Pressure-sensitive adhesive
The present application may provide a pressure-sensitive adhesive with excellent reliability, which is applied to a flexible device, thereby effectively responding to repeated deformation and recovery, causing no defects (for example, observation of deformation traces and the like) before and after deformation, having excellent cuttability, workability, and recoverability, and causing no lifting, delamination, and/or bubble generation. The present application may also provide a pressure-sensitive adhesive film or an optical film, and a flexible device such as a foldable device or a rollable device, comprising the pressure-sensitive adhesive.
1 . A pressure-sensitive adhesive comprising a pressure-sensitive adhesive polymer,
wherein the pressure-sensitive adhesive polymer is an acrylic copolymer exhibiting a glass transition temperature and a melting temperature simultaneously, and
an absolute value of the change rate ΔG1′ of the storage elastic modulus of 1,700 or less according to Equation 1 below:
Δ
G
1
′
=
(
G
25
′
-
G
-
20
′
)
/
45
[
Equation
1
]
wherein, G′ 25 is the storage elastic modulus of the pressure-sensitive adhesive at 25° C., and G′ −20 is the storage elastic modulus of the pressure-sensitive adhesive at −20° C.;
wherein the storage elastic modulus at −20° C. is 70,000 to 100,000 Pa;
wherein the storage elastic modulus at 25° C. is at least 10,000 Pa;
wherein the storage elastic modulus at 60° C. is at least 10,000 Pa;
wherein an absolute value of the change rate ΔG2′ of the storage elastic modulus according to Equation 2 below is 1,100 or less:
Δ
G
2
′
=
(
G
60
′
-
G
-
20
′
)
/
80
[
Equation
2
]
wherein, G′ 60 is the storage elastic modulus of the pressure-sensitive adhesive at 60° C., and G′ −20 is the storage elastic modulus of the pressure-sensitive adhesive at −20° C.;
wherein an absolute value of the change rate ΔG3′ of the storage elastic modulus according to Equation 3 below is 600 or less:
Δ
G
3
′
=
(
G
60
′
-
G
25
′
)
/
35
[
Equation
3
]
wherein, ΔG3′ is the storage elastic modulus of the pressure-sensitive adhesive at 60° C., and G′25 is the storage elastic modulus of the pressure-sensitive adhesive at 25° C.;
wherein the TM of Equation 4 below is at least 400 um·MPa −1 :
TM
=
D
/
G
-
20
′
[
Equation
4
]
wherein, D is the thickness of the pressure-sensitive adhesive, and G′ −20 is the storage elastic modulus of the pressure-sensitive adhesive at −20° C.
2 . The pressure-sensitive adhesive according to claim 1 , wherein the acrylic copolymer has a glass transition temperature of −30° C. or less and a melting temperature of −10° C. or less.
3 . The pressure-sensitive adhesive according to claim 1 , wherein the acrylic copolymer has a difference (Tm−Tg) between the melting temperature and the glass transition temperature of at least 15° C.
4 . The pressure-sensitive adhesive according to claim 1 , 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.
5 . The pressure-sensitive adhesive according to claim 4 , wherein the alkyl (meth)acrylate unit has a linear or branched alkyl group with 1 to 10 carbon atoms, and the polar functional group-containing unit is a hydroxy group-containing monomer unit.
6 . The pressure-sensitive adhesive according to claim 4 , wherein the acrylic copolymer contains the alkyl (meth)acrylate unit in an amount of 10 to 60 wt %.
7 . The pressure-sensitive adhesive according to claim 4 , wherein the acrylic copolymer contains 80 to 600 parts by weight of the Formula 1 relative to 100 parts by weight of the alkyl (meth)acrylate unit.
8 . The pressure-sensitive adhesive according to claim 4 , wherein the acrylic copolymer contains 10 to 200 parts by weight of the polar functional group-containing unit relative to 100 parts by weight of the alkyl (meth)acrylate unit.
9 . The pressure-sensitive adhesive according to claim 1 , wherein the pressure-sensitive adhesive polymer does not contain a monomer unit of Formula 2 below, or contains the monomer unit of Formula 2 below in a ratio of 0.1 wt % or less based on the total weight of the pressure-sensitive adhesive polymer:
wherein, R 1 represents hydrogen or an alkyl group, and R 3 is an aromatic ketone group or a (meth)acryloyl group.
10 . The pressure-sensitive adhesive according to claim 1 , further comprising a radical cross-linking agent.
11 . The pressure-sensitive adhesive according to claim 1 , which is a cured product of a solventless or syrup pressure-sensitive adhesive composition.
12 . 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.
13 . A flexible device comprising:
a display panel configured to be capable of folding or rolling through folding axis or rolling axis; and
the pressure-sensitive adhesive of claim 1 present on one side or both sides of the display panel.