Foldable backplate, method for manufacturing foldable backplate, and foldable display device comprising same

1. A foldable back plate comprising:

a polyimide (PI) substrate;

a first adhesive layer provided on a surface of the polyimide substrate; and

a second adhesive layer provided on a surface opposite to the surface of the polyimide substrate in contact with the first adhesive layer,

wherein a storage modulus (G1) at 20° C. of the polyimide substrate satisfies Equation 1,

1 GPa≤ G 1≤5 GPa  [Equation 1]

wherein, an initial adhesive force of the first adhesive layer is at least 500 gf/inch, and

an initial adhesive force of the second adhesive layer is at least 500 gf/inch, and

wherein the initial adhesive force is measured at 23° C. after attaching a polyimide (PI) to the first adhesive layer or to the second adhesive layer on a surface opposite of the surface of the first adhesive layer or the second adhesive layer that is in contact with the polyimide substrate and then the polyimide-attached first adhesive layer or the polyimide-attached second adhesive layer standing at 23° C. for 2 hours.

2. The foldable back plate of claim 1 , wherein a storage modulus at −30° C. of each of the first adhesive layer and the second adhesive layer and,

a storage modulus at 60° C. of each of the first adhesive layer and the second adhesive layer satisfy Equations 2 and 3 below:

1×10 4 Pa≤ G 2≤1×10 6 Pa  [Equation 2]

1×10 4 Pa≤ G 3≤1×10 6 Pa  [Equation 3]

wherein G2 is a storage modulus at −30° C. of each of the first adhesive layer and the second adhesive layer and

G3 is a storage modulus at 60° C. of each of the first adhesive layer and the second adhesive layer.

3. The foldable back plate of claim 1 , wherein the initial adhesive force (gf/inch) of each of the first adhesive layer and the second adhesive layer and

a late adhesive force (gf/inch) of each of the first adhesive layer and the second adhesive layer satisfy Equation 4:

A 1×0.8≤ A 2  [Equation 4]

wherein A1 is the initial adhesive force (gf/inch) of each of the first adhesive layer and the second adhesive layer and

A2 is the late adhesive force (gf/inch) of each of the first adhesive layer and the second adhesive layer, and

wherein the late adhesive force is measured after the polyimide-attached first adhesive layer or the polyimide-attached second adhesive layer standing at 60° C./humidity 90% for 20 days.

4. The foldable back plate of claim 1 , wherein the polyimide substrate has an elongation at break at 20° C. of 20% or more and 200% or less.

5. The foldable back plate of claim 1 , wherein the polyimide substrate has a heat shrinkage at 200° C. of 0.1% or less.

6. The foldable back plate of claim 1 , wherein the polyimide substrate has a thickness of 10 μm or more and 150 μm or less.

7. The foldable back plate of claim 1 , wherein each of the first adhesive layer and the second adhesive layer has a thickness of 10 μm or more and 100 μm or less.

8. The foldable back plate of claim 1 , further comprising:

a first release film provided on an opposite surface of the first adhesive layer in contact with the polyimide substrate; and

a second release film provided on an opposite surface of the second adhesive layer in contact with the polyimide substrate,

wherein a peel force at 23° C. of the second release film from the second adhesive layer is 20 gf/inch or less, and

a peel force at 23° C. of the first release film from the first adhesive layer is lower than the peel force of the second release film from the second adhesive layer.

9. The foldable back plate of claim 8 , wherein the peel force at 23° C. of the first release film from the first adhesive layer is 15 gf/inch or less.

10. The foldable back plate of claim 8 , wherein each of the first release film and the second release film has a thickness of 10 μm or more and 150 μm or less.

11. The foldable back plate of claim 8 , wherein the first release film and the second release film are silicone-based films.

12. The foldable back plate of claim 8 , wherein each of the first release film and the second release film has a surface resistance of 10 10 Ω/sq or less at 500V or less.

13. A foldable display device comprising the foldable back plate according to claim 1 .

14. A method of manufacturing a foldable back plate comprising:

providing a polyimide (PI) substrate;

coating a first adhesive layer on a surface of the polyimide substrate;

laminating a first release film on a surface opposite to the surface of the first adhesive layer in contact with the polyimide substrate;

providing a second release film;

coating a second adhesive layer on a surface of the second release film; and

laminating a surface opposite to the surface of the second adhesive layer in contact with the second release film on a surface opposite to the surface of the polyimide substrate in contact with the first adhesive layer,

wherein a storage modulus (G1) at 20° C. of the polyimide substrate satisfies Equation 1:

1 GPa≤ G 1≤5 GPa  [Equation 1]

a peel force at 23° C. of the second release film from the second adhesive layer is 20 gf/inch or less, and

a peel force at 23° C. of the first release film from the first adhesive layer is lower than the peel force of the second release film from the second adhesive layer.

15. The method of claim 14 , wherein the coating the first adhesive layer and the coating the second adhesive layer are carried out by direct coating.