Polarizing plate

Abstract

The present application relates to a polarizing plate and a liquid crystal display device. The polarizing plate which is thin and light, meets requirements for physical properties such as durability, moisture resistance, workability and light leakage inhibiting ability, and has an antistatic property, and the liquid crystal display device including the same may be provided.

Claims

1. A polarizing plate, comprising: a polarizer; a pressure-sensitive adhesive layer; and a polyvinyl alcohol adhesive layer disposed between the polarizer and the pressure-sensitive adhesive layer; wherein the pressure-sensitive adhesive layer disposed on at least one surface of the polyvinyl alcohol adhesive layer has different peeling strengths with respect to glass at a first surface that is directly adjacent to the polyvinyl alcohol adhesive layer and a second surface that is an opposite to the first surface, a ratio(P2/P1) of the peeling strength with respect to glass of the second surface(P2) to the peeling strength with respect to glass of the first surface(P1) being 8.33 to 30, and a surface resistance being 2.110.sup.9 /square to 2.710.sup.9 /square, wherein the pressure-sensitive adhesive layer is a layer of a pressure sensitive adhesive composition comprising an acryl polymer and an antistatic agent, wherein the antistatic agent is present in an amount from 0.1 to 2 parts by weight relative to 100 parts by weight of the acryl polymer, wherein the pressure-sensitive adhesive layer has a thickness of 40 m to 60 m, and an average tensile modulus of the pressure-sensitive adhesive layer is 90 to 1,000 MPa at a temperature ranging from 10 C. to 40 C., and a peeling strength at a temperature ranging from 10 C. to 40 C. of the second surface in the pressure-sensitive adhesive layer with respect to glass is 100 to 2,500 gf/25 mm.

2. The polarizing plate of claim 1, wherein the pressure-sensitive adhesive layer has an interpenetrating polymer network(IPN) structure.

3. The polarizing plate of claim 1, wherein the pressure-sensitive adhesive layer has a tensile modulus that varies in a thickness direction.

4. The polarizing plate of claim 1, wherein a peeling strength at a temperature ranging from 10 C. to 40 C. with respect to glass of the first surface that is adjacent to the polarizer in the pressure-sensitive adhesive layer is 5 to 100 gf/25 mm.

5. The polarizing plate of claim 1, wherein the acryl polymer comprises a polymerization unit derived from 70 to 99.9 parts by weight of an alkyl (meth)acrylate, 1 to 14 parts by weight of a compound of Formula 1, and 0.1 to 30 parts by weight of a copolymerizable monomer having a polar group: ##STR00005## where R is hydrogen or an alkyl group, A is an alkylene group or an alkylidene group, R.sub.1 is an alkyl group or an aryl group, and n is a number between 1 and 50.

6. The polarizing plate of claim 5, wherein the copolymerizable monomer having a polar group comprises a polymerization unit derived from 0.1 to 20 parts by weight of a copolymerizable monomer having a hydroxyl group, and 0.5 to 10 parts by weight of a copolymerizable monomer having an acid group.

7. The polarizing plate of claim 1, wherein the antistatic agent is an inorganic salt or organic salt.

8. The polarizing plate of claim 7, wherein the inorganic salt comprises an alkali metal cation or an alkali earth metal cation.

9. The polarizing plate of claim 7, wherein the organic salt comprises an onium cation.

10. The polarizing plate of claim 1, wherein the pressure-sensitive adhesive composition further comprises a multifunctional crosslinking agent.

11. The polarizing plate of claim 1, wherein the pressure-sensitive adhesive composition further comprises an active energy ray-polymerizable compound.

12. The polarizing plate of claim 1, wherein the pressure-sensitive adhesive composition further comprises an ultraviolet (UV) absorbent.

13. The polarizing plate of claim 1, wherein the pressure-sensitive adhesive composition further comprises a compound of Formula 2: ##STR00006## where M.sub.1 to M.sub.5 are each independently R.sup.1N, (R.sup.2)(R.sup.3)C or (R.sup.4)(R.sup.5)C, in which R.sup.1 is a hydrogen atom, an alkyl group or an alkoxy group, R.sup.2 and R.sup.3 are each independently an alkyl group, R.sup.4 and R.sup.5 are each independently a hydrogen atom or an alkyl group, L is an alkylene group or an alkylidene group, and P is an alkyl group or a substituent of Formula 3, and in Formula 2, at least one of M.sub.2 to M.sub.4 is the R.sup.1N, and the M.sub.1, M.sub.2, M.sub.3, M.sub.4 or M.sub.5 immediately adjacent to the at least one of M.sub.2 to M.sub.4 that is the R.sup.1N is the (R.sup.2)(R.sup.3)C: ##STR00007## where M.sub.6 to M.sub.10 are each independently R.sup.1N, (R.sup.2)(R.sup.3)C or (R.sup.4)(R.sup.5)C, and here, R.sup.1 is a hydrogen atom, an alkyl group or an alkoxy group, R.sup.2 and R.sup.3 are each independently an alkyl group, and R.sup.4 and R.sup.5 are each independently a hydrogen atom or an alkyl group, and in Formula 3, at least one of M.sub.7 to M.sub.9 is the R.sup.1N, and the M.sub.6, M.sub.7, M.sub.8, M.sub.9 or M.sub.10 immediately adjacent to the at least one of M.sub.7 to M.sub.9 that is the R.sup.1N is the (R.sup.2)(R.sup.3)C.

14. A liquid crystal display device in which the polarizing plate of claim 1 is attached to one or both sides of a liquid crystal panel by the pressure-sensitive adhesive layer.

15. The liquid crystal display device of claim 14, wherein the liquid crystal panel is a twisted nematic (TN) panel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a cross-sectional view of an exemplary polarizing plate.

(2) FIG. 2 is a diagram illustrating a exemplary process of forming a pressure-sensitive adhesive layer.

(3) FIG. 3 is a cross-sectional view of an exemplary polarizing plate.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

(4) Hereinafter, the present invention will be described in detail with reference to Examples according to the present invention and Comparative Examples not according to the present invention. However, the present invention is not limited to the following Examples.

(5) 1. Evaluation of Elastic Modulus (Average Elastic Modulus)

(6) In this specification, a tensile modulus of a pressure-sensitive adhesive was measured by a stress-strain test due to tension according to a method defined in ASTM D638. When it was difficult to directly measure the tensile modulus, a storage modulus was measured and then converted by the following Conversion Formula. In detail, a stacked structure shown in FIG. 2 (a stacked structure of a PET releasing film(202A), a cured product of a layer(201) of a pressure-sensitive adhesive composition and a PET releasing film(202B)) prepared in Examples and Comparative Examples was cut into a dog bone-type specimen with a size of 7 cm (length)1 cm (width), both ends of the specimen were fixed with jigs for a tensile test, and the tensile modulus was measured. The conditions for measuring the tensile modulus were as follows.

(7) <Conditions for Measuring Tensile Modulus>

(8) Measuring Apparatus: Universal Test Machine (UTM)

(9) Equipment Model: Zwick Roell Z010, Instron

(10) Measurement Conditions:

(11) Load Cell: 500 N

(12) Tensile Rate: 3 mm/sec

(13) <Measurement of Storage Modulus and Conversion into Tensile Modulus>

(14) A pressure-sensitive adhesive was cut into a size of 15 cm25 cm25 m (widthlengththickness) and then stacked in five layers. Subsequently, the stacked adhesives were cut into a circle having a diameter of 8 mm, and pressed using glass overnight to enhance wettability at an interface between the layers, thereby removing air bubbles generated during stacking. As a result, a specimen was prepared. Subsequently, the specimen was placed on a parallel plate, and a gap was adjusted. Then, after Normal & Torque was adjusted to zero, and the stabilization of normal force was checked, the storage modulus was measured under the following conditions, and the tensile modulus was calculated according to the following Conversion Formula.

(15) Measurement Apparatus and Measurement Conditions

(16) Measurement Apparatus: ARES-RDA, TA Instruments Inc. with forced convection oven

(17) Measurement Conditions:

(18) Geometry: 8 mm parallel plate

(19) Gap: approximately 1 mm

(20) Test Type: dynamic strain frequency sweep

(21) Strain=10.0 [%], temperature: 30 C.

(22) Initial Frequency: 0.4 rad/s, final frequency: 100 rad/s

(23) <Conversion Formula>
E=3G

(24) In the above Formula, E is a tensile modulus, and G is a storage modulus.

(25) 2. Evaluation of Peeling Strength and Repeelability

(26) A polarizing plate was formed by the method described in Example 1 using a pressure-sensitive adhesive formed according to each of Examples and Comparative Examples, except that a direction of the pressure-sensitive adhesive was changed in a direction along a surface of the pressure-sensitive adhesive whose peeling strength was to be measured. That is, in the formation of the polarizing plate disclosed in Example 1, when the peeling strength of a second surface was measured, a first surface was attached to the polarizer, and when the peeling strength of the first surface was measured, the second surface was attached to the polarizer. Afterward, a specimen was formed by cutting the polarizing plate into a size of 25 mm100 mm (widthlength). Subsequently, a PET releasing film attached to the pressure-sensitive adhesive was peeled off, and the surface of the pressure-sensitive adhesive was attached to alkali-free glass using a 2 kg roller according to JIS Z 0237. Subsequently, the alkali-free glass to which the pressure-sensitive adhesive was attached was compressed in an autoclave (50 C., 0.5 atm) for about 20 minutes, and stored under conditions of constant temperature and constant humidity (23 C., relative humidity: 50%) for 25 hours. Then, using a texture analyzer (TA) (Stable Micro System (United Kingdom)), the polarizing plate was peeled off of the alkali-free glass at a peeling rate of 300 mm/min and a peeling angle of 180 degree to measure a peeling strength. In addition, repeelability was evaluated under the following criteria:

(27) <Criteria for Evaluation of Repeelability>

(28) : A day after attachment, the peeling strength was 800N/25 mm or less.

(29) : A day after attachment, the peeling strength was 1,000N/25 mm or more.

(30) x: A day after attachment, the peeling strength was 2,000N/25 mm or more.

(31) 3. Evaluation of Haze

(32) A film-shape specimen (thickness of pressure-sensitive adhesive layer: 23 m) was formed using a pressure-sensitive adhesive composition of Examples and Comparative Examples, and haze of the pressure-sensitive adhesive layer was measured using a haze meter (HR-100, Murakami Color Research Laboratory, Japan) according to JIS K 7105-1.

(33) 4. Evaluation of Durability

(34) Two layers of specimens were prepared by cutting a polarizing plate formed in Examples and Comparative Examples into a size of 90 mm170 mm (widthlength). Subsequently, the prepared two layers of specimens were attached to both surfaces of a glass substrate (110 mm190 mm0.7 mm=widthlengththickness) such that optical absorption axes of each polarizing plate crossed, thereby preparing a sample. A pressure applied during attachment was about 5 kg/cm.sup.2, and the preparation of the sample was carried out in a clean room to avoid generation of air bubbles or impurities at an interface. Afterward, the humidity and thermal resistance of the sample was evaluated by observing whether air bubbles or peeling occurred at a pressure-sensitive adhesive interface after the sample was left for 1,000 hours under conditions including a temperature of 60 C. and a relative humidity of 90%, and the thermal resistance was evaluated by observing whether air bubbles formed or peeling occurred at the pressure-sensitive adhesive interface after the sample was left for 1,000 hours at a temperature of 80 C. The prepared samples were left at room temperature for 24 hours right before the evaluation of the humidity and thermal resistance or thermal resistance and durability. Evaluation conditions are as follows:

(35) <Criteria for Evaluation of Durability>

(36) : No air bubbles and/or peeling

(37) : Minor air bubbles and/or peeling

(38) : Moderate air bubbles and/or peeling

(39) x: Considerable air bubbles and/or peeling

(40) 5. Evaluation of Water Resistance

(41) A sample was prepared by attaching specimens formed by cutting a polarizing plate formed in Examples and Comparative Examples into a size of 90 mm170 mm (widthlength) to one surface of a glass substrate (110 mm190 mm0.7 mm=widthlengththickness). A pressure applied during attachment was approximately 5 kg/cm.sup.2, and the preparation of the sample was carried out in a clean room to avoid generation of air bubbles or impurities at an interface. Subsequently, the prepared sample was put into water at a temperature of 60 C. and left for 24 hours to observe whether air bubbles formed or peeling occurred. The water resistance was evaluated according to the following criteria.

(42) <Criteria for Evaluation of Water Resistance>

(43) : No air bubbles and/or peeling

(44) : Some air bubbles and/or peeling

(45) x: Considerable air bubbles and/or peeling

(46) 6. Evaluation of Uniformity of Light Transmission

(47) A polarizing plate formed in Examples and Comparative Examples was attached to both surfaces of a 22 inch LCD monitor (LG Philips LCD) in a state in which optical axes crossed each other, stored under conditions of constant temperature and constant humidity (23 C., relative humidity: 50%) for 24 hours, and left at 80 C. for 200 hours. Subsequently, light was radiated onto the monitor using a backlight in a dark room, and the uniformity of light transmission was evaluated according to the following criteria:

(48) <Criteria for Evaluation of Uniformity of Light Transmission>

(49) : no non-uniformity observed in four corners of monitor with naked eye

(50) : some non-uniformity observed in four corners of monitor with naked eye

(51) x: considerable non-uniformity observed in four corners of monitor with naked eye

(52) 7. Evaluation of Weight Average Molecular Weight and Distribution of Molecular Weight

(53) The weight average molecular weight and the distribution of a molecular weight of an acrylic polymer were measured using GPC under the following conditions. To plot a calibration curve, measurement results were converted using standard polystyrene of an Agilent system.

(54) <Conditions for Measuring Weight Average Molecular Weight>

(55) Measuring Apparatus: Agilent GPC (Agilent 1200 series, USA)

(56) Column: Two connected PL mixed B

(57) Column Temperature: 40 C.

(58) Eluent: Tetrahydrofuran

(59) Flow Rate: 10 mL/min

(60) Concentration: 2 mg/mL (100 L injection)

(61) 8. Measurement of Surface Resistance

(62) A specimen was prepared by cutting a polarizing plate having a pressure-sensitive adhesive layer to have a size of 50 mm50 mm (widthlength), and a surface resistance of the pressure-sensitive adhesive layer was measured according to the manufacturer's manual using MCP-HT 450 equipment (Mitsubishi Chemical, Japan) after a releasing PET attached to the pressure-sensitive adhesive layer of the specimen was removed.

PREPARATION EXAMPLE 1

Preparation of Acrylic Polymer (A)

(63) 90 parts by weight of n-butyl acrylate (n-BA), 12 parts by weight of methoxy ethyleneglycol acrylate (MEA) and 2 parts by weight of 2-hydroxyethyl acrylate (2-HEA) were put into a 1 L reaction vessel equipped with a cooling device to reflux a nitrogen gas and facilitate temperature control. Subsequently, 180 parts by weight of ethyl acetate (EAc) was put as a solvent into the reaction vessel and purged with the nitrogen gas for 60 minutes to remove oxygen. Afterward, the temperature was maintained at 60 C., 0.05 parts by weight of azobisisobutyronitrile (AIBN) was put as a reaction initiator into the reaction vessel, and the reaction was carried out for 8 hours. After the reaction, the reaction product was diluted with ethyl acetate (EAc), and thus an acrylic polymer (A) having a solid content of 30 wt %, a weight average molecular weight of 1,000,000, and a molecular weight distribution of 4.9 was prepared.

PREPARATION EXAMPLE 2

Preparation of Acrylic Polymer (B)

(64) An acrylic polymer was prepared by the same method as described in Preparation Example 1, except that 90 parts by weight of n-butyl acrylate (n-BA), 13 parts by weight of methoxy ethyleneglycol acrylate (MEA), 2 parts by weight of 2-hydroxyethyl acrylate (2-HEA), and 0.5 parts by weight of acrylic acid (AA) were put into the reaction vessel.

PREPARATION EXAMPLE 3

Preparation of Acrylic Polymer (C)

(65) An acrylic polymer was prepared by the same method as described in Preparation Example 1, except that 90 parts by weight of n-butyl acrylate (n-BA), 15 parts by weight of methoxy ethyleneglycol acrylate (MEA), and 2 parts by weight of 2-hydroxyethyl acrylate (2-HEA) were put into the reaction vessel.

EXAMPLE 1

Preparation of Pressure-Sensitive Adhesive

(66) A pressure-sensitive adhesive composition was prepared by blending 100 parts by weight of the acrylic polymer prepared in Preparation Example 1, 3 parts by weight of a multifunctional crosslinking agent (TDI-based isocyanate, Coronate L, Nippon Polyurethane Industry (Japan)), 100 parts by weight of a multifunctional acrylate (trifunctional urethane acrylate, Aronix M-315, Toa Gosei K.K.), 3 parts by weight of hydroxycyclohexylphenylketone as a photoinitiator (Irgacure 184, Ciba Specialty Chemicals (Switzerland)), 3 parts by weight of a triazine-based UV absorbent (Tinuvin 400, Ciba Specialty Chemicals (Switzerland)), 2 parts by weight of lithium bistrifluorosulfonylimide as an antistatic agent, and 0.1 parts by weight of a silane coupling agent having a -cyanoacetyl group (M812, LG Chem (Korea)) in a solvent to have a solid content of 30 wt %. Subsequently, the prepared pressure-sensitive adhesive composition was coated on a releasing-treated surface of a PET film (thickness: 38 m, MRF-38, Mitsubishi) subjected to releasing treatment to have a predetermined thickness, and the resulting film was dried in an oven at 110 C. for 3 minutes. Then, a stacked structure such as that shown in FIG. 2 was formed by further laminating a releasing-treated surface of the releasing-treated PET film (thickness: 38 m, MRF-38, Mitsubishi) on the dried coating layer, and irradiated by UV rays (Luminance: 250 mW/cm.sup.2, Intensity of Light: 300 mJ/cm.sup.2) using a high pressure mercury lamp, thereby forming a pressure-sensitive adhesive layer (a cured layer of the layer(201) of the pressure-sensitive adhesive composition) between two of the PET releasing films(202A, 202B). Hereinafter, for convenience of description, a surface of the pressure-sensitive adhesive layer irradiated by UV rays is called a second surface(201a), and the opposite surface is called a first surface(201b).

(67) <Conditions for UV Radiation>

(68) Luminance: 250 mW/cm.sup.2

(69) Intensity of UV radiation: 300 mJ/cm.sup.2

(70) Formation of Polarizing Plate

(71) A polarizer was formed by extending a polyvinylalcohol-based resin film, dying the film with iodine, and treating the film with an aqueous boric acid solution. Subsequently, a 60 m thick triacetyl cellulose (TAC) film was attached to one surface of the polarizer using a water-based polyvinylalcohol-based adhesive conventionally used to attach a protective film to a polarizer. Afterward, the second surface of the prepared pressure-sensitive adhesive was laminated on a surface of the polyvinylalcohol-based polarizer to which the TAC film was not attached using the same water-based polyvinylalcohol-based adhesive as used above, thereby forming a polarizing plate.

EXAMPLES 2 to 4 and COMPARATIVE EXAMPLES 1 and 4

(72) A polarization plate was formed by the same method as described in Example 1, except that components of the pressure-sensitive adhesive composition were changed as shown in Table 1.

(73) TABLE-US-00001 TABLE 1 Example Comparative Example 1 2 3 4 5 1 2 3 4 5 Acrylic A 100 100 100 100 100 100 100 100 polymer B 100 C 100 Crosslinking 3 3 3 3 3 3 3 3 3 3 agent MFA 100 120 150 120 120 120 120 120 100 Photoinitiator 3 3 3 3 3 3 3 3 3 UV absorbent 3 2 3 3 3 0.1 10 3 3 Silane coupling 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 agent LiTFSi 2 2 2 2 2 2 2 2 Thickness (m) 40 40 40 60 60 40 40 15 40 40 content units: parts by weight MFA: trifunctional urethane acrylate (Aronix M-315, Toa Gosei K.K.) Crosslinking agent: TDI-based isocyanate crosslinking agent (Coronate L, Nippon Polyurethane) Photoinitiator: Irg184: hydroxyl cyclohexylphenyl ketone (Swiss Ciba specialty Chemical) UV absorbent: triazine-based UV absorbent (Tinuvin 400, Swiss Ciba specialty Chemical) Silane coupling agent: M812: beta-cyanoacetyl group-containing silane coupling agent (LG Chemical, Korea) LiTFSi: lithium bistrifluorosulfonylimide

(74) Measurement results for Examples and Comparative Examples are summarized in Table 2.

(75) TABLE-US-00002 TABLE 2 Example Comparative Example 1 2 3 4 5 1 2 3 4 5 Tensile modulus 90 150 200 120 120 300 50 140 0.1 85 (RT, MPa) Peeling strength 60 30 15 40 35 15 350 20 500 110 (second surface) (gf/25 mm) Peeling strength 500 350 450 650 640 60 600 70 800 400 (first surface) (gf/25 mm) Surface resistance 2.5 2.1 2.7 2.3 2.3 2.8 2.7 More More 2.5 (X 10.sup.9 / ) than than 100 100 Repeelability Thermal X X X X resistance and durability Humidity X X X resistance and durability Moisture X X X resistance Uniformity of X light transmittance *RT: room temperature

(76) A thin and lightweight polarizing plate that meets requirements for physical properties such as durability, moisture resistance, workability and light leakage inhibiting ability, and has an antistatic property, and a liquid crystal display device including the same, can be provided.

(77) While the invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention as defined by the appended claims.