Cover window and flexible display device having the same

A cover window, comprising:

• a first layer having a first modulus;
• a second layer disposed on the first layer and having a second modulus smaller than the first modulus;
• and
• a third layer disposed on the second layer and having a third modulus equal to or larger than the first modulus,
• wherein the third layer includes a nanoparticle-polyurethane complex in which polyurethane is bonded with nanoparticles by a covalent bond, and
• wherein the first layer includes a first polyurethane having a weight average molecular weight of 65000 g/mol to 85000 g/mol, the second layer includes a second polyurethane having a weight average molecular weight of 90000 g/mol to 120000 g/mol, and the third layer includes a third polyurethane having a weight average molecular weight of 30000 g/mol to 60000 g/mol,
• wherein the first modulus, the second modulus, and the third modulus refers to a Young's modulus.

A cover window, comprising:

• a first layer having a first modulus;
• a second layer disposed on the first layer and having a second modulus smaller than the first modulus;
• and
• a third layer disposed on the second layer and having a third modulus equal to or larger than the first modulus,
• wherein the third layer includes a nanoparticle-polyurethane complex in which polyurethane is bonded with nanoparticles by a covalent bond, and
• wherein the nanoparticle is silica sol or silica with a surface modified with a hydroxyl group,
• wherein the first modulus, the second modulus, and the third modulus refers to a Young's modulus.

A flexible display device, comprising:

• a display panel;
• and
• a cover window disposed on the display panel, the cover window including a first layer disposed on one surface of the display panel and having a first modulus, a second layer disposed on the first layer and having a second modulus smaller than the first modulus, and a third layer disposed on the second layer and having a third modulus equal to or larger than the first modulus,
• wherein the third layer includes a nanoparticle-polyurethane complex in which polyurethane is bonded with nanoparticles by a covalent bond,
• wherein the first modulus, the second modulus, and the third modulus refers to a Young's modulus.

A flexible display device, comprising:

• a display panel;
• and
• a cover window disposed on the display panel, the cover window including a first layer disposed on one surface of the display panel and having a first modulus, a second layer disposed on the first layer and having a second modulus smaller than the first modulus, and a third layer disposed on the second layer and having a third modulus equal to or larger than the first modulus,
• wherein the third layer includes a nanoparticle-polyurethane complex in which polyurethane is bonded with nanoparticles by a covalent bond, and
• wherein the nanoparticle is silica sol or silica with a surface modified with a hydroxyl group,
• wherein the first modulus, the second modulus, and the third modulus refers to a Young's modulus.

A flexible display device, comprising:

• a display panel;
• and
• a cover window disposed on the display panel, the cover window including a first layer disposed on one surface of the display panel and having a first modulus, a second layer disposed on the first layer and having a second modulus smaller than the first modulus, and a third layer disposed on the second layer and having a third modulus equal to or larger than the first modulus,
• wherein the third layer includes a nanoparticle-polyurethane complex in which polyurethane is bonded with nanoparticles by a covalent bond, and
• wherein the first layer includes a first polyurethane including a repeating unit represented by Formula 2-1, the second layer includes a second polyurethane including a repeating unit represented by Formula 2-2, and the third layer includes a third polyurethane including a repeating unit represented by Formula 2-3,
• wherein in Formulae 2-1, 2-2, and 2-3, R1 is a chain or branched alkylene of 2 to 12 carbon atoms, R2 is an alkylene of 2 to 12 carbon atoms or a phenylene, R3 is an ether group of 2 to 12 carbon atoms, R4 is an aryl group of 6 to 20 carbon atoms, R5 is an alkylene of 4 to 20 carbon atoms or a cycloalkylene of 6 to 20 carbon atoms, x, y, and z are integers of 10 to 10000, independently, and a, b, and c are integers of 1 or larger, independently,
• wherein the first modulus, the second modulus, and the third modulus refers to a Young's modulus.