Forgery prevention apparatus to prevent delamination and forgery authentication method using the same

1. An anti-counterfeiting apparatus comprising:

a first layer formed of a flexible material and including a high-corrugation region and a low-corrugation region;

a second layer adhered to the first layer, formed in a pattern on an upper portion of the high-corrugation region and formed of a material having a Young's modulus greater than that of the first layer;

a third layer adhered to the first layer to cover the low-corrugation region and the second layer, and formed of a material having a Young's modulus greater than that of the first layer and a Young's modulus smaller than that of the second layer; and

an adhesive layer configured to adhere the first layer, the second layer and the third layer,

wherein each of the first layer, the second layer, the third layer and the adhesive layer satisfies Equation 2:

r

>

❘

"\[LeftBracketingBar]"

X

i

-

d

n

❘

"\[RightBracketingBar]"

ε

Yi

[

Equation

⁢

2

]

wherein X i is a distance between an outer surface of the first layer and a center plane of each corresponding layer,

d n is a distance between the outer surface of the first layer and a neutral plane,

ε Yi is a yield strain of each corresponding layer, and

r is a radius of curvature of the anti-counterfeiting apparatus, and

wherein the center plane bisects the thickness of each corresponding layer and the neutral plane has an average stiffness of all layers of the anti-counterfeiting apparatus.

2. The anti-counterfeiting apparatus according to claim 1 , wherein the adhesive layer comprises a first adhesive layer configured to adhere the first layer and the second layer, and a second adhesive layer configured to adhere the first layer and the third layer.

3. The anti-counterfeiting apparatus according to claim 1 , wherein the distance between the outer surface of the first layer and the neutral plane (d n ) satisfies Equation 6:

d

n

=

∑

i

[

K

i

⁢

X

i

⁢

Z

i

]

∑

i

[

K

i

⁢

Z

i

]

[

Equation

⁢

6

]

wherein

X i is the distance between the outer surface of the first layer and the center plane of each corresponding layer, which refers to one of first layer, second layer, third layer, and adhesive layer,

K i is an elastic modulus of each corresponding layer, and

Z i is a thickness of each corresponding layer.

4. The anti-counterfeiting apparatus according to claim 3 , wherein the elastic modulus and the thickness of the first layer, the second layer, the third layer and the adhesive layer are determined so that the neutral plane is located between the first layer and the third layer.

5. The anti-counterfeiting apparatus according to claim 1 , wherein each of the first layer, the second layer, the third layer and the adhesive layer satisfies Equation 7:

r

>

12

⁢

R

2

⁢

❘

"\[LeftBracketingBar]"

X

i

-

d

n

❘

"\[RightBracketingBar]"

π

2

⁢

Z

i

2

[

Equation

⁢

7

]

wherein X i is a distance between the outer surface of the first layer and a center plane of a delaminated layer in which a delamination occurs,

Z i is a thickness of the delaminated layer,

d n is a distance between the outer surface of the first layer and a neutral plane,

R is a length of micropores of the adhesive layer, and r is the radius of curvature of the anti-counterfeiting apparatus,

wherein the center plane bisects the thickness of each corresponding layer and the neutral plane has an average stiffness of all layers of the anti-counterfeiting apparatus.

6. The anti-counterfeiting apparatus according to claim 5 , wherein, when a plurality of adhesive layers are comprised, an average length of the micropores R m satisfies Equation 10:

R

m

=

π

⁢

Z

i

(

r

m

12

⁢

❘

"\[LeftBracketingBar]"

X

i

-

d

n

❘

"\[RightBracketingBar]"

)

1

/

2

[

Equation

⁢

10

]

wherein X i is the distance between the outer surface of the first layer and the center plane of the delaminated layer,

Z i is the thickness of the delaminated layer, d n is the distance between the outer surface of the first layer and the neutral plane, and

r m is an average value of the curvature radii at the time of occurring the delamination when the anti-counterfeiting apparatus is bent.

7. The anti-counterfeiting apparatus according to claim 1 , wherein a guide portion which satisfies a condition for the radius of curvature r is formed on an upper portion of the third layer.

8. The anti-counterfeiting apparatus according to claim 5 , wherein a guide portion which satisfies a condition for the radius of curvature r is formed on an upper portion of the third layer.

9. The anti-counterfeiting apparatus according to claim 1 , wherein a guide portion which satisfies a condition for the radius of curvature r is formed inside the first layer.

10. The anti-counterfeiting apparatus according to claim 5 , wherein a guide portion which satisfies a condition for the radius of curvature r is formed inside the first layer.

11. An anti-counterfeiting authentication method comprising:

applying an external force to the anti-counterfeiting apparatus of claim 1 so as to form corrugations in the second layer and the third layer;

respectively forming corrugations having a different wavelength in the second layer and the third layer while a buckling effect appears due to different stress distributions and surface strains of the respective layers depending on a difference in the Young's modulus; and

determining whether there is forgery through images formed by expressing different structural colors due to incident lights in the high-corrugation region and the low-corrugation region on the first layer where grating structures of different shapes are formed by an arrangement of the corrugations.