Polarizing plate having pressure sensitive adhesive layer with improved light leakage property
The present invention relates to a polarizing plate characterized in that pressures-sensitive adhesives used in the upper and lower polarizing plates have different elastic properties and a liquid crystal display device comprising the same. More specifically, the present invention relates to a polarizing plate with improved light leakage phenomenon in accordance with bend of liquid crystal panels, characterized in that as slid distances of pressure-sensitive adhesives on the polarizing plate having the pressure-sensitive adhesive layer formed thereon and bonded to a glass plate with a contact area of 1 cm×1 cm at the time of applying a load of 1,000 gf at room temperature (25° C.) for 1,000 seconds, the difference between the slid distance X 1 of pressure-sensitive adhesive for the upper polarizing plate and the slid distance X 2 of pressure-sensitive adhesive for the lower polarizing plate is 50 to 500 μm.
1. A liquid crystal display device comprising:
a liquid crystal panel that comprises an upper polarizing plate that is attached on one side of a liquid crystal cell by a pressure-sensitive adhesive layer for the upper polarizing plate and a lower polarizing plate that is attached on the other side of the liquid crystal cell by a pressure-sensitive adhesive layer for the lower polarizing plate, and
a backlight unit which is disposed under the liquid crystal panel which transmits light through the lower polarizing plate that is observed through the upper polarizing plate,
wherein the upper and lower polarizing plates are adhered with crossing their optical axes of 0 degree and 90 degree so that elongation axis directions of the upper and lower polarizing plates are asymmetrical, and
wherein the pressure-sensitive adhesive layers for the upper and the lower polarizing plates comply with Equation 1 and Equation 2 below:
Δ X=X 1 −X 2 =162 μm to 279 μm (1)
X 1 and X 2 =233 μm to 720 μm (2)
wherein,
X 1 is a slid distance measured with respect to the pressure-sensitive adhesive layer for the upper polarizing plate after adhering the pressure-sensitive adhesive layer to a glass plate so as to have a contact area of 1 cm×1 cm and then applying a load of 1,000 gf at room temperature (25° C.) for 1,000 seconds,
X 2 is a slid distance measured with respect to the pressure-sensitive adhesive layer for the lower polarizing plate after adhering the pressure-sensitive adhesive layer to a glass plate so as to have a contact area of 1 cm×1 cm and then applying a load of 1,000 gf at room temperature (25° C.) for 1,000 seconds, and
ΔX=X 1 −X 2 is a difference between the slid distance measured with respect to the pressure-sensitive adhesive layer for the upper polarizing plate and the slid distance measured with respect to the pressure-sensitive adhesive layer for the lower polarizing plate.
2. The liquid crystal display of claim 1 , wherein the pressure-sensitive adhesive layers for the upper and the lower polarizing plates are formed by acrylic, silicone, rubber, urethane, polyester, or epoxy based pressure-sensitive adhesive composition.
3. The liquid crystal display of claim 1 , wherein the pressure-sensitive adhesive layers for the upper and the lower polarizing plates are formed by an acrylic pressure-sensitive adhesive composition that comprises acrylic copolymer that contains:
i) 90 to 99.9 parts by weight of (meth)acrylic acid ester monomer having an alkyl group of 1 to 4 carbon atoms; and
ii) 0.1 to 10 parts by weight of vinyl monomer and/or acrylic monomer having a cross-linkable functional group.
4. The liquid crystal display device of claim 3 , wherein the (meth)acrylic acid ester monomer having an alkyl group of 1 to 4 carbon atoms is one or more selected from the group consisting of methyl(meth)acrylate, ethyl(meth)acrylate, n-propyl(meth)acrylate, isopropyl(meth)acrylate, n-butyl(meth)acrylate, t-butyl(meth)acrylate, and sec-butyl(meth)acrylate.
5. The liquid crystal display device of claim 3 , wherein the vinyl monomer and/or acrylic monomer having a cross-linkable functional group is one or more selected from the group consisting of 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxylhexyl(meth)acrylate, 2-hydroxyethyleneglycol (meth)acrylate, 2-hydroxypropyleneglycol (meth)acrylate, (meth)acrylic acid, acrylic acid dimer, itaconic acid, maleic acid, maleic anhydride, fumaric acid, acryl amide, N-vinyl pyrrolidone, and N-vinyl carprolactam.
6. The liquid crystal display device of claim 3 , wherein the acrylic copolymer further comprises vinyl monomer of Formula 1:
wherein,
R 4 represents hydrogen or alkyl,
R 3 represents cyano, phenyl unsubstituted or substituted with alkyl, acetyloxy, or COR 5 , where R 5 represents amino or glycidyloxy unsubstituted or substituted with alkyl.
7. The liquid crystal display device of claim 3 , wherein said acrylic pressure-sensitive adhesive composition further comprises 0.1 to 10 parts by weight of a cross-linking agent based on 100 parts by weight of acrylic copolymer.
8. The liquid crystal display device of claim 7 , wherein said cross-linking agent is one or more selected from the group consisting of isocyanate compounds, epoxy compounds, aziridine compounds, and metal chelate compounds.
9. The liquid crystal display device of claim 3 , wherein the acrylic pressure-sensitive adhesive composition has a cross-linking density of 5 to 95%.
10. The liquid crystal display device of claim 1 , further comprising one or more layers selected from the group consisting of a protective layer, a reflective layer, a phase retardation plate, a compensation film for wide view angle and a brightness enhancing film.