured by TMA (TA Corporation) (measurement conditions were raised from 30 ° C to 10 ° C per minute to 70 ° C. After °C, the coefficient of thermal expansion was confirmed by a gradient up to 70 °C.

[Experimental example]

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

The adhesive composition of the above Table 2 was applied to a non-corona treated cycloolefin polymer (COP) film (ZEON Corporation) by hard coating at a thickness of 30 μm, respectively, and a high-pressure mercury lamp (UVA cumulative light amount) was used. UV hardening was performed at 500 mJ/cm ² × 4 times.

Next, the 30 μm adhesive layer was peeled off from the COP film, and cut into a size of 8.0 mm × 4.0 mm, and then the coefficient of thermal expansion was measured by TMA (TA Corporation) (measurement conditions were raised from 30 ° C to 70 ° C per minute from 30 ° C) Thereafter, the coefficient of thermal expansion was confirmed by a gradient up to 70 °C.

(2) Thermal shock durability test

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

Next, it was allowed to stand at room temperature for 24 hours, and the polarizing plate was placed in a thermal shock oven (the temperature was alternately changed from -40 ° C to 85 ° C every 30 minutes, and 6 hours was 1 cycle), and it was confirmed whether or not the polarizing element was cracked with time.

Each of the examples and the comparative examples was tested for each of the five samples, and the number of cracks was calculated by totaling the number of cracks generated from the five samples.

Referring to Table 3 above, it was confirmed that the polarizing plates of Examples 1 to 12 were not cracked at all, or only a very small number of cracks were generated, and the thermal shock durability was remarkably excellent.

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

Claims (6)

A polarizing plate in which a polarizing element having a contraction force of 3.5 N/2 mm or less in the MD direction and a protective film are followed by an adhesive layer having a thermal expansion coefficient of 250 ppm/K or less interposed therebetween. The polarizing plate of claim 1, wherein the polarizing element has a contraction force in the TD direction of 2.5 N/2 mm or less. The polarizing plate of claim 1, wherein the contracting force in the MD direction of the polarizing element is 2.5 times or less the contraction force in the TD direction. The polarizing plate of the first aspect of the invention, wherein the protective film is an acrylic resin film, a polyester resin film, a cellulose resin film or a polyolefin resin film. The polarizing plate of claim 1, wherein the adhesive layer has a thermal expansion coefficient of 200 ppm/K or less. An image display device comprising the polarizing plate of any one of claims 1 to 5.