KR102514153B1 - Polarizing plate and liquid crystal display apparatus comprising the same - Google Patents

Abstract

A polarizing plate including a polarizer, a first protective layer laminated on an upper surface of the polarizer, and a second protective layer laminated on a lower surface of the polarizer, wherein the polarizing plate has an orthogonal transmittance ratio represented by Equation 1 of 2 or more and 10 or less Phosphorus, a polarizing plate and a liquid crystal display device including the same are provided.

Description

A polarizing plate and a liquid crystal display device including the same {POLARIZING PLATE AND LIQUID CRYSTAL DISPLAY APPARATUS COMPRISING THE SAME}

The present invention relates to a polarizing plate and a liquid crystal display device including the same.

In an IPS (In Plane Switching) liquid crystal mode liquid crystal display device, the directionality of the liquid crystal is inclined in the Z-axis direction by a pre-tilt angle according to the rubbing direction of the liquid crystal. Also, in the liquid crystal display of the IPS liquid crystal mode, a phase-free film having no phase difference is mainly used. Therefore, light leakage inevitably occurs on both sides of the screen of the liquid crystal display device. An area seen as blue exists on one side and an area seen as yellow exists on the other side, and a visual difference between both sides may occur, thereby deteriorating screen quality. In particular, as the screen of the liquid crystal display device becomes larger, the visual difference between both sides and diagonals may become larger. On the other hand, as the polarizing plate is used in a liquid crystal display device, the degree of polarization must be excellent.

The background art of the present invention is disclosed in Korean Patent Publication No. 10-2016-0006817 and the like.

An object of the present invention is to provide a polarizer capable of reducing the visual difference between both sides in a black mode.

Another object of the present invention is to provide a polarizing plate having excellent polarization degree.

Another object of the present invention is to provide a polarizing plate capable of achieving the above object of the present invention in a simple and economical way and also obtaining a thinning effect.

One aspect of the present invention is a polarizing plate.

1. The polarizing plate includes a polarizer, a first protective layer laminated on an upper surface of the polarizer, and a second protective layer laminated on a lower surface of the polarizer, and the polarizing plate has an orthogonal transmittance ratio of 2 or more represented by Equation 1 below less than 10

[Equation 1]

Ratio of orthogonal transmittance = Tc(@480nm)/Tc(@660nm)

(In Equation 1, Tc(@660nm) is the orthogonal transmittance (unit: %) at a wavelength of 660nm of the polarizer,

Tc(@480nm) is orthogonal transmittance (unit: %) at a wavelength of 480nm of the polarizer.

In 2.1, the orthogonal transmittance ratio represented by Equation 1 may be 3 or more and 8 or less.

In 3.1-2, the polarizer may have orthogonal transmittance of 0.001% or more and 0.01% or less at a wavelength of 480 nm.

In 4.1-3, the polarizer may have orthogonal transmittance of 0.0005% or more and 0.01% or less at a wavelength of 660 nm.

In 5.1-4, the polarizing plate may have an orthogonal transmittance ratio of 1 or more and 20 or less represented by Equation 2 below:

[Equation 2]

Ratio of orthogonal transmittance = Tc(@700nm)/Tc(@660nm)

(In Equation 2 above,

Tc (@660nm) is the orthogonal transmittance (unit: %) at a wavelength of 660nm of the polarizer,

Tc (@700nm) is the orthogonal transmittance (unit: %) at a wavelength of 700nm of the polarizer.

In 6.1-5, the polarizer may have orthogonal transmittance of 0.001% or more and 0.02% or less at a wavelength of 700 nm.

In 7.1-6, the second protective layer may be laminated on the light incident surface of the polarizer.

In 8.1-7, the second protective layer may have a thickness direction retardation (Rth) of -60 nm to +10 nm at a wavelength of 550 nm.

In 9.1-8, the second protective layer may have an in-plane retardation (Re) of 0 nm to 10 nm at a wavelength of 550 nm.

In 10.1-9, the second protective layer may be formed of a composition for a cellulose ester-based coating layer.

In 11.10, the composition may include a cellulose ester-based compound including at least one of cellulose acetate (CA), cellulose acetate propionate (CAP), and cellulose acetate butyrate (CAB).

At 12.10, the composition may further include an additive having a fused ring.

In 13.12, the additive having the fused ring may have an aromatic group.

In 14.1-13, the first protective layer may have an in-plane retardation (Re) of 8,000 nm or more at a wavelength of 550 nm.

In 15.1-14, when the absorption axis of the polarizer is 0°, the angle between the slow axis of the first protective layer and the absorption axis of the polarizer may be -5° to +5°.

In 16.1-15, a third protective layer may be further laminated on the lower surface of the second protective layer.

In 17.16, the laminate of the second protective layer and the third protective layer may have a thickness direction retardation (Rth) of -50 nm to -10 nm at a wavelength of 550 nm.

In 18.16, the third passivation layer may have an in-plane retardation (Re) of 10 nm or less at a wavelength of 550 nm.

19.16, the third passivation layer may have a thickness direction retardation Rth different from that of the second passivation layer at a wavelength of 550 nm.

The liquid crystal display device of the present invention includes the polarizing plate of the present invention.

The present invention provides a polarizing plate capable of reducing the visual difference between both sides in a black mode.

The present invention provides a polarizing plate having excellent polarization degree.

The present invention provides a polarizing plate capable of achieving the above object of the present invention in a simple and economical way and also obtaining a thinning effect.

1 is a cross-sectional view of a polarizing plate according to an embodiment of the present invention.
2 is a cross-sectional view of a polarizing plate according to another embodiment of the present invention.
3 is a cross-sectional view of a polarizing plate according to another embodiment of the present invention.
Figure 4 shows the orthogonal transmittance (Tc, unit: %) according to the wavelength (unit: nm) of the polarizers of Examples and Comparative Examples.
Figure 5 shows the color coordinate results of the side in the black mode of Examples and Comparative Examples.

Hereinafter, with reference to the accompanying drawings, embodiments of the present application will be described in more detail. However, the technology disclosed in this application is not limited to the embodiments described herein and may be embodied in other forms. However, the embodiments introduced herein are provided so that the disclosed content can be thorough and complete and the spirit of the present application can be sufficiently conveyed to those skilled in the art. In the drawing, in order to clearly express the components of each device, the size of the components, such as width or thickness, is shown somewhat enlarged. In a plurality of drawings, like reference numerals denote substantially the same components.

In this specification, "upper" and "lower" are defined based on the drawings, and depending on the perspective, "upper" may be changed to "lower" and "lower" to "upper", and "on" or What is referred to as “on” may include not only immediately above but also the case of intervening other structures in the middle. On the other hand, what is referred to as "directly on" or "directly on" or "directly formed" indicates that no other structure such as an intermediate is intervened.

In this specification, "in-plane retardation (Re)" is represented by the following formula A, "thickness direction retardation (Rth)" is represented by the following formula B, and "degree of biaxiality (NZ)" is represented by the following formula C:

[Equation A]

Re = (nx - ny) x d

[Equation B]

Rth = ((nx + ny)/2 - nz) x d

[Equation C]

NZ = (nx - nz)/(nx - ny)

(In the above formulas A to C, nx, ny, nz are the refractive indices in the slow axis direction, the fast axis direction, and the thickness direction of the optical element at the measurement wavelength, respectively, and d is the thickness of the optical element (unit: nm)).

In the present specification, when describing a range, "X to Y" means "X or more and Y or less" (X≤ and ≤Y).

The inventor of the present invention is a polarizing plate used in an IPS liquid crystal mode liquid crystal display, and the polarization degree of the polarizing plate is increased by setting the ratio of the orthogonal transmittance at a wavelength of 480 nm of the polarizing plate to the orthogonal transmittance at a wavelength of 660 nm of the polarizing plate to be 2 or more and 10 or less. The present invention was completed after confirming that the difference in color and visual perception between the left screen and the right screen could be reduced when applied to an IPS liquid crystal mode liquid crystal display device while maintaining and/or increasing. In particular, the present invention can reduce the color difference and visual sensation difference between the left screen and the right screen from the side in a black mode in which voltage is not driven. The "side" may mean 30 ° to 60 ° or 120 ° to 150 ° when the front is 0 °, but is not limited thereto.

Hereinafter, a polarizing plate according to an embodiment of the present invention will be described with reference to FIG. 1 .

Referring to FIG. 1, the polarizing plate includes a polarizer 10, a first protective layer 20 laminated on the upper surface of the polarizer 10, and a second protective layer 20 sequentially laminated on the lower surface of the polarizer 10 from the polarizer 10. A protective layer 30 is included.

Although not shown in FIG. 1 , the first protective layer may be laminated on the light exit surface of the polarizer, and the second protective layer may be laminated on the light incident surface of the polarizer. However, the present invention is not limited thereto. Preferably, the first protective layer may be laminated on the light incident surface of the polarizer, and the second protective layer may be laminated on the light exit surface of the polarizer.

The polarizing plate has an orthogonal transmittance ratio of 2 or more and 10 or less, represented by Equation 1 below:

[Equation 1]

Ratio of orthogonal transmittance = Tc(@480nm)/Tc(@660nm)

(In Equation 1 above,

Tc (@660nm) is the orthogonal transmittance (unit: %) at a wavelength of 660nm of the polarizer,

Tc(@480nm) is orthogonal transmittance (unit: %) at a wavelength of 480nm of the polarizer.

The ratio of the orthogonal transmittance in Equation 1 means the ratio of the orthogonal transmittance at a wavelength of 480 nm of the polarizing plate to the orthogonal transmittance at a wavelength of 660 nm of the polarizing plate. When the orthogonal transmittance ratio of Equation 1 is 2 or more and 10 or less, color difference and visual perception difference between the left screen and the right screen can be reduced not only in the white mode but also in the black mode, and the polarization degree can be excellent. Through this, when the polarizer is applied to an IPS liquid crystal display device, the difference in color and visual perception between the left screen and the right screen can be reduced in black mode, and the polarization degree can be excellent, so the screen quality can be excellent.

Preferably, the ratio of orthogonal transmittances in Equation 1 may be 2 or more and 8 or less, and 2 or more and less than 8, more preferably 3 or more and 8 or less, 3 or more and less than 8, 3 or more and 6 or less, and 3 or more and 5 or less. It can be.

In the present invention, by limiting the ratio of the orthogonal transmittance of the polarizer, it is possible to reduce the color difference and the visual difference between the left screen and the right screen of the polarizer in the black mode. As the orthogonal transmittance at a wavelength of 480nm is increased, more blue-type light is emitted so that the difference in color and visual sensation between the left screen and the right screen can be reduced in black mode. can be lowered Accordingly, in the present invention, the orthogonal transmittance at a wavelength of 660 nm is increased while the orthogonal transmittance at a wavelength of 480 nm is increased, and the ratio between the orthogonal transmittances is specified to be 2 or more and 10 or less, thereby obtaining the above-described effects of the present invention.

In one embodiment, the polarizer may have an orthogonal transmittance of 0.001% or more and 0.01% or less, preferably 0.003% or more and 0.006% or less at a wavelength of 480 nm. Within this range, the orthogonal transmittance ratio of Equation 1 can be easily reached, it can be used as a polarizing plate, color difference and luminous difference can be reduced, and polarization degree can be excellent.

In one embodiment, the polarizer may have an orthogonal transmittance at a wavelength of 660 nm lower than that at a wavelength of 480 nm, and may be 0.0005% or more and 0.01% or less, preferably 0.001% or more and 0.005% or less. Within this range, the orthogonal transmittance ratio of Equation 1 can be easily reached.

In one embodiment, the polarizing plate may have a polarization degree of 99.9% or more, for example, 99.99% to 99.999%. Within the above range, it can be used as a polarizing plate in a liquid crystal display device.

The polarizing plate may have an orthogonal transmittance ratio of 1 or more and 20 or less, represented by Equation 2 below:

[Equation 2]

Ratio of orthogonal transmittance = Tc(@700nm)/Tc(@660nm)

(In Equation 2 above,

Tc (@660nm) is the orthogonal transmittance (unit: %) at a wavelength of 660nm of the polarizer,

Tc (@700nm) is the orthogonal transmittance (unit: %) at a wavelength of 700nm of the polarizer.

By blocking transmission of yellow-based light within the above range, the difference in visual perception and color between the left screen and the right screen can be further reduced.

Preferably, the orthogonal transmittance ratio in Equation 2 may be 1 or more and 15 or less, or 2 or more and 12 or less.

The polarizing plate of the present invention satisfies the orthogonal transmittance ratio of Equation 2 and at the same time satisfies the orthogonal transmittance ratio of Equation 1, thereby increasing the degree of polarization and reducing the visual difference and color difference between the left screen and the right screen.

In one embodiment, the polarizer may have an orthogonal transmittance of 0.001% or more and 0.02% or less, preferably 0.003% or more and 0.015% or less at a wavelength of 700 nm. Within this range, the orthogonal transmittance ratio of Equation 1 can be easily reached and can be used as a polarizing plate.

By including the second protective layer, the polarizing plate may satisfy the orthogonal transmittance ratio and polarization degree of Equation 1 in the polarizing plate in which the first protective layer, the polarizer, and the second protective layer are stacked.

The second protective layer is laminated on the light incident surface of the polarizer to emit polarized light incident from the lower surface of the second protective layer to the polarizer. The second protective layer is disposed on the lower surface of the polarizer to protect the polarizer.

The thickness direction retardation (Rth) of the second protective layer at a wavelength of 550 nm may be -60 nm to +10 nm. In the above range, the orthogonal transmittance ratio of Equation 1 may be reached, and the thinning effect of the polarizing plate may be obtained with the thin second protective layer. Preferably, the second protective layer may have an Rth of -40 nm to 0 nm, more preferably -40 nm to -10 nm, or -30 nm to -5 nm at a wavelength of 550 nm.

The second passivation layer may have a thickness direction retardation (Rth) of -80 nm to -0 nm at a wavelength of 480 nm. In the above range, the orthogonal transmittance ratio of Equation 1 may be reached, and the thinning effect of the polarizing plate may be obtained with the thin second protective layer. Preferably, the second protective layer may have an Rth of -50 nm to -0 nm, more preferably -40 nm to -10 nm at a wavelength of 480 nm.

The thickness direction retardation (Rth) of the second protective layer at a wavelength of 660 nm may be -60 nm to +10 nm. In the above range, the orthogonal transmittance ratio of Equation 1 may be reached, and the thinning effect of the polarizing plate may be obtained with the thin second protective layer. Preferably, the Rth of the second protective layer may be -30 nm to 0 nm, more preferably -25 nm to 0 nm at a wavelength of 660 nm.

In one embodiment, the ratio of Rth at a wavelength of 480 nm to Rth at a wavelength of 550 nm according to Equation 3 below is 0 or more and 8 or less, preferably 1 or more and 3 or less, and at a wavelength of 550 nm according to Equation 4 below The ratio of Rth at a wavelength of 660 nm to Rth of may be 0 or more and 6 or less, preferably 0 or more and 1 or less. Through this, the polarizer can satisfy the effect of reducing the lateral visual difference:

[Equation 3]

Rth(@480nm)/Rth(@550nm)

(In Equation 3 above,

Rth (@550nm) is the phase difference in the thickness direction of the second protective layer at a wavelength of 550nm (unit: nm),

Rth (@480nm) is the phase difference in the thickness direction of the second protective layer at a wavelength of 480nm (unit: nm)

[Equation 4]

Rth(@660nm)/Rth(@550nm)

(In Equation 4 above,

Rth (@550nm) is the phase difference in the thickness direction of the second protective layer at a wavelength of 550nm (unit: nm),

Rth(@660nm) is the phase difference in the thickness direction of the second passivation layer at a wavelength of 660nm (unit: nm).

The second passivation layer may have an in-plane retardation Re of 0 nm to 10 nm, for example, 0 nm to 5 nm at a wavelength of 550 nm.

By including the coating layer described in detail below, the second protective layer may achieve the effect of thinning the polarizer and the orthogonal transmittance ratio of Equation 1 above, and may reduce side visibility and color difference. In particular, as will be described in detail below, the coating layer can be formed by applying the composition for the coating layer described below to a substrate (eg, a polarizer, etc.) to form a coating film and drying, so that the ratio of the orthogonal transmittance of Equation 1 can be obtained in a simple and economical way. can be reached

When the second protective layer is a film prepared by stretching an unstretched resin film formed of a polymer, the orthogonal transmittance ratio of Equation 1 of the present invention cannot be reached.

The coating layer for the second protective layer is a coating layer containing a cellulose ester-based compound, and may be formed from a composition for a coating layer containing a cellulose ester-based compound.

The cellulose ester-based compound includes at least one of a cellulose ester-based resin, a cellulose ester-based oligomer, and a cellulose ester-based monomer. These may be included alone or in combination of two or more.

A cellulose ester-based compound refers to the condensation reaction product from the reaction of hydroxyl groups on cellulose with carboxylic acid groups of a carboxylic acid. Cellulose ester-based compounds may be regioselectively or randomly substituted. Regioselectivity can be measured by determining the relative degree of substitution at C6, C3 and C2 on the cellulose ester by carbon 13 NMR. Cellulose esters can be prepared by conventional methods by contacting a cellulose solution with one or more C1 to C20 acylating agents for a contact time sufficient to provide a cellulose ester having the desired degree of substitution and polymerization. Preferred acylating agents are one or more C1 to C20 straight or branched chain alkyl or aryl carboxylic acid anhydrides, carboxylic acid halides, diketones, or acetoacetic acid esters. Examples of anhydrides of carboxylic acids include acetic anhydride, propionic anhydride, butyric anhydride, isobutyric anhydride, valeric anhydride, hexanoic anhydride, 2-ethylhexanoic anhydride, nonanoic anhydride, lauric anhydride, palmitic anhydride, stearic anhydride, benzoic anhydride, substituted benzoic anhydride, phthalic anhydride, isophthalic anhydride. Examples of carboxylic acid halides include acetyl, propionyl, butyryl, hexanoyl, 2-ethylhexanoyl, lauroyl, palmitoyl, benzoyl, substituted benzoyl, and stearoyl chloride. Examples of acetoacetic acid esters may include methylacetoacetate, ethylacetoacetate, propylacetoacetate, butylacetoacetate, and tertiarybutylacetoacetate. Most preferred acylating agents are C2 to C9 straight chain or branched chain alkyl carboxylic acid anhydrides such as acetic anhydride, propionic anhydride, butyric anhydride, 2-ethylhexanoic anhydride, nonanoic anhydride, stearic anhydride and the like.

Preferable examples of the cellulose ester-based compound may include, but are not limited to, one or more of cellulose acetate (CA), cellulose acetate propionate (CAP), and cellulose acetate butyrate (CAB).

The composition for the coating layer further includes an additive having a fused ring in addition to the cellulose ester-based compound. The additive having the fused ring allows the thickness direction retardation (Rth) of the second protective layer to be better expressed. The additive having the fused ring may include naphthalene, anthracene, phenanthrene, pyrene, Structure 1 below, or Structure 2 below. The additive having the fused ring may include 2-naphthyl benzoate, 2,6-naphthalene dicarboxylic acid diester of Structure 3 below, naphthalene, abietic acid ester of Structure 4 below, etc., but is limited thereto doesn't work:

[Structure 1]

[Structure 2]

[Structure 3]

(In Structure 3, R is C1 to C20 alkyl or C6 to C20 aryl, n is an integer from 0 to 6)

[Structure 4]

(In Structure 4 above, R is C1 to C20 alkyl or C6 to C20 aryl)

Preferably, the additive having a fused ring is an additive having an aromatic ring, such as naphthalene, anthracene, phenanthrene, pyrene, 2-naphthyl benzoate, 2,6-naphthalene dicarboxylic acid diester of Structure 3 above. One or more of them may be included.

The additive having a fused ring may be included in an amount of 5 wt % to 90 wt %, preferably 10 wt % to 50 wt %, in the second protective layer. There may be an effect of reaching the orthogonal transmittance ratio of Equation 1 above by making the thickness direction retardation range described above better.

The second protective layer may further include additives such as a plasticizer, a stabilizer, a UV absorber, an antiblocking agent, a slip agent, a lubricant, a dye, a pigment, and a retardation improver, in addition to the above-mentioned additives having a fused ring.

In one embodiment, the second protective layer may be the above-described coating layer alone. In this case, the second protective layer may be directly formed on the polarizer. A laminate of the polarizer and the second protective layer may be prepared by coating and drying the composition for the coating layer for the second protective layer on one surface of the polarizer.

The second protective layer may have a thickness of 1 μm to 20 μm, preferably 1 μm to 10 μm, or 1 μm to 8 μm. Within the above range, there may be an effect of reducing the lateral visual difference.

The first protective layer is disposed to face the second protective layer with respect to the polarizer. The first protective layer is disposed on one surface of the polarizer to protect the polarizer and increase mechanical strength of the polarizer.

The first protective layer may include an optically transparent resin film. For example, the first protective layer may have a total light transmittance of 90% or more, for example, 95% or more at a wavelength of 550 nm. Within the above range, the total light transmittance of the polarizing plate may be increased and used for the polarizing plate.

Resins for the first protective layer include cellulose ester-based resins including triacetyl cellulose (TAC), cyclic polyolefin-based resins including amorphous cyclic polyolefin (COP), polycarbonate-based resins, and polyethylene terephthalate (PET). ), polybutylene terephthalate (PBT), polyethylene naphthalate, polyester-based resins including polybutylene naphthalate, polyethersulfone-based resins, polysulfone-based resins, polyamide-based resins, polyimide-based resins, A protective film formed of at least one of poly(meth)acrylate-based resins including cyclic-polyolefin-based resins and polymethyl methacrylate resins, polyvinyl alcohol-based resins, polyvinyl chloride-based resins, and polyvinylidene chloride-based resins. It may include, but is not limited thereto. Preferably, the first protective layer may be a polyester-based resin film including PET, PNT, and the like.

In one embodiment, the first protective layer is a stretched film, and the in-plane retardation Re at a wavelength of 550 nm may be 500 nm or less, for example, 100 nm to 300 nm. Within the above range, when the polarizer is applied, it is possible to improve screen quality under optimal conditions for improving the difference in lateral viewing angle.

In another embodiment, the first protective layer may be a stretched film and have an in-plane retardation Re of 8,000 nm or more at a wavelength of 550 nm, for example, 8,000 nm to 15,000 nm, 8,000 nm to 13,000 nm, or 8,000 nm to 12,000 nm. Within the above range, when the polarizer is applied, it is possible to improve screen quality under optimal conditions for improving the difference in lateral viewing angle.

In one embodiment, the first protective layer of the polarizing plate may have an in-plane retardation Re of 500 nm or less or 8,000 nm or more at a wavelength of 550 nm, and a ratio of orthogonal transmittance represented by Equation 1 to 2 or more and 10 or less. Through this, it has an effect of lowering the visual difference and the color difference between the left screen and the right screen.

The first protective layer may have a thickness direction retardation Rth of 15,000 nm or less at a wavelength of 550 nm, preferably 8,000 nm to 15,000 nm, or 8,000 nm to 13,000 nm. Within the above range, there may be an effect of reducing the difference in visual perception and color between the left screen and the right screen.

The first passivation layer may have a degree of biaxiality NZ of 1.8 or less, 15 or more, and preferably 1.0 to 1.8 or 15 to 20 at a wavelength of 550 nm. Within the above range, there may be an effect of reducing the difference in visual perception and color between the left screen and the right screen.

The first protective layer is a stretched film and has a slow axis and a fast axis. When the absorption axis (standard) of the polarizer is 0°, the angle between the slow axis of the first protective layer and the absorption axis of the polarizer is -5° to +5°, preferably -3° to +5°. It can be 3° or 0°. Within the above range, there may be an effect of reducing the visual difference between the left screen and the right screen. When displaying the angle, '-' indicates a counterclockwise direction with respect to the reference, and '+' indicates a clockwise direction with respect to the reference.

The first protective layer is a stretched film and may be a uniaxially stretched film or a biaxially stretched film. In one embodiment, the first protective layer may be a MD uniaxially stretched or TD uniaxially stretched film. In another embodiment, the first protective layer may be a MD and TD sequential or simultaneous biaxially oriented film. Preferably, the first protective layer is a TD uniaxially stretched film, and it is easy to secure the above-described in-plane retardation Re. Stretching may be performed by one or more methods of dry stretching or wet stretching. During dry stretching, the stretching temperature may be 20°C to 50°C, preferably 40°C to 50°C, and during wet stretching, the stretching temperature may be 20°C to 50°C, preferably 40°C to 50°C. The stretching ratio may be 2 to 7 times, preferably 3 to 6 times.

The first protective layer may have a thickness of 20 μm to 200 μm, preferably 40 μm to 100 μm. Within this range, it can be used for a polarizing plate.

Although not shown in FIG. 1, the first protective layer may be adhered to the polarizer by an adhesive layer. The adhesive layer may be formed of one or more of water-based adhesives and photocurable adhesives commonly known to those skilled in the art.

Although not shown in FIG. 1 , the first protective layer may provide an additional function to the polarizer by including a surface treatment layer on an upper surface, that is, a surface not in contact with the polarizer. The surface treatment layer may include at least one of a hard coating layer, an anti-reflection layer, an anti-fingerprint layer, a low-reflection layer, an anti-glare layer, a primer layer, and an ultra-low-reflection layer, but is not limited thereto.

The polarizer may include a polyvinyl alcohol-based polarizer prepared by uniaxially stretching a polyvinyl alcohol-based film, or a polyene-based polarizer prepared by dehydrating a polyvinyl alcohol-based film. The polarizer may have a thickness of 5 μm to 40 μm, preferably 5 μm to 30 μm. Within this range, it can be used for display devices.

Although not shown in FIG. 1 , an adhesive layer may be additionally included on the lower surface of the second protective layer 30 .

The adhesive layer may be laminated on the lower surface of the second protective layer to adhere the polarizing plate to the liquid crystal display.

The adhesive layer may be formed of a composition for an adhesive layer including a conventional adhesive resin as long as the orthogonal transmittance ratio of Equation 1 is not affected. For example, the composition for the adhesive layer may include a (meth)acrylic adhesive resin.

The adhesive layer may have a thickness of 5 μm to 100 μm, preferably 10 μm to 100 μm, and more preferably 10 μm to 30 μm. Within this range, it can be used for a polarizing plate.

The adhesive layer does not substantially affect the ratio of orthogonal transmittances in Equations 1 and 2 above.

Hereinafter, a polarizing plate according to another embodiment of the present invention will be described with reference to FIG. 2 .

Referring to FIG. 2 , the polarizing plate includes a polarizer 10, a first protective layer 20 stacked on the upper surface of the polarizer 10, and a third protective layer 20 sequentially stacked on the lower surface of the polarizer 10 from the polarizer 10. A protective layer 50 and a second protective layer 30 are included. It is substantially the same as the polarizing plate of FIG. 1 except that a third protective layer 50 is further laminated between the polarizer 10 and the second protective layer 30 .

The third protective layer may be stacked between the polarizer and the second protective layer to facilitate formation of the second protective layer while increasing mechanical strength of the polarizer. A laminate of the third protective layer and the second protective layer may be prepared by coating the composition for the second coating layer on the third protective layer and drying the composition. The laminate of the third protective layer and the second protective layer is adhered to the polarizer. The second protective layer is directly formed on the third protective layer. The “directly formed” means that no adhesive layer, adhesive layer, or adhesive layer is provided between the second protective layer and the third protective layer.

The third protective layer may include a conventional optically transparent resin film as long as it does not affect the thickness direction retardation of the above-described second protective layer. The laminate of the third protective layer and the second protective layer may be laminated to the polarizer by an adhesive layer. The adhesive layer may be formed of one or more of water-based adhesives and photocurable adhesives commonly known to those skilled in the art.

In one embodiment, the third protective layer has a different in-plane retardation Re at a wavelength of 550 nm compared to the second protective layer, for example, an in-plane retardation Re at a wavelength of 550 nm is 10 nm or less, preferably 0 nm to 5 nm, 0 nm to 3 nm optically. It may be a transparent resin film. Within this range, the polarization degree is excellent without affecting the orthogonal transmittance ratio of Equation 1 and can be used as a support for the coating layer.

In one embodiment, the third protective layer has a different thickness direction retardation Rth at a wavelength of 550 nm compared to the second protective layer, and for example, the third protective layer may have a larger thickness direction retardation Rth at a wavelength of 550 nm than the second protective layer.

For example, the third protective layer may be an optically transparent resin film having a thickness direction retardation Rth of 10 nm or less at a wavelength of 550 nm, preferably 0 nm to 5 nm or 0 nm to 3 nm. Within this range, the polarization degree is excellent without affecting the orthogonal transmittance ratio of Equation 1 and can be used as a support for the coating layer.

The third protective layer is a cellulose ester-based resin including triacetyl cellulose (TAC), a cyclic polyolefin-based resin including amorphous cyclic polyolefin (COP), a polycarbonate-based resin, polyethylene terephthalate (PET), poly Polyester-based resins, polyethersulfone-based resins, polysulfone-based resins, polyamide-based resins, polyimide-based resins, acyclic-polyolefin-based resins, including butylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, and the like; It may include a film formed of at least one of poly (meth) acrylate-based resins, polyvinyl alcohol-based resins, polyvinyl chloride-based resins, and polyvinylidene chloride-based resins, including polymethyl methacrylate resins. Not limited. Preferably, the third protective layer may be a film formed of a cellulose ester-based resin including triacetyl cellulose (TAC) or the like.

The third protective layer may have a thickness of 5 μm to 100 μm, preferably 10 μm to 100 μm, and more preferably 20 μm to 60 μm. Within this range, it can be used for a polarizing plate.

In one embodiment, the laminate of the second protective layer and the third protective layer may have a thickness direction retardation (Rth) of -50 nm to -10 nm at a wavelength of 550 nm. In the above range, the orthogonal transmittance ratio of Equation 1 may be reached, and the thinning effect of the polarizing plate may be obtained with the thin second protective layer. Preferably, the laminate of the second protective layer and the third protective layer may have an Rth of -40 nm to -10 nm or -35 nm to -15 nm at a wavelength of 550 nm.

The laminate of the second protective layer and the third protective layer may have a thickness direction retardation (Rth) of -50 nm to -5 nm at a wavelength of 480 nm. In the above range, the orthogonal transmittance ratio of Equation 1 may be reached, and the thinning effect of the polarizing plate may be obtained with the thin second protective layer. Preferably, the laminate may have an Rth of -50 nm to -10 nm, more preferably -20 nm to -30 nm at a wavelength of 480 nm.

The laminate of the second protective layer and the third protective layer may have a thickness direction retardation (Rth) of -50 nm to -5 nm at a wavelength of 660 nm. In the above range, the orthogonal transmittance ratio of Equation 1 may be reached, and the thinning effect of the polarizing plate may be obtained with the thin second protective layer. Preferably, the laminate may have an Rth of -50 nm to -10 nm, more preferably -20 nm to -30 nm at a wavelength of 660 nm.

In one embodiment, the laminate of the second protective layer and the third protective layer has a ratio of Rth at a wavelength of 480 nm to Rth at a wavelength of 550 nm according to Equation 5 below is 0 or more and 8 or less, preferably 1 or more and 3 or less, The ratio of Rth at a wavelength of 660 nm to Rth at a wavelength of 550 nm according to Equation 6 below may be 0 or more and 6 or less, preferably 0 or more and 1 or less. Through this, the polarizer can satisfy the effect of reducing the lateral visual difference:

[Equation 5]

Rth(@480nm)/Rth(@550nm)

(In Equation 5 above,

Rth (@550nm) is the phase difference in the thickness direction of the laminate of the second protective layer and the third protective layer at a wavelength of 550 nm (unit: nm),

Rth (@480nm) is the phase difference in the thickness direction of the laminate of the second protective layer and the third protective layer at a wavelength of 480 nm (unit: nm))

[Equation 6]

Rth(@660nm)/Rth(@550nm)

(In Equation 6 above,

Rth (@550nm) is the phase difference in the thickness direction of the laminate of the second protective layer and the third protective layer at a wavelength of 550 nm (unit: nm),

Rth(@660nm) is the thickness direction retardation of the laminate of the second protective layer and the third protective layer at a wavelength of 660 nm (unit: nm)).

Although not shown in FIG. 2 , the aforementioned adhesive layer may be additionally formed on the lower surface of the second protective layer 30 .

Hereinafter, a polarizing plate according to another embodiment of the present invention will be described.

Referring to FIG. 3, the polarizing plate includes a polarizer 10, a first protective layer 20 laminated on the upper surface of the polarizer, a second protective layer 30 sequentially laminated on the lower surface of the polarizer 10 from the polarizer, A third protective layer 50 is included. It is substantially the same as the polarizing plate of FIG. 2 except that the second protective layer is laminated between the polarizer and the third protective layer. Details of the third protective layer are the same as those described above with reference to FIG. 2 .

Although not shown in FIG. 3 , the aforementioned adhesive layer may be additionally formed on the lower surface of the second protective layer 30 .

Hereinafter, the liquid crystal display device of the present invention will be described.

The liquid crystal display of the present invention may include one or more of the polarizing plates of the present invention. The liquid crystal display device may include an IPS liquid crystal display device, but is not limited thereto.

In one embodiment, the liquid crystal display device includes a liquid crystal panel, a first polarizing plate disposed on an upper surface (light exit surface of the liquid crystal panel) of the liquid crystal panel, and a second polarizer disposed on a lower surface (light incident surface of the liquid crystal panel) of the liquid crystal panel. It includes a polarizing plate and a light source disposed on a lower surface of the second polarizing plate, and the first polarizing plate includes the polarizing plate of the present invention. The first polarizing plate is stacked in the order of an adhesive layer, a second protective layer, a polarizer, and a first protective layer from the liquid crystal panel. The second polarizing plate may include a conventional polarizing plate known to those skilled in the art.

In another embodiment, the liquid crystal display device includes a liquid crystal panel, a first polarizing plate disposed on the upper surface of the liquid crystal panel (light exit surface of the liquid crystal panel), and a second polarizer disposed on the lower surface (light incident surface of the liquid crystal panel) of the liquid crystal panel. It includes a polarizing plate and a light source disposed on a lower surface of the second polarizing plate, and the second polarizing plate includes the polarizing plate of the present invention. The second polarizing plate is stacked in the order of an adhesive layer, a second protective layer, a polarizer, and a first protective layer from the liquid crystal panel. The second polarizing plate may include a conventional polarizing plate known to those skilled in the art.

The light source may include a light source having a continuous emission spectrum. For example, the light source may include a white LED light source or the like.

Hereinafter, the configuration and operation of the present invention will be described in more detail through preferred embodiments of the present invention. However, the following examples are provided to aid understanding of the present invention, and the scope of the present invention is not limited to the following examples.

Example One

A polarizer (thickness: 17 μm) was prepared by stretching a polyvinyl alcohol film (VF-PE#4500, Kuraray, thickness: 45 μm) about 6 times through swelling, iodine dyeing, and crosslinking.

A polyethylene terephthalate film (Toyobo, SRF, thickness: 80 μm, wavelength: 550 nm, Re: 8500 nm, Rth: 9300 nm, NZ: 1.54) was attached to the light exit surface of the polarizer as a first protective layer. An angle between the absorption axis of the polarizer and the slow axis of the first protective film is 0°.

A triacetyl cellulose film (Konica, Z-TAC, thickness: 40 μm, wavelength: 550 nm, Re: 0.1 nm, Rth: 0 nm) was used as the third protective layer.

A coating layer composition for the second protective layer was prepared by mixing cellulose acetate propionate (VM-512, Eastman Co.) and methyl ethyl ketone as a solvent.

A laminate of the third protective layer and the second protective layer was prepared by coating the composition for the coating layer for the second protective layer prepared above to a predetermined thickness on one surface of the third protective layer and drying it. The laminate of the third protective layer and the second protective layer has an Rth of -15 nm at a wavelength of 550 nm.

A laminate of the third protective layer and the second protective layer was attached to the light incident surface of the polarizer so that the second protective layer and the third protective layer were sequentially laminated from the polarizer. Accordingly, a polarizing plate was manufactured by stacking the first protective layer - polarizer - second protective layer - third protective layer in this order.

Example 2 to Example 3

In Example 1, by changing the thickness of the second protective layer when forming the second protective layer, Rth at a wavelength of 550 nm of the second protective layer and Rth of a laminate of the second protective layer and the third protective layer at a wavelength of 550 nm are calculated in the table below. A polarizing plate was manufactured in the same manner as in Example 1 except for changing as in 1.

Example 4

In Example 1, a polarizer in which the first protective layer, the polarizer, and the second protective layer are sequentially stacked was prepared by directly coating the composition for the coating layer for the second protective layer on the polarizer to form the second protective layer.

comparative example One

In Example 1, a polarizing plate was manufactured in the same manner as in Example 1 except that the first protective layer, the polarizer, and the third protective layer were laminated in that order without the second protective layer.

comparative example 2

In Example 1, by changing the thickness of the second protective layer when forming the second protective layer, Rth at a wavelength of 550 nm of the second protective layer and Rth of a laminate of the second protective layer and the third protective layer at a wavelength of 550 nm are calculated in the table below. A polarizing plate was manufactured in the same manner as in Example 1 except for changing as in 1.

comparative example 3

In Example 1, by changing the thickness of the second protective layer when forming the second protective layer, Rth at a wavelength of 550 nm of the second protective layer and Rth of a laminate of the second protective layer and the third protective layer at a wavelength of 550 nm are calculated in the table below. A polarizing plate was manufactured in the same manner as in Example 1 except for changing as in 1.

The phase difference (unit: nm) of Examples and Comparative Examples was measured using Axoscan.

Orthogonal transmittance (Tc, unit: %) was measured using JASCO V7100 at a wavelength of 420 nm to 720 nm for the polarizers prepared in Examples and Comparative Examples, and the results are shown in Table 1 and FIG. 4 below. As shown in FIG. 4, Examples 1 to 3 had higher orthogonal transmittance at a wavelength of 480 nm than Comparative Example 1.

Example comparative example One 2 3 4 One 2 3 Rth of the second protective layer -15 -25 -35 -25 - -5 -101 Rth of the laminate of the second protective layer and the third protective layer -15 -25 -35 -25 0 -5 -101 Tc @480nm 0.004 0.005 0.006 0.006 0.0018 0.0019 0.011 @660nm 0.001 0.001 0.001 0.001 0.001 0.001 0.001 @700nm 0.010 0.011 0.012 0.011 0.010 0.010 0.010 Equation 1 4 5 6 6 1.8 1.9 11 Equation 2 10 11 12 11 10 10 10

The polarizing plates prepared in Examples and Comparative Examples were assembled as a viewing-side polarizing plate of IPS liquid crystal. Using the EZ-Contrast XL-88 equipment, left and right visual perception was evaluated at a polar angle of 45° and azimuth angle of 45°/135° in black mode. It was evaluated as poor when the visual difference between the left side and the right side was confirmed with the naked eye, and good when the visual difference was hardly confirmed. The visual difference was calculated by calculating the distance between the left side color coordinate value (x, y) point and the right side color coordinate value (x, y) point. The lower the difference in visual perception means that there is no difference in visual perception between the left side and the right side in the black mode. For the polarizers prepared in Examples and Comparative Examples, the degree of polarization was measured using a JASCO V7100 device. The results are shown in Table 2 and FIG. 5 below.

left side right side visual difference degree of polarization
(%) x y x y Example 1 0.243 0.267 0.317 0.307 0.08 99.995 Example 2 0.243 0.268 0.282 0.267 0.04 99.994 Example 3 0.244 0.267 0.262 0.243 0.03 99.993 Example 4 0.243 0.262 0.279 0.263 0.04 99.994 Comparative Example 1 0.224 0.223 0.366 0.364 0.20 99.996 Comparative Example 2 0.224 0.223 0.360 0.359 0.19 99.996 Comparative Example 3 0.244 0.248 0.249 0.243 0.01 99.8

As shown in Table 2 and FIG. 5, the polarizer of the present invention reduced the luminous difference of both sides in the black mode and had a polarization degree of 99.9% or more.

On the other hand, as shown in Table 2 and FIG. 5, Comparative Example 1 without the second protective layer itself had a higher luminous difference than the present invention. In addition, Comparative Example 2 having a second protective layer but having a transmittance ratio of less than 2 in Equation 1 had a higher luminous difference than that of the present invention. In addition, Comparative Example 2 having a second protective layer but having a transmittance ratio of more than 10 in Equation 1 had a degree of polarization of less than 99.9%, and thus could not perform the original function of a polarizing plate.

Simple modifications or changes of the present invention can be easily performed by those skilled in the art, and all such modifications or changes can be considered to be included in the scope of the present invention.

Claims (20)

polarizer,
A first protective layer laminated on the upper surface of the polarizer, and
A polarizing plate including a second protective layer laminated on the lower surface of the polarizer,
The polarizing plate has an orthogonal transmittance ratio of 2 or more and 10 or less, represented by Equation 1 below:
[Equation 1]
Ratio of orthogonal transmittance = Tc(@480nm)/Tc(@660nm)
(In Equation 1, Tc(@660nm) is the orthogonal transmittance (unit: %) at a wavelength of 660nm of the polarizer,
Tc (@480nm) is orthogonal transmittance (unit: %) at a wavelength of 480nm of the polarizer,
The polarizing plate has a ratio of orthogonal transmittance represented by Equation 2 below greater than 1 and less than or equal to 20, and
[Equation 2]
Ratio of orthogonal transmittance = Tc(@700nm)/Tc(@660nm)
(In Equation 2 above,
Tc (@660nm) is the orthogonal transmittance (unit: %) at a wavelength of 660nm of the polarizer,
Tc (@700nm) is orthogonal transmittance (unit: %) at a wavelength of 700nm of the polarizer,
In the second protective layer, the ratio according to Equation 3 below is 0 or more and 8 or less, and the ratio according to Equation 4 below is 0 or more and 6 or less:
[Equation 3]
Rth(@480nm)/Rth(@550nm)
(In Equation 3 above,
Rth (@550nm) is the phase difference in the thickness direction of the second protective layer at a wavelength of 550nm (unit: nm),
Rth (@480nm) is the phase difference in the thickness direction of the second protective layer at a wavelength of 480nm (unit: nm)
[Equation 4]
Rth(@660nm)/Rth(@550nm)
(In Equation 4 above,
Rth (@550nm) is the phase difference in the thickness direction of the second protective layer at a wavelength of 550nm (unit: nm),
Rth (@660nm) is the phase difference in the thickness direction of the second protective layer at a wavelength of 660nm (unit: nm),
The polarizing plate has an orthogonal transmittance of 0.001% or more and 0.01% or less at a wavelength of 480 nm,
The polarizing plate has an orthogonal transmittance of 0.0005% or more and 0.01% or less at a wavelength of 660 nm,
The polarizing plate has an orthogonal transmittance of 0.001% or more and 0.02% or less at a wavelength of 700 nm.
The polarizing plate according to claim 1, wherein a ratio of orthogonal transmittance represented by Equation 1 is 2 or more and 8 or less.
delete delete The polarizing plate according to claim 1, wherein a ratio of orthogonal transmittance represented by Equation 2 is greater than 1 and less than or equal to 15.
delete The polarizing plate according to claim 1, wherein the second protective layer is laminated on the light incident surface of the polarizer.
The polarizing plate of claim 1, wherein the second protective layer has a thickness direction retardation (Rth) of -60 nm to +10 nm at a wavelength of 550 nm.
The polarizing plate of claim 1, wherein the second protective layer has an in-plane retardation Re of 0 nm to 10 nm at a wavelength of 550 nm.
The polarizing plate of claim 1, wherein the second protective layer is formed of a composition for a cellulose ester-based coating layer.
The polarizing plate of claim 10, wherein the composition includes a cellulose ester-based compound including at least one of cellulose acetate (CA), cellulose acetate propionate (CAP), and cellulose acetate butyrate (CAB).
11. The polarizing plate of claim 10, wherein the composition further comprises an additive having a fused ring.
The polarizing plate according to claim 12, wherein the additive having the fused ring has an aromatic group.
The polarizing plate according to claim 1, wherein the first protective layer has an in-plane retardation Re of 8,000 nm or more at a wavelength of 550 nm.
The method of claim 1, wherein when the absorption axis of the polarizer is 0 °, the angle between the slow axis of the first protective layer and the absorption axis of the polarizer is -5 ° to +5 °, polarizer.
The polarizing plate of claim 1 , wherein a third protective layer is further laminated on a lower surface of the second protective layer.
The polarizing plate of claim 16 , wherein the laminate of the second protective layer and the third protective layer has a thickness direction retardation (Rth) of -50 nm to -10 nm at a wavelength of 550 nm.
The polarizing plate of claim 16, wherein the third protective layer has an in-plane retardation Re of 10 nm or less at a wavelength of 550 nm.
The polarizing plate of claim 16 , wherein the third protective layer has a different retardation Rth in the thickness direction at a wavelength of 550 nm than that of the second protective layer.
A liquid crystal display device comprising the polarizing plate of any one of claims 1, 2, 5, and 7 to 19.

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