Polarizing plate, liquid crystal panel and display device

Abstract

The present invention relates to a polarizing plate including: a polarizer; a hard coating layer having a thickness of 10 μm or less formed on one surface side of the polarizer; and an optical laminate including a light-transmitting substrate formed on the other surface side of the polarizer.

Claims

1. A polarizing plate comprising: a polarizer; a hard coating layer having a thickness of 10 μm or less formed on one surface side of the polarizer; and an optical laminate including a light-transmitting substrate formed on the other surface side of the polarizer, wherein the hard coating layer contacts the polarizer, and wherein a ratio of a second heat shrinkage deformation value in a second direction of the optical laminate to a first heat shrinkage deformation value in a first direction of the optical laminate is 0.8 to 1.2 and wherein the first direction is perpendicular to the second direction, and wherein each of the first heat shrinkage deformation value and the second heat shrinkage deformation value is a difference between an initial length of each of the first direction and the second direction of the optical laminate and a length value as measured after exposure of the optical laminate to a condition of a temperature of 100° C. to 120° C. for 80 to 120 hours.

2. The polarizing plate of claim 1, wherein the first direction of the optical laminate is a machine direction of the light-transmitting substrate, and the second direction of the optical laminate is a transverse direction of the light-transmitting substrate.

3. The polarizing plate of claim 1, wherein the light-transmitting substrate has a thickness direction retardation (Rth) of 3,000 nm or more as measured at a wavelength of 400 nm to 800 nm.

4. The polarizing plate of claim 1, wherein the light-transmitting substrate has a moisture permeation amount of 100 g/m.sup.2 or less as measured for 24 hours under a condition of 40° C. and 100% humidity.

5. The polarizing plate of claim 1, wherein a ratio of the thickness of the hard coating layer to the thickness of the light-transmitting substrate is 0.02 to 0.25.

6. The polarizing plate of claim 1, wherein the thickness of the polarizer plus the hard coating layer plus the light-transmitting substrate is 200 μm or less.

7. The polarizing plate of claim 1, wherein the hard coating layer includes a binder resin and organic or inorganic fine particles dispersed in the binder resin, the organic fine particles having a particle size of 0.5 μm to 10 μm, and the inorganic fine particles having a particle size of 1 nm to 500 nm.

8. The polarizing plate of claim 1, further comprising a second hard coating layer having a thickness of 1 to 100 μm formed on one surface of the light-transmitting substrate opposite side against the polarizer.

9. The polarizing plate of claim 8, further comprising a low-refractive index layer having a refractive index of 1.20 to 1.60 in the wavelength range of 380 nm to 780 nm formed on the other surface of the second hard coating layer.

10. The polarizing plate of claim 1, further comprising an adhesive layer disposed between the polarizer and the light-transmitting substrate and having a thickness of 0.1 μm to 5 μm.

11. A liquid crystal panel comprising a liquid crystal cell and the polarizing plate of claim 1 formed on at least one surface of the liquid crystal cell.

12. The liquid crystal panel of claim 11, wherein the liquid crystal panel comprises two polarizing plates such that each of the two polarizing plates is formed on each of two surfaces of the liquid crystal cell, and the two polarizing plates are positioned such that a MD direction of the polarizer of the polarizing plate formed on one surface side of the liquid crystal cell and a MD direction of the polarizer of the polarizing plate formed on the other surface are perpendicular to each other.

13. A display device comprising the polarizing plate of claim 1.

14. The polarizing plate of claim 1, wherein the first direction of the optical laminate is a machine direction of the light-transmitting substrate, and the second direction of the optical laminate is a transverse direction of the light-transmitting substrate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows an example of a polarizing plate of an embodiment of the present invention.

(2) FIG. 2 shows another example of a polarizing plate of an embodiment of the present invention.

(3) FIG. 3 shows yet another example of a polarizing plate of an embodiment of the present invention

(4) FIG. 4 shows an example of a liquid crystal panel of an embodiment of the present invention.

(5) FIG. 5 shows another example of a liquid crystal panel of an embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(6) Hereinafter, embodiments of the present invention are described in further detail with reference to examples. However, these examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

Preparation Example

Preparation Example 1: Preparation of Optical Laminate

(7) (1) Preparation of Coating Liquid for Forming a Hard Coating Layer

(8) The components shown in Table 1 were mixed to prepare a coating liquid (B1, B2) for forming a hard coating layer of the optical laminate.

(9) TABLE-US-00001 TABLE 1 (unit: g) B1 B2 TMPTA — 10.35 PETA 14.31 4.56 UA-306T 4.07 4.56 SC2152 7.58 7.25 IRG-184 1 1.26 Tego wet 270 0.05 0.05 BYK 350 0.05 0.05 2-butanol 25.87 30.31 IPA 45.82 40.41 XX-103BQ(2.0 μm, RI 0.35 0.38 1.515) XX-113BQ(2.0 μm, RI 0.7 0.61 1.555) MA-ST(30% in MeOH) 0.2 0.21 TMPTA: trimethylolpropane triacrylate) PETA: pentaerythritol triacrylate UA-306T: urethane acrylate series, reaction product of toluene diisocyanate and pentaerythritol triacrylate (manufacture by Kyoeisha Chemical) SC2152: Compound in which hexamethylene diisocyanurate (HMDI) and acrylate compound are connected by urethane bond [mass average molecular weight: 20,000/manufacturer: Miwon Specialty Chemical] IRG-184: initiator (Irgacure 184, Ciba Specialty Chemicals) Tego wet 270: leveling agent (Tego) BYK 350: leveling agent (BYK-Chemie) 2-butanol: butyl alcohol IPA: isopropyl alcohol XX-103BQ (2.0 μm, Refractive Index 1.515): copolymerized particles of polystyrene and polymethylmethacrylate (manufactured by Sekisui Plastic) XX-113BQ(2.0 μm, Refractive Index 1.555): copolymerized particles of polystyrene and polymethylmethacrylate (manufactured by Sekisui Plastic) MA-ST (30% in MeOH): Dispersion in which silica nanoparticles with a size of 10 to 15 nm are dispersed in methyl alcohol (manufactured by Nissan Chemical)

(10) (2) Preparation of Coating Liquid (C) for Forming Low-Refractive Index Layer

(11) 100 g of trimethylolpropane triacrylate (TMPTA), 283 g of hollow silica nanoparticles (diameter range: about 42 nm to 66 nm, JSC Catalyst and Chemicals), 59 g of solid silica nanoparticles (diameter range: about 12 nm to 19 nm), 115 g of a first fluorine-containing compound (X-71-1203M, Shin-Etsu), 15.5 g of a second fluorine-containing compound (RS-537, DIC Corporation) and 10 g of an initiator (Irgacure 127, Ciba) were diluted in a MIBK (methyl isobutyl ketone) solvent so as to have a solid content of 3 wt %, thereby preparing a coating liquid for forming a low-Refractive Index layer.

(12) (3) Preparation of an Optical Laminate with a Hard Coat Layer Formed on a Light-Transmitting Substrate

(13) 1) Measurement of the Ratio of Heat Shrinkage Rate

(14) The ratio of a heat shrinkage rate in the MD direction: a heat shrinkage rate in the TD direction of the polyethylene terephthalate (PET) film used in each of Examples and Comparative Examples was calculated by cutting each PET film into a size of 10 cm*10 cm (width*length), allowing to stand at 80° C. for 30 minutes and then determining the heat shrinkage rate (deformed length/initial length) in each of the MD and TD directions.

(15) PET 1: The ratio of heat shrinkage rate (MD:TD) is about 1

(16) PET 2: The ratio of heat shrinkage rate (MD:TD) is about 0.5

(17) 2) Preparation of Optical Laminate

(18) Each of the prepared coating liquids for forming a hard coating layer (B1, B2) was coated onto the respective polyethylene terephthalate (PET) films shown in Tables 2 and 3 below using a #12 Mayer bar, and then dried at the temperature shown in Tables 2 and 3 below for 2 minutes, and UV-cured to form a hard coating layer (coating thickness of 5 μm). The H bulb was used as a UV lamp and a curing reaction was performed under nitrogen atmosphere. The amount of UV light irradiated upon curing was 150 mJ/cm.sup.2.

(19) The coating liquid (C) for forming the low-refractive index layer was coated onto the hard coating film using a #4 Mayer bar so that the thickness was about 110 to 120 nm, and then dried and cured for 1 minute at the temperature shown in Tables 2 and 3 below. During the curing, the dried coating was irradiated with ultraviolet light of 252 mJ/cm.sup.2 under a nitrogen purge.

(20) 3) Measurement of the Heat Shrinkage Deformation Value of the Optical Laminate

(21) The optical laminate was cut into a size of 12 cm in the MD direction and the TD direction of the polyethylene terephthalate (PET) film, respectively, to prepare a sample for heat shrinkage deformation value measurement.

(22) The prepared sample was allowed to stand at a temperature of 100° C. for 96 hours, and then the length of each of the MD direction and the TD direction was determined, thereby measuring the heat shrinkage deformation value in each direction.
Heat shrinkage deformation value in the first direction of the optical laminate (MD direction of PET)=The initial length of the first direction of the optical laminate (MD direction of PET)−The length of the first direction of the optical laminate (MD direction of PET) measured after exposure at a temperature of 100° C. for 96 hours  [General Formula 2-1]
Heat shrinkage deformation in the second direction of the optical laminate (TD direction of PET)=The initial length of the second direction of the optical laminate (TD direction of PET)−The length of the second direction of the optical laminate (TD direction of PET) measured after exposure at a temperature of 100° C. for 96 hours  [General Formula 3-1]

(23) Then, in the optical laminate, the ratio (R) of a heat shrinkage deformation value in the second direction of the optical laminate (TD direction of PET) to a heat shrinkage deformation value in the first direction of the optical laminate (MD direction of PET) was determined.
Ratio (R)=Heat shrinkage deformation value in the second direction of the optical laminate (TD direction of PET)/Heat shrinkage deformation value in the first direction of the optical laminate (MD direction of PET)  [General Formula 1-1]

Preparation Example 2

Preparation of Coating Liquid for Forming Hard Coating Layer and Preparation of Polarizer with Hard Coating Layer Formed Thereon

(24) (1) Preparation of Coating Liquid (A) for Forming Hard Coating Layer

(25) 28 g of trimethylolpropane triacrylate, 2 g of KBE-403, 0.1 g of initiator KIP-100f, and 0.06 g of leveling agent (Tego wet 270) were uniformly mixed to prepare a hard coating composition.

Examples and Comparative Examples

Preparation of Polarizing Plate and Liquid Crystal Panel

(26) (1) Preparation of Polarizing Plate

(27) Polyvinyl alcohol polarizer (thickness: 25 um, manufacturer: LG Chem) was bonded onto the light-transmitting substrate of the optical laminate prepared in Preparation Example 1 using a UV adhesive, then the prepared coating liquid (A) for forming the hard coating layer was coated onto the opposite side of the light-transmitting substrate to a thickness of 7 um, and the dried coating was irradiated with ultraviolet light of 500 mJ/cm.sup.2 under nitrogen purge to form a hard coating layer.

(28) (2) Preparation of Sample for Thermal Shock Evaluation

(29) The polarizing plate cut into a square where the length of one side was 10 cm was bonded to one surface of the glass for TV (12 cm wide, 12 cm long, and 0.7 mm thick) to prepare a sample for thermal shock evaluation. At this time, the polarizing plate was cut so that the MD direction of the polarizer was parallel to one side of the square.

Experimental Example

Thermal Shock Evaluation

(30) The prepared polarizing plate and a sample for evaluation to which the polarizing plate was bonded, were subjected to a thermal shock test under the following conditions, and the following three items were measured and confirmed.

(31) Measuring Conditions:

(32) The polarizing plate and the sample for thermal shock evaluation were placed upright on a thermal shock chamber. The process in which the temperature was raised from room temperature to 80° C. and left for 30 minutes, after which the temperature was lowered to −30° C. and left for 30 minutes, and then the temperature was controlled to room temperature was defined as 1 cycle, and a total of 100 cycles were repeated.

(33) (1) Number of Occurrence of Cracks

(34) The cracks occurred between the polarizers of the sample for evaluation and the gaps formed between the polarizing plates were confirmed with the naked eye, and the number of occurrence of cracks with a length of 1 cm was confirmed.

(35) (2) Bubble

(36) The bubbles occurred between the polarizer and the protective film of the sample for evaluation and the bubbles occurred between the polarizer and the hard coating layer were confirmed with the naked eye and the number of bubbles having a diameter of 5 mm or more was confirmed.

(37) (3) Vertex Detachment (mm), 10×10/Film

(38) The four vertices of the polarizing plate sample were observed, and the detachment between the coating layer and the polarizer, the peeling between the polarizer and the protective film, and the peeling and bending between the hard coating and the cohesive layer were observed. When the detachment occurred and bending appeared, the bending height from the floor in a state where the sample placed flat on the floor was measured to calculate the average height.

(39) TABLE-US-00002 TABLE 2 Example 1 Example 2 Example 3 Anti-reflection Low-refractive index layer — Coating Coating film liquid (C) liquid (C) Drying temperature of low-refractive — 40° C. 40° C. index layer Hard coating layer B1 B1 B2 Thickness of hard coating layer 3.8 μm 4.0 μm 5.2 μm Drying temperature of hard coating 60° C. 60° C. 60° C. Substrate PET 1 PET 1 PET 1 Optical laminate Heat shrinkage deformation value in 0.73 mm 0.63 mm 0.67 mm MD direction of PET (1) Heat shrinkage deformation value in  0.7 mm 0.58 mm 0.58 mm TD direction of PET (2) Ratio(R)(2/1) 0.958904 0.920635 0.865672 Result of thermal Number of occurrence of cracks 0 0 0 shock evaluation Bubble 0 0 0 (10 × 10) Vertex detachment (mm), 10 × 10/film 0 0 0

(40) TABLE-US-00003 TABLE 3 Comparative Comparative Comparative Comparative Example 1 Example 2 Example 3 Example 4 Anti-reflection Low-refractive index — Coating liquid Coating liquid — film layer (C) (C) Drying temperature — 40° C. 40° C. — of low-refractive index layer Hard coating layer B1 B1 B2 B2 Thickness of hard 4.0 μm 4.3 μm 5.3 μm 5.0 μm coating layer Drying temperature 60° C. 60° C. 60° C. 60° C. of hard coating Substrate PET 2 PET 2 PET 2 PET 2 Optical laminate Heat shrinkage 0.21 mm 0.21 mm 0.42 mm 0.41 mm deformation value in MD direction of PET (1) Heat shrinkage  0.5 mm 0.53 mm 0.67 mm 0.58 mm deformation value in TD direction of PET (2) Ratio (R)(2/1) 2.380952 2.52381 1.595238 1.414634 Result of Number of 0 1 2 2 thermal shock occurrence of cracks evaluation Bubble 1 1 2 2 (10 × 10) Vertex detachment 4 3 4 4 (mm), 10 × 10/film

(41) As shown in Table 2 and Table 3 above, it was confirmed that in the polarizing plate of Examples, even when a temperature of 60° C. or higher is applied in the production process, the heat shrinkage rate and the heat shrinkage deformation value between detail layers is controlled, in particular, the ratio of a heat shrinkage deformation value in the second direction of the optical laminate perpendicular to the first direction to a heat shrinkage deformation value in the first direction of the optical laminate is within 0.8 to 1.2. Consequently, it was confirmed that the polarizing plates of Examples have excellent bending balance, and prevent the occurrent of cracks in the polarizing plate, and further can prevent a light leakage phenomenon of the liquid crystal display device.

EXPLANATION OF SIGN

(42) 10: light-transmitting substrate 20: polarizer 30: hard coating layer 40: anti-reflection layer 50: adhesive layer 60: cohesive layer 70 liquid crystal cell 100 polarizing plate 200 liquid crystal panel