KR20220154458A - Polarizing plate and image display device comprising the same - Google Patents

Abstract

The present invention is a polarizing plate comprising a first protective film, a polarizer, and a second protective film. The present invention relates to the polarizing plate and an image display device including the same, wherein the second protective film includes an acrylic film having a tensile modulus of elasticity in a machine direction (MD) of 1.4 to 1.6 GPa under high temperature and high humidity conditions, and the tensile modulus of elasticity in the machine direction (MD) under high temperature and high humidity conditions of the first protective film is greater than or equal to the elastic modulus of the second protective film under the high temperature and high humidity condition. The polarizing plate and image display device including the same can reduce a light leakage phenomenon of a liquid crystal display that may occur due to a bending phenomenon by reducing the bending phenomenon of the polarizing plate in a high temperature or high humidity environment.

Description

Polarizing plate and image display device having the same {POLARIZING PLATE AND IMAGE DISPLAY DEVICE COMPRISING THE SAME}

The present invention relates to a polarizing plate and an image display device having the same, and more specifically, to a polarizing plate including a structure in which a first protective film, a polarizer, and a second protective film are laminated, in the machine direction of the first protective film (MD, It relates to a polarizing plate capable of preventing warpage and light leakage by forming the modulus of elasticity of machine direction (Machine Direction) to be greater than or equal to the modulus of elasticity of the machine direction (MD) of the second protective film, and an image display device having the same.

Liquid crystal displays are widely used as optical display devices due to their low power consumption, small volume and light weight. In general, a liquid crystal display has a basic configuration in which polarizers are installed on both sides of a liquid crystal cell, and the characteristics of transmitted light emitted through the polarizer are changed to achieve light visualization.

In general, a polarizer protective film serving as a protective film is attached to both sides of the polarizer through an adhesive. A polarizer obtained by adsorbing iodine or a dichroic dye to a hydrophilic polymer such as polyvinyl alcohol (PVA) and then stretching and aligning the polarizer is used. A polarizer protective film is used to increase durability and mechanical properties of the polarizer, and it is important for the protective film to maintain optical characteristics such as polarization characteristics of the polarizer. Therefore, the polarizer protective film is required to be optically transparent and isotropic.

The polarizer including the polyvinyl alcohol-based material usually has a polarization function by orienting internal molecular arrangements in a predetermined direction by stretching a film for forming the polarizer. Therefore, the stretching process is an essential process when manufacturing a polarizer. However, such a stretching process causes a contraction force to be expressed later in an environment where heat is generated by a high temperature or high humidity or a peripheral element in the polarizer, and the polarizer is deformed by such contraction force.

When the polarizing plate including the protective film is attached to a liquid crystal display device, the polarizing plate including the polarizer may contract or expand according to changes in the surrounding environment. In addition, the polarizer may warp due to heat generated while driving the liquid crystal display or when the driving environment is at high temperature or high humidity. Problems such as light leakage of the liquid crystal display may occur.

In this regard, Korean Patent Publication No. 10-2014-0146902 discloses an optical film having a tensile modulus of elasticity in the machine direction of 1.8 GPa to 2.3 GPa, but under conditions of extreme high temperature and high humidity of 60 ° C and 90%, panel warpage or The light leakage suppression-related effect is not sufficient.

Republic of Korea Patent Publication No. 10-2014-0146902

The present invention is to solve the above problems, to provide a polarizing plate that prevents light leakage caused by bending of the protective film.

In order to solve the above problems, the present invention is a polarizing plate including a first protective film, a polarizer and a second protective film, wherein the second protective film has a tensile modulus of elasticity in the machine direction (MD) of 1.4 to 1.6 under high temperature and high humidity conditions. Provides a polarizing plate comprising an acrylic film of GPa, characterized in that the tensile modulus of elasticity in the machine direction (MD) of the first protective film at high temperature and high humidity is greater than or equal to the modulus of elasticity at high temperature and high humidity of the second protective film do.

In addition, the present invention provides an image display device having a polarizing plate.

The polarizing plate of the present invention can reduce the warping of the polarizing plate in a high temperature or high humidity environment by adjusting the modulus of elasticity of the upper protective film and the lower protective film, thereby reducing the light leakage phenomenon of the liquid crystal display that may occur due to the warping phenomenon. In addition, by reducing the warpage, it is possible to prevent deterioration in image quality such as non-uniform luminance of the liquid crystal display in a high temperature and high humidity environment.

1 is a cross-sectional view of a polarizing plate according to an embodiment of the present invention.
2 is a conceptual diagram of warpage measurement in the present invention.
3 is a conceptual diagram of light leakage measurement in the present invention.

Hereinafter, preferred embodiments of the present invention will be described. However, the embodiments of the present invention can be modified in many different forms, and the scope of the present invention is not limited to the embodiments described below. In addition, the embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

< Polarizer >

The polarizer 100 of the present invention includes a first protective film 120, a polarizer 110, and a second protective film 130, and may further include an adhesive 140 on one or both surfaces of each layer.

Referring to FIG. 1 , a polarizing plate 100 according to an embodiment of the present invention has a structure in which a first protective film 120, a polarizer 110, a second protective film 130, and an adhesive 140 are stacked. It can be.

Polarizer (110)

The polarizer 110 according to the present invention is an optical film that serves to change incident natural light into a desired single polarization state (linear polarization state), and can be used by swelling, dyeing, crosslinking, stretching, washing, drying, etc. It may be a polarizer commonly used in the art manufactured according to a process including the step.

The type of the polarizer 110 is not particularly limited as long as it is a dichroic material, that is, a film that can be dyed with iodine. For example, a polyvinyl alcohol (PVA) film, a dehydrated polyvinyl alcohol film, a dehydrochlorinated film A polyvinyl alcohol film, a polyethylene terephthalate film, an ethylene-vinyl acetate copolymer film, an ethylene-vinyl alcohol copolymer film, a cellulose film, and a partially saponified film thereof. Among these, a polyvinyl alcohol-based film is preferable in that it has an excellent effect of reinforcing the uniformity of polarization degree in the plane and an excellent dyeing affinity for iodine.

The polyvinyl alcohol-based resin constituting the polarizer 110 can be produced by saponifying polyvinyl acetate-based resin. The degree of saponification of the polyvinyl alcohol-based resin may be 85 to 100 mol%, preferably 90 mol% or more, and more preferably 98 to 100 mol%.

Examples of polyvinyl acetate-based resins include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable with vinyl acetate. Specific examples of the other monomer copolymerizable with the vinyl acetate include unsaturated carboxylic acids, unsaturated sulfonic acids, olefins, unsaturated amines, vinyl ethers, and acrylamides having an ammonium group.

In addition, the polyvinyl alcohol-based resin may be modified, and for example, polyvinyl formal, polyvinyl acetal, or polyvinyl butyral modified with aldehydes may be used.

The polymerization degree of the polyvinyl alcohol-based resin is usually 1,000 to 10,000, preferably 1,500 to 5,000.

The polyvinyl alcohol-based resin may be formed into a film and used as a polarizer. A method for forming a film of polyvinyl alcohol-based resin is not particularly limited, and various methods known in the art may be used. For example, the process of uniaxially stretching a polyvinyl alcohol-type resin film; dyeing the stretched film with a dichroic dye to adsorb the dye; A step of treating the film to which the dye is adsorbed with an aqueous solution of boric acid; And it can be prepared through a process of washing with water. At this time, iodine or a dichroic organic dye may be used as the dichroic dye.

The contractive force of the polarizer 110 according to the present invention is preferably 2.5 N to 3.5 N, in terms of preventing light leakage.

The polarizer 110 according to the present invention may have a thickness of 5 to 40 μm, preferably 8 to 25 μm. When the thickness of the polarizer is less than 5 μm, there is a problem of lack of fairness and mass productivity during the polarizer stretching process, and when the thickness exceeds 40 μm, a problem that thinning of the polarizing plate may not be achieved may occur.

The surface of the polarizer 110 is preferably modified by at least one of corona treatment and plasma treatment. Foreign substances on the surface of the polarizer can be removed through the corona treatment or plasma treatment, and coating properties can be increased. If the surface of the polarizer is not modified, coating properties may deteriorate, and adhesive residues and stains may occur during the peeling process.

Surface treatment layers such as a hard coating layer, an antireflection layer, an antiglare layer, and an antistatic layer may be further laminated on one side or both sides of the polarizer 110 as needed. In addition, an optical functional film may be further laminated by the pressure-sensitive adhesive layer. As an optical functional film, for example, an optical compensation film in which a liquid crystalline compound or a polymer compound thereof is oriented on the surface of a substrate, a reflective polarization film that transmits some kind of polarized light and reflects polarized light of the opposite nature. A separation film, a retardation film containing a polycarbonate resin, a retardation film containing a cyclic polyolefin resin, an anti-glare function additional film having a concavo-convex shape on the surface, an additional film having a surface antireflection treatment, a reflective film having a reflective function on the surface, and a transflective reflective film having both a reflective function and a transmissive function.

First protective film 120 and second protective film 130

The polarizing plate of the present invention includes a first protective film 120 and a second protective film 130 as a protective film serving as a protective substrate for the polarizer.

In the present invention, the second protective film 130 has a tensile modulus of elasticity in the machine direction (MD) of 1.4 to 1.6 GPa under high temperature and high humidity conditions, and the machine direction of the first protective film 120 under high temperature and high humidity conditions. The tensile modulus of elasticity in the direction (MD) is greater than or equal to the tensile modulus of elasticity in the machine direction (MD) under high temperature and high humidity conditions of the second protective film 130 .

Specifically, the tensile modulus ratio in the machine direction of the first protective film 120 and the second protective film 130 under high temperature and high humidity conditions may be 1:1 to 3:1, preferably 1:1 to 2.2. : can be 1.

In the present invention, when the modulus of elasticity of the first protective film 120 and the second protective film 130 satisfies the above conditions, in particular, in a high temperature or high humidity environment, the warpage of the polarizer is reduced, which can be caused by warpage. It is characterized by experimentally confirming that the light leakage phenomenon of a liquid crystal display device can be reduced.

On the other hand, in the case of the elastic modulus measured at room temperature (25 ° C.), which is conventionally measured, the elastic modulus conditions of the first and second protective films according to the present invention and the resulting warpage and light leakage prevention effect do not appear You can check.

in the high temperature and high humidity conditions. The high temperature may be 40 °C or higher, preferably 60 °C. In addition, the high humidity may be 85% or more, preferably 90%.

In addition, under high temperature and high humidity conditions, the first protective film 120 preferably has a tensile modulus of elasticity of 1.4 to 3.3 GPa in the machine direction (MD) and a tensile modulus of elasticity of 1.4 to 6.4 GPa in the transverse direction (TD). do. When the range of tensile modulus is satisfied, it is preferable in terms of preventing light leakage, and in this case, the modulus of elasticity of the first protective film at high temperature and high humidity in the machine direction (MD) is greater than the modulus of elasticity of the second protective film at high temperature and high humidity. should be the same

The first protective film 120 may serve as a protective substrate for the polarizing plate. The first protective film 120 is attached to the upper surface of the polarizer 110 to protect the polarizer 110 from the effects of heat and moisture. The first protective film 120 may include at least one of optically transparent protective films, and is not particularly limited as long as it has excellent transparency, mechanical strength, thermal stability, moisture barrier properties, and isotropy.

Specifically, the first protective film 120 is a polymer obtained by condensation polymerization of a dibasic acid and a dihydric alcohol, a polyester-based resin film such as polyethylene terephthalate, polyethylene isophthalate, and polybutylene terephthalate;

cellulosic resin films such as diacetyl cellulose and triacetyl cellulose;

A polycarbonate-based resin film obtained by condensation polymerization of bisphenol A and phosgene, which is a polymer having a carbonate bond in the main chain;

acrylic resin films such as polymethyl (meth)acrylate and polyethyl (meth)acrylate, which are homopolymers of methyl methacrylate or copolymers of methyl methacrylate and acrylic acid esters such as methyl acrylate;

styrenic resin films such as polystyrene and acrylonitrile-styrene copolymer;

polyolefin resin films such as cycloolefin, cycloolefin copolymer, polynorbornene, polypropylene, polyethylene, and ethylenepropylene copolymer;

Vinyl chloride-based film; polyamide-based resin films such as nylon and aromatic polyamide;

Other imide-based resin films; sulfone-based resin film; polyethersulfone-based resin film; polyether ketone-based resin film; Sulfurized polyphenylene-based resin film; vinyl alcohol-based resin film; vinylidene chloride-based resin film; vinyl butyral-based resin film; allylate-based resin films; polyoxymethylene-based resin film; Urethane-based resin film; Epoxy-based resin film; Alternatively, a silicone-based resin film may be used, and preferably a cellulose-based resin film such as triacetyl cellulose (TAC) may be used.

The second protective film 130 is attached to the lower surface of the polarizer 110 and serves to protect the polarizer 110 and compensate for phase. The second protective film 130 is a protective film disposed on the side of the liquid crystal display when the polarizer is applied to the liquid crystal panel.

The second protective film 130 has a tensile modulus of elasticity of 1.4 to 1.6 GPa in the machine direction (MD) and a tensile modulus of elasticity of 1.4 to 2.2 GPa in the transverse direction (TD) under high temperature and high humidity conditions. desirable.

The second protective film 130 may include one or more of optically transparent protective films, and is not particularly limited as long as it has excellent transparency, mechanical strength, thermal stability, moisture barrier property, and isotropy, but is not particularly limited. In order to satisfy the tensile modulus, it is preferable to use an acrylic resin film in terms of preventing light leakage.

The acrylic resin preferably includes a methyl methacrylate-based resin containing 50 to 100% by weight of methyl methacrylate repeating units. When the content of methyl methacrylate in the acrylic resin satisfies the above range, it is preferable in terms of roles such as transparency and shielding properties as a protective film. Specific examples of the methyl methacrylate-based resin include polymethyl methacrylate (PMMA) resin.

In addition, the acrylic resin may include a resin copolymerized with methyl methacrylate and other monomers.

As a copolymerizable monomer, for example, ethyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, benzyl methacrylate, 2-ethylhexyl methacrylate, methacrylic acid-2 -Methacrylic acid esters such as hydroxyethyl; acrylic esters such as methyl acrylate, ethyl acrylate, butyl acrylate, cyclohexyl acrylate, phenyl acrylate, benzyl acrylate, 2-ethylhexyl acrylate, and 2-hydroxyethyl acrylate; unsaturated acids such as methacrylic acid and acrylic acid; halogenated styrenes such as chlorostyrene and bromostyrene; substituted styrenes such as alkyl styrenes such as vinyltoluene and α-methylstyrene; Acrylonitrile, methacrylonitrile, maleic anhydride, phenyl maleimide, cyclohexyl maleimide, etc. are mentioned. These monomers can be used individually or in combination of two or more.

In addition, the upper protective film may include a rubbery copolymer to increase the elastic modulus.

The rubbery copolymer is largely divided into two types: an acrylic multilayer structure polymer and a graft copolymer, and these may be included individually or in combination.

Preferably, the thickness of the first protective film 120 is 40 μm to 80 μm, and the thickness of the second protective film 130 is 20 μm to 50 μm in terms of panel warpage and light leakage prevention. , Problems such as generation of wrinkles or stains due to excessive drying may occur during bonding of the polarizer, and stains may occur due to remaining moisture due to difficulty in drying.

In addition, the ratio of the thickness of the first protective film to the thickness of the second protective film is preferably 1:1 to 2:1 in terms of panel warpage and light leakage prevention.

Adhesive (140)

The polarizing plate of the present invention may further include an adhesive 140, and the adhesive 140 may be included for bonding of each layer included in the polarizing plate of the present invention. For example, the second protective film 130 It includes what is formed for bonding with a liquid crystal display device on the surface. The adhesive 140 may be, for example, a (meth)acrylic adhesive, a urethane-based adhesive, a silicone-based adhesive, a polyester-based adhesive, a polyamide-based adhesive, a polyether-based adhesive, a fluorine-based adhesive, a rubber-based adhesive, and the like. From the viewpoint of reliability, reworkability, etc., a (meth)acrylic pressure-sensitive adhesive is preferably used.

The adhesive 140 may have a viscosity of 5 to 100 cP. When included within the above range, spreadability on the surface of the polarizer is secured, and fairness can be secured in a slit coater, a slit die coater, and the like.

The thickness of the adhesive 140 is not particularly limited, but may be preferably 10 nm to 200 nm.

The application of the pressure-sensitive adhesive 140 may be performed on either the protective film or the polarizer or on both of them, and in general, a drying treatment is performed after adhesion to form an adhesive layer including an applied drying layer.

The bonding method of the polarizer and the protective film using the adhesive 140 is not particularly limited, and for example, the polarizer and / or protection by a casting method, a Mayer bar coating method, a gravure coating method, a die coating method, a dip coating method, a spraying method, A method of applying the pressure-sensitive adhesive 140 to the adhesive surface of the film and overlapping the two is exemplified.

< Image display device >

The polarizing plate described above can be employed and usefully used in an image display device in which the polarizing plate can be used.

Specifically, the polarizer according to the present invention is an image display device (display device), specifically a TN (twisted nematic), HTN (highly twisted nematic) or STN (excessive twisted nematic) mode display, AMD-TN ( active matrix induced TN) displays, IPS (in-plane switching) mode displays, DAP (aligned phase transformation) or VA (vertically aligned) mode displays such as ECB (electrically controlled birefringence), CSH (color super homeotropic) ), VAN or VAC (vertically aligned nematic or cholesteric) displays, MVA (multi-domain vertically aligned) displays, bending mode displays or hybrid displays such as OCB (optically compensated bending cells or optically compensated birefringent), R-OCB (reflective OCB), HAN (hybrid aligned nematic) or pi-cell displays or organic light emitting diodes (OLEDs).

The polarizing plate according to the present invention is particularly preferably used in a reflective or transmissive liquid crystal display (LCD) or organic light emitting diode (OLED) to prevent image quality deterioration such as luminance non-uniformity of an image display device in a high temperature and high humidity environment. can For example, it is disposed in a liquid crystal display device to prevent bending of the panel to prevent light leakage, and consequently, to prevent deterioration of image quality.

Other configurations of an image display device such as a liquid crystal display (LCD) may adopt conventional general configurations as they are, except that the polarizer according to the present invention is used in the position of the conventional polarizer.

As above, the present invention has been described in detail with reference to the embodiments of the present invention. For those skilled in the art, these specific techniques are only preferred embodiments, and thus the scope of the present invention is limited. It is clear that it will not be For example, when the polarizer and the protective film are disposed on the polarizer of the present invention, an additional retardation plate, a hard coating layer, a touch panel, and the like may be disposed above or below the polarizer.

Hereinafter, the present invention will be described in more detail using Examples and Comparative Examples. However, the following examples are intended to illustrate the present invention, and the present invention is not limited by the following examples, and may be variously modified and changed. The scope of the present invention will be determined by the technical spirit of the claims to be described later.

<Manufacture of polarizing plate>

Manufacture of polarizer

As shown in Table 1 below, high shrinkage force polarizers and low shrinkage force polarizers having different shrinkage forces were prepared using a polyvinyl alcohol (PVA) resin. The polarizer used was a polarizer produced in our company's (Dongwoo Fine-Chem) mass production line, and the thickness of the polarizer was less than 25 μm, the degree of polarization was 99% or more, and the transmittance was 40% or more.

composition PVA shrinkage high shrinkage 3.5N low shrinkage 2.5N

Manufacture of protective film

As the first or second protective film, protective materials 1 to 8 according to Table 2 below were used. According to the embodiment, the protective material is machine direction (MD, Machine Direction) elastic modulus and transverse using a Universal Testing Machine (UTM) in accordance with JIS-K6251-1 standard under thickness and high temperature / high humidity (60 ℃ / 90%) environmental conditions. Transverse Direction (TD) tensile modulus was measured, and the measured thickness and modulus values are shown in Table 2 below.

Composition of protective film Thickness (㎛) High temperature/high humidity (60℃/90%)
Tensile Modulus (GPa) MD TD protective material 1 Acrylic Film
(LG Chem) 40 1.5 1.4 protective material 2 TAC Film
(Konica recipe) 40 2.4 2.0 protective material 3 TAC Film
(Fuji system) 60 3.3 3.2 protective material 4 PET Film
(Toyobo system) 80 2.2 6.4 protective material 5 Acrylic Film
(Dongwoo Fine-Chem) 60 0.5 0.5 protective material 6 Acrylic Film
(Dongwoo Fine-Chem) 50 1.2 1.3 protective material 7 TAC Film
(Konica recipe) 40 1.7 1.6 protective material 8 Acrylic Film
(Dongwoo Fine-Chem) 60 0.5 0.5

<Example 1>

A polarizer having a low shrinkage force of 2.5 N and protective substrate 1 as a first protective film, and a 40 μm thick acrylic film (product name: GA01, manufactured by LG Chemicals, high temperature / high humidity (60 ° C / 90%) elastic modulus 1.5 GPa) was used as the second protective film, and as an adhesive, 3 parts by weight of acetoacetyl group-modified polyvinyl alcohol resin (Cosenol Z200, Japan Synthetic Chemical Industry Co., Ltd.) and 1.5 parts by weight of glyoxal crosslinking agent were added to 100 parts by weight of water (distilled water). The pressure-sensitive adhesive 140 was prepared by adding 0.3 parts by weight of polyethylene-modified polydimethylsiloxane (BYK-348, manufactured by BYK) based on 100 parts by weight of the polyvinyl alcohol-based resin (based on solid content). A polarizing plate was manufactured by adhering each component with the adhesive 140.

<Example 2>

A polarizing plate was manufactured in the same manner as in Example 1, except that the polarizer having a low shrinkage force of 2.5 N and the protective substrate 2 were used as the first protective film.

<Example 3>

A polarizing plate was manufactured in the same manner as in Example 1, except that the polarizer having a high shrinkage force of 3.5 N and the protective substrate 2 were used as the first protective film.

<Example 4>

A polarizing plate was manufactured in the same manner as in Example 1, except that the polarizer having a low shrinkage force of 2.5 N and the protective substrate 3 were used as the first protective film.

<Example 5>

A polarizing plate was manufactured in the same manner as in Example 1, except that the polarizer having a low shrinkage force of 2.5 N and the protective substrate 4 were used as the first protective film.

<Example 6>

A polarizing plate was manufactured in the same manner as in Example 1, except that a polarizer having a high shrinkage force of 3.5 N and protective substrate 1 was used as the first protective film.

<Comparative Example 1>

A polarizing plate was manufactured in the same manner as in Example 1, except that the polarizer having a low shrinkage force of 2.5 N and the protective substrate 5 were used as the first protective film.

<Comparative Example 2>

A polarizing plate was prepared in the same manner as in Example 1, except that a polarizer having a low shrinkage force of 2.5 N, protective material 5 as the first protective film, and protective material 6 as the second protective film.

<Comparative Example 3>

A polarizing plate was prepared in the same manner as in Example 1, except that a polarizer having a low shrinkage force of 2.5 N, protective material 5 as the first protective film, and protective material 7 as the second protective film.

<Comparative Example 4>

A polarizing plate was prepared in the same manner as in Example 1, except that a polarizer having a low shrinkage force of 2.5 N, protective material 5 as the first protective film, and protective material 8 as the second protective film.

Experimental Example 1: Warpage measurement

In the method shown in FIG. 2, the bending height (H) of the glass plate 500 attached with the polarizing plate manufactured in Examples 1 to 6 and Comparative Example of the present invention is measured from the bottom 600, respectively, and the warpage of the panel ( Bending) was evaluated. Specifically, the polarizers of Examples 1 to 6 and Comparative Example were attached to both sides of a glass plate having a thickness of 0.3 cm and cut into A x B in the machine direction and the direction perpendicular to the machine direction, respectively, and then 40 ° C., 90% relative humidity. After leaving it in the chamber for 48 hours, leaving it at 25 ° C. and 55% relative humidity for 2 hours, the warpage was measured, measured and shown in Table 3.

Experimental Example 2: Light leakage measurement

As shown in FIG. 3, specimens were prepared by attaching the polarizing plates (a, c) prepared in Examples 1 to 6 and Comparative Example to both sides of a glass substrate (b) such that their absorption axes were perpendicular to each other. The prepared specimen was left for 48 hours in a chamber with a relative humidity of 90%, and then left for 2 hours at 25 °C and a relative humidity of 55%. After driving the liquid crystal display using the specimen, it was evaluated according to the following criteria, and the results are shown in Table 3.

<Evaluation Criteria>

◎: When no difference in luminance is observed during visual observation, the light leakage phenomenon cannot be recognized.

○: When the luminance difference is weakly recognized and the light leakage is very weak when visually observed

△: When there is a slight difference in luminance upon visual observation, and light leakage is recognized

×: When there is a significant luminance difference and severe light leakage when visually observed

Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 of the first protective film
MD direction
High temperature/high humidity (60/90%)
Tensile Modulus (GPa) 1.5 2.4 2.4 3.3 2.2 1.5 0.5 0.5 0.5 0.5 of the first protective film
TD direction
High temperature/high humidity (60/90%)
Tensile Modulus (GPa) 1.4 2.0 2.0 3.2 6.4 1.4 0.5 0.5 0.5 0.5 of the first protective film
MD direction
Normal temperature (25℃)
Tensile Modulus (GPa) 2.2 3.2 3.2 3.6 3.2 2.2 1.5 1.8 2.2 0.5 Polarizer contraction force (N) 2.5 2.5 3.5 2.5 2.5 3.5 2.5 2.5 2.5 2.5 of the 2nd protective film
MD direction
High temperature/high humidity (60/90%)
Tensile Modulus (GPa) 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.2 1.7 0.5 Panel warpage (mm) 0.9 0.2 0.6 0.1 0.1 1.4 2.6 2.7 2.4 2.7 level of light ○ ◎ ○ ◎ ◎ △ X X X X

As can be seen from the results of <Table 3>, the modulus of elasticity in the machine direction (MD) high temperature/high humidity (60°C/90%) of the first protective film is as in the present invention, in the machine direction (MD) high temperature/high humidity (MD) of the second protective film. It can be seen that when the elastic modulus is greater than or equal to the high humidity (60℃/90%), the warpage value of the panel is as small as 1.4 mm or less, and thus the panel warpage phenomenon can be effectively suppressed. Specifically, it can be seen that the curvature of the panel is more effectively suppressed under a high-temperature/high-humidity environment than under conditions at room temperature. On the other hand, in the case of the comparative example, it can be seen that the panel warpage value is 2.4 to 2.7 mm, which is very large compared to the example. On the other hand, in the case of the elastic modulus measured at room temperature (25 ° C.), which is conventionally measured, the elastic modulus conditions of the first and second protective films according to the present invention and the resulting warpage and light leakage prevention effect do not appear You can check.

In addition, when such a polarizing plate is applied to a liquid crystal panel, it can be seen that warpage of the entire panel due to heat generated while driving the liquid crystal display device is reduced, and light leakage is effectively suppressed.

Claims (11)

A polarizing plate comprising a first protective film, a polarizer and a second protective film,
The second protective film includes an acrylic resin film having a tensile modulus of elasticity in a machine direction (MD) of 1.4 to 1.6 GPa under high temperature and high humidity conditions,
The tensile modulus of elasticity in the machine direction (MD) under high temperature and high humidity conditions of the first protective film is greater than or equal to the tensile modulus of elasticity in the machine direction (MD) of the second protective film under high temperature and high humidity conditions.
According to claim 1,
A polarizing plate, characterized in that the ratio of the modulus of elasticity of the first protective film at high temperature and high humidity in the machine direction (MD) and the modulus of elasticity of the second protective film at high temperature and high humidity is 1: 1 to 3: 1.
According to claim 1,
A polarizing plate, characterized in that the machine direction (MD) tensile modulus of the first protective film is 1.4 to 3.3 GPa under high temperature and high humidity conditions.
According to claim 1,
The first protective film is a polarizing plate, characterized in that it comprises a cellulose-based resin film.
According to claim 1,
The polarizing plate, characterized in that the ratio of the thickness of the first protective film and the thickness of the second protective film is 1: 1 to 2: 1.
According to claim 1,
The polarizing plate, characterized in that the thickness of the first protective film is 40 ㎛ to 80 ㎛.
According to claim 1,
The polarizing plate, characterized in that the shrinkage force of the polarizer is 2.5 N to 3.5 N.
According to claim 1,
The polarizer is a polarizing plate, characterized in that the polyvinyl alcohol-based resin.
According to claim 1,
The polarizing plate, characterized in that the high humidity is 90%.
According to claim 1,
The high temperature is a polarizing plate, characterized in that 60 ℃.
An image display device having the polarizing plate according to any one of claims 1 to 10.

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