PRESSURE-SENSITIVE ADHESIVE
The present application can provide a pressure-sensitive adhesive suitable for a flexible device, and a device comprising the same. In one example, the present application can provide a pressure-sensitive adhesive that is applied to a flexible device to effectively respond to repeated deformation and recovery, does not cause defects before and after deformation, and has excellent recoverability as well.
1 . A pressure-sensitive adhesive having a maximum stress S MAX of 1 MPa or less as measured while maintaining a strain of 100% applied to the pressure-sensitive adhesive for 1200 seconds, the strain of 100% obtained within 0.05 seconds by a shear force applied at −20° C., and having a stress S 1200 of 12,000 Pa or less at a time point when the strain of 100% is maintained for 1200 seconds.
2 . A pressure-sensitive adhesive, wherein ΔS X1 of Equation 1 below is 3,500 Pa/time or less, and S MAX50 of Equation 1 below is 250,000 Pa or less:
Δ
S
X
1
=
0.02
×
(
S
MAX
1
-
S
MAX
50
)
[
Equation
1
]
wherein, S MAX1 is a maximum stress (unit: Pa) identified within a time period of 0 seconds to 2 seconds in a process of applying a shear force to the pressure-sensitive adhesive for 100 seconds according to Equation 2 below at −20° C., and S MAX50 is a maximum stress (unit: Pa) identified within a time period of 99 seconds to 100 seconds in the process of applying the shear force to the pressure-sensitive adhesive for 100 seconds according to Equation 2 below at −20° C.:
Sin
wave
equation
=
4
×
sin
(
1
.
5
7
5
×
t
)
[
Equation
2
]
wherein, t is a time (unit: sec).
3 . The pressure-sensitive adhesive according to claim 1 , wherein a ratio (S MAX /S 1200 ) of the maximum stress S MAX relative to the stress S 1200 is in a range from 30 to 60.
4 . The pressure-sensitive adhesive according to claim 1 , wherein ΔS X2 of Equation 3 below is 15,000 Pa/time or less:
Δ
S
X
2
=
0
.
1
×
(
S
MAX
1
-
S
MAX
10
)
[
Equation
3
]
wherein, S MAX1 is a maximum stress (unit: Pa) identified within a time period of 0 seconds to 2 seconds in a process of applying a shear force to the pressure-sensitive adhesive for 100 seconds according to Equation 2 below at −20° C., and S MAX10 is a maximum stress (unit: Pa) identified within a time period of 19 seconds to 20 seconds in the process of applying the shear force to the pressure-sensitive adhesive for 100 seconds according to Equation 2 below at −20° C.:
Sin
wave
equation
=
4
×
sin
(
1
.
5
7
5
×
t
)
[
Equation
2
]
wherein, t is a time (unit: sec).
5 . The pressure-sensitive adhesive according to claim 1 , wherein ΔS X3 of Equation 4 below is 700 Pa/time or less:
Δ
S
X
3
=
0
.
0
2
5
×
(
S
MAX
10
-
S
MAX
50
)
[
Equation
4
]
wherein, S MAX10 is a maximum stress (unit: Pa) identified within a time period of 19 seconds to 20 seconds in a process of applying a shear force to the pressure-sensitive adhesive for 100 seconds according to Equation 2 below at −20° C., and S MAX50 is a maximum stress (unit: Pa) identified within a time period of 99 seconds to 100 seconds in the process of applying the shear force to the pressure-sensitive adhesive for 100 seconds according to Equation 2 below at −20° C.:
Sin
wave
equation
=
4
×
sin
(
1
.
5
7
5
×
t
)
[
Equation
2
]
wherein, t is a time (unit: sec).
6 . The pressure-sensitive adhesive according to claim 1 , wherein ΔS XL1 of Equation 5 below is 600,000 Pa or less:
Δ
S
XL
1
=
(
S
MAX
1
-
S
LAST
1
)
[
Equation
5
]
wherein, S MAX1 is a maximum stress (unit: Pa) identified within a time period of 0 seconds to 2 seconds in a process of applying a shear force to the pressure-sensitive adhesive for 100 seconds according to Equation 2 below at −20° C., and S LAST1 is a stress (unit: Pa) identified at 2 seconds during the process of applying the shear force to the pressure-sensitive adhesive for 100 seconds according to Equation 2 below at −20° C.:
Sin
wave
equation
=
4
×
sin
(
1
.
5
7
5
×
t
)
[
Equation
2
]
wherein, t is a time (unit: sec).
7 . The pressure-sensitive adhesive according to claim 1 , wherein ΔS XL50 of Equation 6 below is 500,000 Pa or less:
Δ
S
XL
50
=
(
S
MAX
50
-
S
LAST
50
)
[
Equation
6
]
wherein, S MAX50 is a maximum stress (unit: Pa) identified within a time period of 99 seconds to 100 seconds in a process of applying a shear force to the pressure-sensitive adhesive for 100 seconds according to Equation 2 below at −20° C., and S LAST50 is a stress (unit: Pa) identified at 100 seconds during the process of applying the shear force to the pressure-sensitive adhesive for 100 seconds according to Equation 2 below at −20° C.:
Sin
wave
equation
=
4
×
sin
(
1
.
5
7
5
×
t
)
[
Equation
2
]
wherein, t is a time (unit: sec).
8 . The pressure-sensitive adhesive according to claim 1 , wherein ΔS XL10 of Equation 7 below is 500,000 Pa or less:
Δ
S
XL
10
=
(
S
MAX
10
-
S
LAST
10
)
[
Equation
7
]
wherein, S MAX10 is a maximum stress (unit: Pa) identified within a time period of 19 seconds to 20 seconds in a process of applying a shear force to the pressure-sensitive adhesive for 100 seconds according to Equation 2 below at −20° C., and S LAST10 is a stress (unit: Pa) identified at 20 seconds during the process of applying the shear force to the pressure-sensitive adhesive for 100 seconds according to Equation 2 below at −20° C.:
Sin
wave
equation
=
4
×
sin
(
1
.
5
7
5
×
t
)
[
Equation
2
]
wherein, t is a time (unit: sec).
9 . The pressure-sensitive adhesive according to claim 1 , wherein a recovery rate is at least 70%.
10 . The pressure-sensitive adhesive according to claim 1 , wherein an elastic modulus at −20° C. is 1 MPa or less, and a maximum stress in a linear section of a strain-stress curve for identifying the elastic modulus is 30,000 Pa or less.
11 . The pressure-sensitive adhesive according to claim 1 , comprising a pressure-sensitive adhesive polymer.
12 . The pressure-sensitive adhesive according to claim 11 , wherein the pressure-sensitive adhesive polymer is an acrylic copolymer having a glass transition temperature (Tg) and a melting temperature (Tm).
13 . The pressure-sensitive adhesive according to claim 12 , wherein the acrylic copolymer has the glass transition temperature of −30° C. or less and the melting temperature of −10° C. or less.
14 . The pressure-sensitive adhesive according to claim 12 , wherein a difference (Tm−Tg) between the melting temperature and the glass transition temperature is at least 5° C.
15 . The pressure-sensitive adhesive according to claim 12 , wherein the acrylic copolymer has a molecular weight distribution of more than 3, and the acrylic copolymer is cross-linked with a thermal cross-linking agent.
16 . The pressure-sensitive adhesive according to claim 12 , wherein the acrylic copolymer has a molecular weight distribution of 3 or less, and the acrylic copolymer is cross-linked with a radical cross-linking agent.
17 . The pressure-sensitive adhesive according to claim 12 , wherein the acrylic copolymer comprises an alkyl (meth)acrylate unit, a unit of Formula 1 below, and a polar functional group-containing unit:
wherein, R 1 represents hydrogen or an alkyl group, and R 2 represents an alkyl group with 11 to 13 carbon atoms.
18 . A pressure-sensitive adhesive film comprising a base film; and the pressure-sensitive adhesive of claim 1 formed on one side or both sides of the base film.
19 . A flexible device comprising:
a display panel configured to be capable of folding or rolling through one or more folding axes or rolling axes; and
the pressure-sensitive adhesive of claim 1 formed on one side or both sides of the display panel.