KR20210027813A - Polarizing plate and image display apparatus comprising same - Google Patents

Abstract

The present specification relates to a polarizing plate comprising a polarizer and a hard coating layer provided on one or both surfaces of the polarizer, and an image display device including the same. When the polarizing plate is applied to the image display device, excellent optical properties can be maintained under high temperature or high humidity conditions.

Description

A polarizing plate and an image display device including the same TECHNICAL FIELD [POLARIZING PLATE AND IMAGE DISPLAY APPARATUS COMPRISING SAME}

The present specification relates to a polarizing plate and an image display device including the same.

Conventional polarizing plates for liquid crystal display devices use a general polyvinyl alcohol (PVA)-based polarizer, and a protective film such as polyethylene terephthalate (PET) is attached to at least one side of the polarizer through an adhesive. It is composed of.

In order to apply various protective films, curing systems are also applied in various ways, and long wavelength curing systems are being introduced. At this time, it is necessary to include a photosensitizer of a long wavelength region in the adhesive composition for curing with a long wavelength.

However, the photosensitizer in the long wavelength region basically has a yellowish property, and has a problem that deviates from the optical properties required of a polarizing plate.

In order to prevent the yellowing phenomenon, a method of lowering the KI concentration of the dyeing bath or lowering the drying temperature of the polarizing element during the stretching process of the polarizer is being studied. There is.

There is a need for a method for suppressing the yellowing phenomenon of the adhesive itself in the adhesive layer.

Korean Patent Application Publication 2016-0142546

An object of the present specification is to provide a polarizing plate and an image display device including the same.

The present specification provides a polarizing plate including a polarizer and a hard coating layer provided on one or both surfaces of the polarizer, and wherein the hard coating layer satisfies the following relational expression.

[Relationship]

Yellowness of the hard coating layer (Y1) / the thickness of the hard coating layer ≤ 0.05 (㎛ ^-1 )

In addition, the present specification provides an image display device including the polarizing plate described above.

The present specification provides a polarizing plate having a thin thickness and suppressing yellowing.

In addition, the polarizing plate of the present specification provides a polarizing plate in which the yellowing phenomenon is suppressed under high temperature or high humidity conditions.

In addition, the polarizing plate of the present specification provides a polarizing plate having an improved polarizer protection effect under high temperature or high humidity conditions.

When the polarizing plate of the present specification is applied to an image display device, optical properties may be excellently maintained under high temperature or high humidity conditions.

1 illustrates a polarizing plate according to an exemplary embodiment of the present specification.
2 shows a polarizing plate according to another exemplary embodiment of the present specification.
3 illustrates a polarizing plate according to another exemplary embodiment of the present specification.

Hereinafter, the present specification will be described in more detail.

In the present specification, when a part "includes" a certain component, it means that other components may be further included rather than excluding other components unless otherwise stated.

In the present specification, when a member is said to be positioned "on" another member, this includes not only the case where the member is in contact with the other member, but also the case where another member exists between the two members.

In the present specification, “polarizing plate” refers to a laminate including “polarizer”, and the polarizing plate may include other configurations in addition to the polarizer. However, when the polarizing plate does not include a configuration other than the polarizer, the polarizing plate and the polarizer may be interpreted in the same manner.

When a protective film is directly formed on a polyvinyl alcohol-based polarizer of an existing polyvinyl alcohol-based stretch type, the polarizer is less torn due to stress caused by shrinkage of the polarizer at high temperature compared to the case of applying a protective substrate on both sides as before. It was difficult to solve the problem that occurred. In addition, in order to prevent the problem of deteriorating the optical properties of the polarizing plate due to the protective substrate, physical properties having no retardation and no yellowing have been required.

Therefore, in order to form a protective film directly on the polarizer, physical properties of a level capable of withstanding the stress caused by contraction of the polarizer at high temperatures are required. As a protective film that satisfies these physical properties, a UV-curable cationic coating layer is mainly used. In the case of a cationic coating layer, a photoinitiator and a photosensitizer are mainly used to improve the degree of curing, and in this process, the optical properties of the polarizing plate are deteriorated due to yellowing of the cured product.

The present specification provides a polarizing plate including a polarizer and a hard coating layer provided on one or both surfaces of the polarizer, and wherein the hard coating layer satisfies the following relational expression.

[Relationship]

Yellowness of the hard coating layer (Y1) / the thickness of the hard coating layer ≤ 0.05 (㎛ ^-1 )

In general, as the thickness of the hard coating layer increases, the yellowness of the hard coating layer also increases, resulting in a problem that the optical properties of the polarizing plate are deteriorated. In the present invention, even if the thickness of the hard coating layer is increased, the yellowness of the hard coating layer ^{is maintained within a certain range (0.05 µm -1} ) or less, thereby providing a polarizing plate that does not increase the yellowness of the hard coating layer even under high temperature or high humidity conditions.

The yellowness (Y1) refers to the yellowness of the hard coating layer when the polarizing plate or the hard coating layer is cured and left for 24 hours under a temperature condition of 25° C. and a relative humidity of 40%.

Alternatively, the yellowness (Y1) may mean a difference in yellowness before and after leaving the polarizing plate or the hard coating layer at a temperature of 25° C. and a relative humidity of 40% for 24 hours.

The above relational expression is a value obtained by dividing the yellowness value of the hard coating layer by the thickness of the hard coating layer. The yellowness refers to the b* value of the L*, a*, b* coordinate system, and the content of the coordinate system is described in the document IES type B Reference [IES-LM-75-01 Goniophotometer Types and Photometric Coordinates (title), IES. (author), (Illuminating Engineering Society of North America, 2001)]. The L*, a*, and b* values can be measured using a ray spectrometer (V-7100, manufactured by JASCO).

In addition, the thickness of the hard coating layer can be measured by measuring the cross section of the polarizing plate using a FESEM SU-8020 SYSTEM equipment (measurement conditions: acceleration voltage 2 kV, emission current: 10uA, working distance: 8mm, Detector: SE).

The relational expression is preferably the yellowness of the hard coating layer (Y1) / the thickness of the hard coating layer ≤ 0.04 (㎛ ^-1 ), more preferably the yellowness of the hard coating layer (Y1) / the thickness of the hard coating layer ≤ 0.03 (㎛ ^-1) ) Can be satisfied.

In order to satisfy the above relational expression, the yellowness (Y1) of the hard coating layer may be further lowered. As a method of lowering the yellowness of the hard coating layer, there is a method of changing the composition of the composition for forming the hard coating layer for forming the hard coating layer. If the yellowness of the hard coating layer is lowered, even if the thickness of the hard coating layer is increased, there is an advantage that optical properties are not impaired. Specifically, the yellowness (Y1) of the hard coating layer may be 0.3 or less, preferably 0.28 or less, and more preferably 0.25 or less. The lower limit of the yellowness (Y1) of the hard coating layer may be greater than 0.

Since the hard coating layer functions to protect other components, the higher the thickness, the better the protection function, but the optical properties may be deteriorated. Therefore, it is important to control the thickness within a certain range to ensure a protective function and prevent the optical properties from deteriorating. Specifically, the thickness of the hard coating layer may be 5 µm to 15 µm, preferably 5 µm to 10 µm, more preferably 6 µm to 9 µm. When the thickness exceeds 15 μm, there is a problem that the optical properties of the hard coating layer are deteriorated, and when the thickness of the hard coating layer is less than 5 μm, the protective function is deteriorated and durability at high temperature or high humidity is lowered.

The hard coating layer is excellent in the protective effect of the polarizer under high temperature or high humidity conditions. The hard coating layer is provided directly on the polarizer. To be provided directly on the polarizer means that the polarizer and the hard coating layer physically contact each other without intervening an adhesive layer. That is, the hard coating layer according to the exemplary embodiment of the present specification is formed directly on the polarizer without a separate adhesive layer, thereby providing a thin polarizing plate. In addition, since the hard coating layer of the polarizing plate according to the exemplary embodiment of the present specification can effectively suppress contraction or expansion of the polarizer at a high temperature without a separate protective film, tearing of the polarizer and the polarizing plate can be prevented.

Specifically, it can be confirmed through a high-grade crack growth test of the polarizer that effectively suppresses the contraction or expansion of the polarizer at a high temperature. As a result of the high-temperature crack growth test, the polarizer may have a ratio of the number of cracks (C2) leaking light to the total number of cracks (C1) of 20% or less, preferably 10% or less, and more preferably 5% or less. The high-temperature crack growth test method is a method of inducing an artificial crack in a polarizer and then leaving it at a high temperature to observe whether the crack grows. The standing condition may be a temperature condition of 80°C and a standing time condition of 100 hours to 300 hours. At this time, by calculating the number of cracks (C2) that leaks light compared to the number of cracks (C1) in the initial period, the incidence rate of cracks in the polarizing plate is derived.

The polarizing plate of the present invention has a structure that does not further include a protective film on the other surface of the surface facing the polarizer of the hard coating layer. As described above, the hard coating layer is excellent in high temperature, high humidity durability, and thus can effectively protect the polarizer even in a thin thickness. Therefore, even if a separate protective film is not provided, the polarizer can be effectively protected. The structure of the above polarizing plate is shown in FIGS. 1 to 3.

1 illustrates a polarizing plate according to an exemplary embodiment of the present specification. 1 illustrates a structure of a polarizing plate in which a hard coating layer 20 is provided on one surface of the polarizer 10.

2 shows a polarizing plate according to another exemplary embodiment of the present specification. 2, a hard coating layer 20 is provided on one surface of the polarizer 10, an adhesive layer 30 is provided on the other surface of the surface where the hard coating layer of the polarizer contacts, and a protective film 40 on the adhesive layer The structure of this equipped polarizing plate is illustrated.

In addition, Figure 3 shows a polarizing plate according to another embodiment of the present specification. 3 illustrates the structure of a polarizing plate provided with a hard coating layer 20 on both sides of the polarizer 10. As shown in FIG. 3, when a hard coating layer is provided on both sides of the polarizer, there is an advantage of being able to form a thin film with almost no retardation.

The hard coating layer may be formed by coating and curing a photocurable composition for a polarizing plate hard coating layer on one or both sides of a polarizer.

Meanwhile, the coating method is not particularly limited, and may be formed by a method well known in the art. For example, by applying the photocurable composition for a hard coating layer of the polarizing plate to one or both sides of a polarizer by a coating method well known in the art, such as spin coating, bar coating, roll coating, gravure coating, blade coating, etc. After forming the hard coating layer, it may be formed by a method of irradiating ultraviolet rays, which is irradiation light, using an ultraviolet irradiation device.

The wavelength of the ultraviolet rays is preferably 100 nm to 400 nm, more preferably 320 nm to 400 nm. Further, the irradiation light amount is more preferably 100mJ / cm ² to 1000mJ / cm ² are preferred, and 500mJ / cm ² to 1000mJ / cm ^2.

The irradiation time of the irradiation light is preferably 1 second to 10 minutes, more preferably 2 seconds to 30 seconds. When the irradiation time range is satisfied, there is an advantage of preventing excessive heat transfer from the light source, thereby minimizing the occurrence of running wrinkles in the polarizer.

The photocurable composition for the polarizing plate hard coating layer may be a non-(meth)acrylate system that does not substantially contain a (meth)acrylate compound. When the composition further includes a (meth)acrylate compound in the epoxy-based compound, if the polarizing plate including the adhesive layer formed from the composition for the adhesive layer is left at high temperature or high temperature and humidity for a long period of time, there is a problem that the amount of color difference change in the relational formula is large. I can.

The fact that the photocurable composition for the polarizing plate hard coating layer does not contain a (meth)acrylate compound substantially means that the photocurable composition for the polarizing plate hard coating layer does not contain a (meth)acrylate compound or a (meth)acrylate compound It means all cases containing a small amount. When the (meth)acrylate compound is not included in the composition, curing may be performed by a cationic photoinitiator. On the other hand, even when a small amount of the (meth)acrylate compound is included, curing may be performed by a cationic photoinitiator. Specifically, since some radicals may be generated by the cationic photoinitiator, the radical curable compound (meth)acrylate compound may also undergo curing.

The photocurable composition for the polarizing plate hard coating layer may be a cationic photocurable composition. That is, the hard coating layer may include a cured product of a cationic photocurable composition.

The hard coating layer may include a cured product of a photocurable composition including an epoxy compound and an oxetane compound. That is, the photocurable composition may include an epoxy compound and an oxetane compound.

The epoxy compound is for lowering the coefficient of thermal expansion after curing of the composition, and includes an alicyclic epoxy compound, an aliphatic epoxy compound, an aromatic epoxy compound, a hydrogenated epoxy compound, or an epoxy group-containing (meth)acrylic compound. These may be used alone or in combination of two or more.

The alicyclic epoxy compound includes one or more alicyclic epoxy rings, and refers to a compound in which the epoxy group is formed between two adjacent carbon atoms constituting the aliphatic ring. For example, dicyclopentadiene dioxide, limonene dioxide, 4-vinylcyclohexene dioxide, 2,4-epoxycyclohexylmethyl, 3,4-epoxycyclohexanecarboxylate, dicyclopentadiene dioxide, bis(3, 4-epoxycyclohexylmethyl) adipate, and the like, but are not limited thereto. In addition, 3,4-epoxycyclohexylmethyl-3,4'-epoxycyclohexanecarboxylate is preferable to lower the coefficient of thermal expansion after curing of the composition and to impart the hardness of the adhesive layer formed from the composition. Do.

Examples of the aliphatic epoxy compound include novolac epoxy, bisphenol A epoxy, bisphenol F epoxy, 1,4-cyclohexanedimethanol diglycidyl ether, 1,4-butanedioldiglycidyl ether, 1,6-hexane Diol diglycidyl ether, neopentyl diglycidyl ether, resorcinol diglycidyl ether, diethylene glycol diglycidyl ether, ethylene glycol diglycidyl ether, trimethylolpropane triglycidyl ether, n -Butyl glycidyl ether, 2-ethylhexyl glycidyl ether, etc. are mentioned.

The aromatic epoxy compound means an epoxy compound containing at least one aromatic hydrocarbon ring in the molecule, but is not limited thereto, for example, diglycidyl ether of bisphenol A, 4,4'-methylenediphenol digly Bisphenol-type epoxy resins such as cidyl ether, diglycidyl ether of bisphenol F, and diglycidyl ether of bisphenol S; Novolac-type epoxy resins such as phenol novolac epoxy resin, cresol novolac epoxy resin, and hydroxybenzaldehyde phenol novolac epoxy resin; And polyfunctional epoxy resins such as glycidyl ether of tetrahydroxyphenyl methane, glycidyl ether of tetrahydroxybenzophenone, and epoxidized polyvinylphenol.

The hydrogenated epoxy compound refers to an epoxy compound obtained by selectively hydrogenating the aromatic epoxy compound under pressure in the presence of a catalyst, and is not limited thereto, but among others, hydrogenated diglycidyl ether of bisphenol A It is preferable to use.

The epoxy group-containing (meth)acrylic compound refers to a compound including both an epoxy group and a (meth)acryloyloxy group in a molecule, and is not limited thereto, for example, glycidyl acrylate, 2-methylglyci Dyl acrylate, 3,4-epoxybutyl acrylate, 6,7-epoxyheptyl acrylate, 3,4-epoxycyclohexyl acrylate, glycidyl methacrylate, 2-methylglycidyl methacrylate, 3 , 4-epoxybutyl methacrylate, 6,7-epoxyheptyl methacrylate, 3,4-epoxycyclohexyl methacrylate, 4-hydroxybutyl acrylate glycidyl ether, and the like.

The epoxy compound may be an epoxy compound containing at least one alicyclic epoxy group.

The epoxy compound including one or more alicyclic epoxy groups may have two or more epoxy groups in the molecule, and at least one of the epoxy groups may be an alicyclic epoxy group. The epoxy compound including at least one alicyclic epoxy group may improve adhesion strength to other members of the composition. In addition, the glass transition temperature of the composition is increased to ensure sufficient durability of the adhesive layer, so that the occurrence of cracks in the polarizer can be prevented even under heat resistance or thermal shock conditions.

The epoxy compound including at least one alicyclic epoxy group may be one that does not substantially have an aromatic ring. In this case, photocuring efficiency may be improved, and optical properties after curing such as weather resistance and refractive index may be improved.

The epoxy compound including one or more alicyclic epoxy groups may have two or more epoxy groups in the molecule, and all of the epoxy groups may be alicyclic epoxy groups. In this case, the adhesive strength of the adhesive composition to other members can be further improved.

The number of carbon atoms of the alicyclic ring of the epoxy compound containing at least one alicyclic epoxy group may be 4 to 10, preferably 6.

The alicyclic ring of the epoxy compound containing at least one alicyclic epoxy group may be substituted or unsubstituted, and examples of the substituent include an alkyl group having 1 to 20 carbon atoms. In the carbon number range, the curing speed and the adhesive strength after curing may be improved. The alkyl group, unless otherwise specified, may mean a straight, branched or cyclic alkyl group having 1 to 20 carbon atoms, 1 to 16 carbon atoms, 1 to 12 carbon atoms, 1 to 8 carbon atoms, or 1 to 4 carbon atoms, and , The alkyl group may be optionally substituted by one or more substituents, or may be unsubstituted.

The epoxy compound containing at least one alicyclic epoxy group includes at least one alicyclic epoxy ring, and refers to a compound in which the epoxy group is formed between two adjacent carbon atoms constituting an aliphatic ring, and an alicyclic epoxy compound It may be named as, and may be a compound having at least one epoxy group bonded to an alicyclic ring in the molecule as represented by the following formula a1.

[Formula a1]

In Formula a1, m is an integer of 2 to 5, and the group _{obtained by removing one or more hydrogen atoms in (CH 2} )m in Formula a1 is a compound bonded to another chemical structure without an aromatic ring is an alicyclic epoxy compound. I can. That is, it may mean a compound containing one or more epoxidized aliphatic cyclic groups.

Examples of the epoxy compound including at least one alicyclic epoxy group may be represented by the following formula, but is not limited thereto.

As the epoxy compound including at least one alicyclic epoxy group, an epoxycyclohexylmethyl epoxycyclohexanecarboxylate-based compound represented by the following Formula 1 may be exemplified.

[Formula 1]

In Formula 1, R ₁ and R ₂ each independently represent hydrogen or an alkyl group.

As another example of the epoxy compound containing at least one alicyclic epoxy group, an epoxycyclohexane carboxylate-based compound of an alkanediol represented by the following formula (2) may be mentioned.

[Formula 2]

In Formula 2, R ₃ and R ₄ each independently represent hydrogen or an alkyl group, and n represents an integer of 2 to 20.

As another example of the epoxy compound containing at least one alicyclic epoxy group, an epoxy cyclohexylmethyl ester-based compound of dicarboxylic acid represented by the following formula (3) may be mentioned.

[Formula 3]

In Formula 3, R ₅ and R ₆ each independently represent hydrogen or an alkyl group, and p represents an integer of 2 to 20.

As another example of the epoxy compound containing at least one alicyclic epoxy group, an epoxycyclohexylmethyl ether compound of polyethylene glycol represented by the following formula (4) may be mentioned.

[Formula 4]

In Formula 4, R ₇ and R ₈ each independently represent hydrogen or an alkyl group, and q represents an integer of 2 to 20.

As another example of the epoxy compound containing at least one alicyclic epoxy group, an epoxycyclohexylmethyl ether compound of an alkanediol represented by the following formula (5) may be mentioned.

[Formula 5]

In Formula 5, R ₉ and R ₁₀ each independently represent hydrogen or an alkyl group, and r represents an integer of 2 to 20.

As another example of the epoxy compound containing at least one alicyclic epoxy group, a diepoxy citris pyro compound represented by the following formula (6) may be mentioned.

[Formula 6]

In Formula 6, R ₁₁ and R ₁₂ each independently represent hydrogen or an alkyl group.

As another example of the epoxy compound containing at least one alicyclic epoxy group, a diepoxy monospiro-based compound represented by the following formula (7) may be mentioned.

[Formula 7]

In Formula 7, R ₁₃ and R ₁₄ each independently represent hydrogen or an alkyl group.

As another example of the epoxy compound containing at least one alicyclic epoxy group, a vinylcyclohexene diepoxide compound represented by the following formula (8) may be mentioned.

[Formula 8]

In Formula 8, R ₁₅ represents hydrogen or an alkyl group.

As another example of the epoxy compound containing at least one alicyclic epoxy group, an epoxycyclopentyl ether compound represented by the following formula (9) may be mentioned.

[Formula 9]

In Formula 9, R ₁₆ and R ₁₇ each independently represent hydrogen or an alkyl group.

As another example of the epoxy compound containing at least one alicyclic epoxy group, a diepoxy tricyclodecane compound represented by the following formula (10) may be mentioned.

[Formula 10]

In Formula 10, R ₁₈ represents hydrogen or an alkyl group.

As another example of the epoxy compound containing at least one alicyclic epoxy group, more specifically, an epoxycyclohexylmethyl epoxycyclohexane carboxylate compound, an epoxycyclohexane carboxylate compound of an alkanediol, an epoxycyclohexylmethyl ester compound of a dicarboxylic acid Or it is preferable to use an epoxycyclohexylmethyl ether compound of an alkanediol, and 7-oxabicyclo[4,1,0]heptane-3-carboxylic acid and (7-oxa-bicyclo[4,1,0]hepto -3-yl) esterified product with methanol (a compound in which R ₁ and R ₂ are hydrogen in Formula 1); Ester of 4-methyl-7-oxabicyclo[4,1,0]heptane-3-carboxylic acid with (4-methyl-7-oxa-bicyclo[4,1,0]hepto-3-yl)methanol Cargo (in Formula 1, R ₁ is 4-CH ₃ , R ₂ is a compound of 4-CH ₃ ); Esterified product of 7-oxabicyclo[4,1,0]heptane-3-carboxylic acid and 1,2-ethanediol (a compound in which R ₃ and R ₄ are hydrogen and n is 2 in Formula 2); (7-oxabicyclo[4,1,0]hepto-3-yl) an esterified product of methanol and adipic acid (a compound in which R ₅ and R ₆ are hydrogen and p is 2 in Chemical Formula 3); (4-methyl-7-oxabicyclo[4,1,0]hepto-3-yl)methanol and adipic acid esterified product (R ₅ and R ₆ in Formula 3 are 4-CH ₃ and p is 2 phosphorus compound); And an ether product of (7-oxabicyclo[4,1,0]hepto-3-yl)methanol and 1,2-ethanediol (in Formula 5, R ₉ and R ₁₀ are hydrogen and r is 2 ) One or more selected from the group consisting of may be preferably used, but is not limited thereto.

The epoxy compound containing at least one alicyclic epoxy group is for increasing the glass transition temperature (Tg) of the composition and imparting the hardness of the adhesive layer formed from the composition, 3,4-epoxycyclohexylmethyl- 3,4'-epoxycyclohexanecarboxylate is preferred.

The oxetane compound is not particularly limited as long as it has at least one oxetanyl group in the molecule, and various oxetane compounds well known in the art may be used. For example, as the oxetane compound of the present invention, 3-ethyl-3-[(3-ethyloxetan-3-yl)methoxymethyl]oxetane, 1,4-bis[(3-ethyloxy) Cetan-3-yl)methoxymethyl]benzene, 1,4-bis[(3-ethyloxetan-3-yl)methoxy]benzene, 1,3-bis[(3-ethyloxetan-3-yl) ) Methoxy] benzene, 1,2-bis [(3-ethyl oxetan-3-yl) methoxy] benzene, 4,4'-bis [(3-ethyloxetan-3-yl) methoxy] ratio Phenyl, 2,2'-bis[(3-ethyloxetan-3-yl)methoxy]biphenyl, 3,3',5,5'-tetramethyl-4,4'-bis[(3-ethyl Oxetan-3-yl)methoxy]biphenyl, 2,7-bis[(3-ethyloxetan-3-yl)methoxy]naphthalene, bis[4-{(3-ethyloxetan-3-yl) )Methoxy}phenyl]methane, bis [2-{(3-ethyloxetan-3-yl)methoxy}phenyl]methane, 2,2-bis[4-{(3-ethyloxetan-3-yl) )Methoxy}phenyl]propane, a modified product of the etherification of a novolac-type phenol-formaldehyde resin with 3-chloromethyl-3-ethyloxetane, 3(4),8(9)-bis[(3-ethyl Oxetan-3-yl)methoxymethyl]-tricyclo[5.2.1.0 2,6]decane, 2,3-bis[(3-ethyloxetan-3-yl)methoxymethyl]norbornane, 1 ,1,1-tris[(3-ethyloxetan-3-yl)methoxymethyl]propane, 1-butoxy-2,2-bis[(3-ethyloxetan-3-yl)methoxymethyl] Butane, 1,2-bis[{2-(3-ethyloxetan-3-yl)methoxy}ethylthio]ethane, bis[{4-(3-ethyloxetan-3-yl)methylthio}phenyl ]Sulfide, 1,6-bis[(3-ethyloxetan-3-yl)methoxy]-2,2,3,3,4,4,5,5-octafluorohexane, etc. It is not limited.

The photocurable composition may further include a photoinitiator, a photosensitizer, or a photosensitizer.

The photoinitiator may be an iodine-based compound that absorbs a wavelength of 310 nm or less. Specifically, the photoinitiator refers to an iodine-based compound that is activated by absorbing a wavelength of 310 nm or less to produce a cation or Lewis acid by irradiation of active energy. For example, diphenyliodonium hexafluorophosphate (Iod-PF ₆ ), diphenyliodonium triflate (Iod-OSO ₂ CF ₃ ), diphenyliodonium p-toluenesulfonate (Iod-OSO ₂ PhCH ₃ ), diphenyliodonium chloride (Iod-Cl), [4-methylphenyl-(4-(2-methylpropyl)phenyl)]iodonium hexafluorophosphate (Irgacure 250), and the like, [4- Methylphenyl-(4-(2-methylpropyl)phenyl)]iodonium hexafluorophosphate (Irgacure 250) is preferred, but is not limited thereto.

The content of the photoinitiator is preferably 2 to 5 parts by weight, and more preferably 2.5 to 3.5 parts by weight, based on 100 parts by weight of the total photocurable composition. When the photoinitiator is included in an amount within the above numerical range, ultraviolet rays can effectively reach the inside of the hard coating layer, the polymerization rate is excellent, and the molecular weight of the resulting polymer can be prevented from decreasing. Therefore, there is an advantage of excellent cohesion and adhesion to the polarizer of the hard coating layer to be formed.

The photocurable composition includes a photosensitizer. The photosensitizer may be a thioxanthone-based photosensitizer.

The thioxanthone-based photosensitizer may be an alkyl thioxanthone-based, alkoxy thioxanthone-based, or halo thioxanthone-based photosensitizer. The specific structure is shown in Formula B below.

[Formula B]

In Formula B, R ₁ ′ to R ₈ ′ are the same or different, and each independently hydrogen; Halogen group; A substituted or unsubstituted alkyl group; Or it may be a substituted or unsubstituted alkoxy group.

In Formula B, R ₁ ′ to R ₈ ′ are the same or different, and each independently hydrogen; Halogen group; A substituted or unsubstituted C 1 to C 8 alkyl group; Or it may be a substituted or unsubstituted C 1 to C 8 alkoxy group.

More specific examples of the thioxanthone-based photosensitizer include 2-isopropyl thioxanthone, 4-isopropyl thioxanthone, 2,4-diethyl thioxanthone, 2,4-dichloro thioxanthone, 1 -Chloro-4-propoxythioxanthone, etc. are mentioned.

The content of the photosensitizer may be 0.01 to 0.4 parts by weight based on the total 100 parts by weight of the photocurable composition, preferably 0.1 to 0.3 parts by weight. When the photosensitizer is included in the above numerical range, the photoinitiator of 310 nm or less can be efficiently initiated by receiving ultraviolet rays of 380 nm or more, and the resulting polymer is effectively cured to the inside of the hard coating layer, resulting in excellent polymerization rate, and the resulting polymer The molecular weight of can be prevented from decreasing.

The photocurable composition further includes a photosensitization aid. Specifically, the photosensitization aid may be a naphthalene-based compound.

The photosensitizing aid may be a compound represented by the following formula (C).

[Formula C]

In Formula C,

R ₁₁ ′ and R ₁₂ ′ are the same as or different from each other, and each independently represent an alkyl group having 1 to 6 carbon atoms.

Types of the photosensitizing aid include 1,4-dimethoxy naphthalene, 1-ethoxy-4-methoxy naphthalene, 1,4-diethoxy naphthalene, 1,4-dipropoxy naphthalene, and 1,4-dibutoxy And naphthalene.

The content of the photosensitizing aid is preferably 1 to 3 parts by weight, and more preferably 1 to 2 parts by weight, based on 100 parts by weight of the total of the cationic photocurable composition. When the photosensitizer is included in an amount within the above numerical range, the photosensitizer is excited to help initiate the photoinitiator. Specifically, the anthracene-based photosensitizer excited by receiving ultraviolet rays of 380 nm or more immediately transfers energy to the photosensitizing aid, and the excited photosensitizing aid transfers energy so that the photoinitiator can be efficiently initiated. Accordingly, it is possible to effectively reach the inside of the hard coating layer, the polymerization rate is also excellent, and the molecular weight of the resulting polymer can be prevented from decreasing. Therefore, there is an advantage of excellent cohesion and adhesion to the polarizer of the hard coating layer to be formed.

The cationic photocurable composition may further include at least one of dyes, pigments, ultraviolet stabilizers, antioxidants, toning agents, reinforcing agents, fillers, antifoaming agents, surfactants, and plasticizers, if necessary.

The cationic photocurable composition preferably has a glass transition temperature of 90° C. or more and 130° C. or less after curing, and may be 100° C. to 130° C. When the glass transition temperature is in the numerical range as described above, it is possible to implement a hard coating layer having excellent durability even under a high temperature environment.

In the present specification, the glass transition temperature is applied to a release film (for example, a polyethylene terephthalate film) with a thickness of 50 µm, and after curing by irradiating ultraviolet rays under conditions of a light ^{amount of 1000 mJ/cm 2 or more, the release film is removed,} After laser cutting the specimen to a certain size, it is measured through dynamic mechanical analysis (DMA). At this time, the measurement temperature is increased from the starting temperature of -10°C to 160°C at a heating rate of 5°C/min, and the glass transition temperature is checked through the inflection of the storage modulus at the time of constant tensioning with 10% strain.

The viscosity at 25° C. of the cationic photocurable composition is preferably 50 cps or more and 200 cps or less, and more preferably 50 cps or more and 130 cps. When the viscosity of the photocurable composition for the hard coating layer of the polarizing plate satisfies the above numerical range, the thickness of the hard coating layer can be formed to be thin, and there is an advantage of excellent workability. The viscosity can be measured at room temperature using a No. 18 spindle using a Brookfield viscometer. At this time, the amount of the composition is appropriately 6.5 to 10 mL, and the stabilized value is measured within 5 minutes to avoid prolonged exposure to light.

The storage modulus of the hard coating layer at 80° C. is preferably 1,500 Mpa to 10,000 Mpa, more preferably 1,800 Mpa to 5,000 Mpa, and most preferably 2,000 Mpa to 3,500 Mpa.

When the storage modulus of the hard coating layer satisfies the above numerical range, there is an effect of effectively suppressing the stress applied to the polarizer, thereby effectively suppressing the occurrence of cracks in the polarizer due to contraction or expansion of the polarizer in a high temperature or high humidity environment. . In addition, it is possible to improve the adhesion to the polarizer. Therefore, by suppressing the shrinkage and expansion of the polarizing plate at high temperature, when the polarizing plate is applied to a liquid crystal panel or the like, it is possible to prevent the occurrence of light leakage as well as excellent adhesion.

The polarizer may be a polarizer well known in the art, for example, a film made of polyvinyl alcohol (PVA) containing iodine or a dichroic dye. The polarizer may be manufactured by dyeing iodine or a dichroic dye to a polyvinyl alcohol-based film, but a method of manufacturing the polarizer is not particularly limited. In the present specification, the polarizer refers to a state that does not include a hard coating layer (or protective film), and the polarizing plate refers to a state including a polarizer and a hard coating layer (or protective film).

Polarizing plate is a process of uniaxially stretching a polyvinyl alcohol-based resin film, a process of dyeing a polyvinyl alcohol-based resin film with a dichroic dye and adsorbing the dichroic dye, and a polyvinyl alcohol-based resin film adsorbed with a dichroic dye. It is produced through a step of treating with an aqueous boric acid solution, a step of washing with water after treatment with an aqueous boric acid solution, and bonding a hard coat layer to a uniaxially stretched polyvinyl alcohol-based resin film in which a dichroic dye is adsorbed and oriented.

Uniaxial stretching may be performed before dyeing with a dichroic dye, simultaneously with dyeing with a dichroic dye, or after dyeing with a dichroic dye. When uniaxial stretching is performed after dyeing with a dichroic dye, this uniaxial stretching may be performed before boric acid treatment or during boric acid treatment. In addition, it is also possible to uniaxially stretch in a plurality of these steps. In order to perform uniaxial stretching, it may be uniaxially stretched between rolls having different circumferential speeds or uniaxially stretched using a heat roll. Further, it may be dry stretching performed in the air, or wet stretching performed in a state swollen with a solvent. The draw ratio is not particularly limited, but is usually 4 to 8 times.

Meanwhile, the polarizer preferably has a thickness of 5 μm to 40 μm, and more preferably 5 μm to 25 μm. If the thickness of the polarizer is thinner than the above numerical range, optical properties may deteriorate, and if the thickness of the polarizer is thicker than the above numerical range, the amount of shrinkage of the polarizer at a low temperature (for example, -30°C) increases, thereby reducing the overall durability of the polarizing plate in relation to heat. .

In addition, when the polarizer is a polyvinyl alcohol-based film, the polyvinyl alcohol-based film may be used without particular limitation as long as it includes a polyvinyl alcohol resin or a derivative thereof. In this case, the derivatives of the polyvinyl alcohol resin include polyvinyl formal resin and polyvinyl acetal resin, but are not limited thereto. In addition, commercially available polyvinyl alcohol-based films such as P30, PE30, PE60 from Guraray, M2000, M3000, M6000, etc. from Japan Synthetic Company may be used, but the present invention is not limited thereto.

The polyvinyl alcohol-based film preferably has a degree of polymerization of 1,000 to 10,000, and more preferably 1,500 to 5,000. When the degree of polymerization satisfies the above numerical range, the movement of molecules is free and can be flexibly mixed with iodine or a dichroic dye.

The present specification provides a polarizing plate in which a protective film is attached to the other surface of the surface on which the hard coating layer of the polarizer is provided through an adhesive layer. That is, the polarizing plate of the present specification is a polarizer; A hard coating layer provided on one surface of the polarizer; And a protective film attached to the other surface of the polarizer through an adhesive layer.

Specifically, when the hard coating layer is formed on one surface of the polarizer, a separate transparent protective film may be attached to the polarizing plate through an adhesive layer to support and protect the polarizer on the opposite surface of the surface on which the hard coating layer is formed.

At this time, the protective film is to support and protect the polarizer, and protective films of various materials generally known in the art, for example, polyethylene terephthalate (PET) film, cycloolefin polymer (COP) , cycloolefin polymer) film, an acrylic film such as a triacetyl cellulose film (TAC, Tri-Acetyl Cellulose), etc. may be used. Among these, it is particularly preferable to use a polyethylene terephthalate film in consideration of optical properties, durability, economy, and the like.

On the other hand, the attachment of the polarizer and the protective film is performed by coating the adhesive composition on the surface of the polarizer or the protective film using a roll coater, gravure coater, bar coater, knife coater or capillary coater, and then heating them with a paper roll to laminate. Or, it may be performed by a method of laminating by pressing at room temperature or a method of irradiating UV after lamination.

The adhesive layer is a cured product of an adhesive composition, and the adhesive composition includes an epoxy compound and an oxetane compound. The description of the epoxy compound and the oxetane compound is as described above.

It is preferable that the adhesive layer is formed of a photocurable adhesive composition. As described above, when the adhesive layer is a curable resin layer formed of a photocurable composition, there is an advantage in that the manufacturing method is simple, and further, adhesion to the protective film is excellent. In addition, the durability of the polarizing plate can be further improved.

If necessary, the adhesive composition may further include a silane coupling agent. When a silane coupling agent is included, an effect of improving adhesive wetting may be obtained by lowering the surface energy of the adhesive. In this case, it is more preferable that the silane coupling agent includes a cationic polymerizable functional group such as an epoxy group, a vinyl group, and a radical group. In addition, in the case of using a silane coupling agent that does not contain a cationic polymerizable functional group, the effect of improving the wettability without lowering the glass transition temperature compared to a surfactant or a silane coupling agent that does not contain a cationic polymerizable functional group. There is. This is because the cationic polymerization functional group of the silane coupling agent reacts with the silane group of the adhesive composition to form a crosslinking form, thereby reducing the phenomenon that the glass transition temperature of the adhesive layer is lowered after curing.

Meanwhile, the adhesive layer may be formed by a method well known in the art. For example, it may be carried out by applying an adhesive composition to one side of a polarizer or a protective film to form an adhesive layer, and then laminating the polarizer and the protective film, and then curing. In this case, the coating may be performed by coating methods well known in the art, for example, spin coating, bar coating, roll coating, gravure coating, and blade coating. In addition, after coating the adhesive composition, a separate drying process may be further performed before curing. The drying method is not limited as long as it is a commonly used method.

The present specification provides an image display device including the polarizing plate described above. The image display device may be a liquid crystal display device (LCD), a plasma display device (PDP), and an organic light emitting display device (OLED).

More specifically, the image display device may be a liquid crystal display device including a liquid crystal panel and polarizing plates respectively provided on both sides of the liquid crystal panel, and in this case, at least one of the polarizing plates may be the aforementioned polarizing plate. That is, the polarizing plate is a polarizing plate including a polyvinyl alcohol-based polarizer dyed with iodine and/or a dichroic dye and a protective film provided on at least one surface of the polyvinyl alcohol-based polarizer. It is characterized in that it has a polarization canceling region having a single transmittance of 80% or more, an arithmetic mean roughness (Ra) of 200 nm or less, a polarization degree of 10% or less, and a sagging of 10 μm or less.

In this case, the type of the liquid crystal panel included in the liquid crystal display device is not particularly limited. For example, a panel of a passive matrix system such as a twisted nematic (TN) type, a super twisted nematic (STN) type, a ferroelectic (F) type, or a polymer dispersed (PD) type; An active matrix type panel such as a two terminal type or a three terminal type; There are a horizontal electric field (IPS; In Plane Switching) panel and a vertical alignment (VA; Vertical Alignment) panel, but are not limited thereto. Further, other components constituting the liquid crystal display device, for example, the types of upper and lower substrates (for example, color filter substrates or array substrates) are not particularly limited.

Hereinafter, examples will be described in detail in order to describe the present specification in detail. However, the embodiments according to the present specification may be modified in various forms, and the scope of the present specification is not construed as being limited to the embodiments described below. The embodiments of the present specification are provided to more completely describe the present specification to those of ordinary skill in the art.

<Experimental Example>-Preparation of a composition for forming a hard coating layer of a polarizing plate

To prepare a composition for forming a hard coating layer of a polarizing plate having the composition of Table 1 below.

division Composition/content Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Example 3 Example 4 Example 5 Polarizer Composition of hard coating layer composition (A) 100 100 100 100 100 100 100 100 (B) 20 20 20 20 20 20 20 20 (C) 23 23 23 23 23 23 23 23 (D) 2.7% 2.7% 2.7% 2.7% 2.7% 2.7% 2.7% 2.7% (E) One% One% One% 0 0 One% 2% One% (F1) 0.1% 0.3% 0.5% One% 0 0 0 0 (F2) 0 0 0 0 One% 0 0 0.3% Hard coating layer thickness Unit (㎛) 6.5㎛ 6.5㎛ 6.5㎛ 6.5㎛ 6.5㎛ 6.5㎛ 6.5㎛ 6.5㎛ Property evaluation Experimental Example 1 Yellowness (Y1) 0.18 0.25 0.35 0.65 0.6 0.1 0.1 0.2 Yellowness/Thickness (㎛ ^-1 ) 0.028 0.038 0.054 0.1 0.092 0.015 0.015 0.031 Experimental Example 2 Crack incidence rate (%) 5% 0% 0% 0% 0% 40% 31% 20% Experimental Example 3 Polarizer adhesion 4B 5B 5B 5B 5B 0B 0B 5B

(F2): 안트라센계 광증감제(UVS-1331)

(A) 내지 (F)의 수치값은 각 성분의 중량비를 나타냄.
(A) 내지 (D)의 수치값은 (A) 성분 100 중량부에 대한 각 성분의 중량비를 의미함.
(D) 내지 (F2)의 수치값은 (A) 내지 (C)의 총 중량에 대한 각 성분의 중량비를 의미함.(A): First epoxy compound (3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate, brand name: CEL-2021P, manufactured by Daicel)
(B): Second epoxy compound (1,4-cyclohexanedimethanol diglycidyl ether, trade name: LD-204)
(C): Oxetane compound (3-ethyl-3-[(3-ethyloxetan-3-yl)methoxymethyl]oxetane, brand name: OXT-221, manufactured by Doagosei)
(D): photoinitiator (Irgacure 250, manufactured by BASF)
(E): photosensitization aid (ET2201)
(F1): Thioxanthone-based photosensitizer (DETX)

(F2): Anthracene-based photosensitizer (UVS-1331)

The numerical values of (A) to (F) represent the weight ratio of each component.
The numerical values of (A) to (D) refer to the weight ratio of each component to 100 parts by weight of the component (A).
The numerical values of (D) to (F2) refer to the weight ratio of each component to the total weight of (A) to (C).

<Experimental Example 1: Measurement of yellowness>

The yellowness of each hard coating layer was measured by preparing a hard coating layer specimen having the same configuration as the composition of the hard coating layer. At this time, as a yellowness measurement equipment, a light-beam spectrometer (V-7100, manufactured by JASCO) was used.

In addition, the thickness of the hard coating layer was measured using a FESEM SU-8020 SYSTEM equipment (measurement conditions: acceleration voltage 2 kV, emission current: 10uA, working distance: 8mm, Detector: SE).

<Experimental Example 2: High Temperature Crack Test>

The polarizer crack growth inhibition test by the hard coating layer was conducted. After inducing an artificial crack in the polarizer, a hard coating layer was formed on the polarizer using the compositions of Examples and Comparative Examples to prepare a polarizing plate. Then, it was left at a high temperature to observe whether or not cracks were grown. Specifically, the polarizer was scratched with a load of 100g to cause an artificial crack in the polarizer, and the rest of the manufacturing conditions were the same to prepare a polarizing plate.

The manufactured polarizing plate was cut into a width of 120 mm and a length of 100 mm, and then left at 80° C. for 100 to 300 hours or more, and then cracks were observed due to contraction of the polarizer and light leakage was observed, compared to the initial total number of cracks (C1). By calculating the number of cracks (C2) leaking light, the incidence rate of cracks in the polarizing plate was derived. Specifically, 200 initial cracks were generated, and the number of cracks leaking light among the initial cracks was calculated.

*Crack incidence rate: Number of cracks leaking light/number of initial total cracks x 100(%)

<Experimental Example 3: PVA adhesion test>

Using a cross cutter on the hard coating layer, place it on a cutting guide or a suitable ruler, and draw on the sample horizontally and vertically in a grid pattern at 1 mm intervals. After that, after washing the surface of the hard coating layer with a brush or a dust-free cloth, attach an Ichibang tape (Cellotape manufactured by Nichiban Co., Ltd.). Observe. According to the crosscut classification criteria (ASTM), the degree of adhesion is classified from 0B to 5B. In addition, it can be measured according to the measurement standard D3359-87.

<Experimental Example 4: Measurement of yellowness according to thickness>

While changing the thickness of the hard coating layer of the polarizing plate according to Example 2 and Comparative Example 2, the yellowness (Y1) of the hard coating layer according to the thickness was measured.

Yellowness (Y1) Hard coating layer thickness 5㎛ 6.5㎛ 8㎛ 10㎛ 13㎛ Example 2 0.16 0.18 0.21 0.22 0.3 Comparative Example 2 0.63 0.65 0.77 0.83 0.91

<Evaluation result>

In the case of using a thioxanthone-based photosensitizer (DETX) as a photosensitizer, it was confirmed that the heat resistance of the hard coating layer was superior compared to the case of using an anthracene-based photosensitizer (UVS-1331) (Experimental Example 2: Implementation Comparison of Example 2 and Example 5).

In addition, when the hard coating layer composition did not contain a photosensitizer, the yellowness did not increase (Experimental Example 1), but it was confirmed that the degree of curing was insignificant and the heat resistance of the hard coating layer was poor (Experimental Example 2: Example 3 and Example 4)

In the case of using a thioxanthone-based photosensitizer (DETX) as a photosensitizer, the degree of curing is excellent in the long wavelength region, so that the heat resistance of the hard coat layer is excellent (Experimental Example 2: Examples 1 and 2 and Comparative Examples 1 to 3). However, when excessive use of a thioxanthone-based photosensitizer (DETX) increases the yellowness of the hard coating layer (Comparative Examples 1 and 2), a thioxanthone-based photosensitizer (DETX) is used in a certain range. It was possible to prevent an increase in yellowness of the hard coating layer (Examples 1 and 2).

That is, in order to prevent the increase in yellowness while securing the heat resistance of the hard coating layer, it was confirmed that a thioxanthone-based photosensitizer (DETX) should be used in a specific range instead of the conventional anthracene-based photosensitizer.

10: polarizer
20: hard coating layer
30: adhesive layer
40: protective film

Claims (12)

Polarizer; And
Including a hard coating layer provided on at least one surface of the polarizer,
The polarizing plate that the hard coating layer satisfies the following relational expression.
[Relationship]
Yellowness of the hard coating layer (Y1) / the thickness of the hard coating layer ≤ 0.05 (㎛ ^-1 ) The method according to claim 1,
The polarizing plate that the yellowness (Y1) of the hard coating layer is 0.3 or less. The method according to claim 1,
The polarizing plate that the thickness of the hard coating layer is 5 ㎛ to 15 ㎛. The method according to claim 1,
As a result of the high-temperature crack growth test, the polarizer has a ratio of the number of cracks (C2) leaking light to the total number of cracks (C1) is 20% or less. The method according to claim 1,
The polarizing plate that does not further include a protective film on the other surface of the surface facing the polarizer of the hard coating layer. The method according to claim 1,
The hard coating layer is a polarizing plate comprising a cured product of a cationic photocurable composition. The method of claim 6,
The cationic photocurable composition is a polarizing plate comprising an epoxy compound and an oxetane compound. The method of claim 6,
The cationic photocurable composition is a polarizing plate comprising a thioxanthone-based photosensitizer. The method of claim 8,
The content of the thioxanthone-based photosensitizer is 0.01 to 0.4 parts by weight based on the total 100 parts by weight of the cationic photocurable composition polarizing plate. The method according to claim 1,
The hard coating layer is a polarizing plate provided directly on the polarizer. The method according to claim 1,
A polarizing plate in which a protective film is attached to the other surface of the surface provided with the hard coating layer of the polarizer through an adhesive layer. An image display device comprising the polarizing plate of any one of claims 1 to 11.

Images