Pressure-sensitive adhesive composition for foldable display

Abstract

The present application relates to a pressure-sensitive adhesive composition for a foldable display and a use thereof. The pressure-sensitive adhesive composition of the present application has excellent bending reliability while having appropriate adhesive force and cohesive force, thereby being useful for forming a pressure-sensitive adhesive layer for a foldable display having improved release force.

Claims

1. A pressure-sensitive adhesive composition for a foldable display comprising: a first pressure-sensitive adhesive comprising a first silicone gum and a first MQ resin, and having a peel force on a glass substrate, as measured at a peel rate of 0.3 m/min and a peel angle of 180 degrees, of 10 gf/in or less; and a second pressure-sensitive adhesive comprising a second silicone gum and a second MQ resin, and having a peel force on a glass substrate, as measured at a peel rate of 0.3 m/min and a peel angle of 180 degrees, of 200 gf/in to 400 gf/in, wherein said first pressure-sensitive adhesive is contained in an amount of 5 wt % to 50 wt % relative to the total solid content of the composition, wherein MQ resin is a silicone compound having at least a three-dimensional reticular steric molecular structure comprising a monofunctional siloxane unit (M Unit) and a tetrafunctional siloxane unit (Q unit), and the composition satisfies Equation 1 below:
A<20 gf/in[Equation 1] wherein, A means a peel force of a pressure-sensitive adhesive layer formed by curing the pressure-sensitive adhesive composition on a fluorine-based release film, as measured at a peel rate of 0.3 m/min and a peel angle of 180 degrees.

2. The pressure-sensitive adhesive composition for a foldable display according to claim 1, wherein the first or second silicone gum is represented by Formula 1 below: ##STR00003## wherein, R.sup.1 and R.sup.6 are each independently a silyl group or silanol group with or without an alkyl group, an alkenyl group or an aryl group, R.sup.2 to R.sup.5 are each independently an alkyl group, an alkenyl group or an aryl group, and n and m are each independently an integer in a range of 1 to 10,000.

3. The pressure-sensitive adhesive composition for a foldable display according to claim 1, wherein the first pressure-sensitive adhesive comprises the first MQ resin in a content of less than 5 wt %.

4. The pressure-sensitive adhesive composition for a foldable display according to claim 1, wherein the first silicone gum has a number average molecular weight in a range of 400,000 to 800,000.

5. The pressure-sensitive adhesive composition for a foldable display according to claim 1, wherein the first silicone gum has a vinyl group content in a range of 0.5 to 1.5 mol %.

6. The pressure-sensitive adhesive composition for a foldable display according to claim 1, wherein the second pressure-sensitive adhesive has a storage elastic modulus measured at 40 C. of 10 Pa or less.

7. The pressure-sensitive adhesive composition for a foldable display according to claim 1, wherein the second pressure-sensitive adhesive comprises the second MQ resin in a content of 40 wt % or less.

8. The pressure-sensitive adhesive composition for a foldable display according to claim 1, wherein the second silicone gum is a linear polydimethylsiloxane containing hydroxy groups at both ends.

9. The pressure-sensitive adhesive composition for a foldable display according to claim 1, wherein a storage elastic modulus (G) after curing is 510.sup.6 Pa or less within a temperature range of 40 C. to 90 C.

10. A foldable display comprising a pressure-sensitive adhesive layer which is a cured product of the pressure-sensitive adhesive composition for a foldable display of claim 1 attached to an adherend.

11. The foldable display according to claim 10, wherein the adherend is a base film, and said base film and said pressure-sensitive adhesive layer form covalent bonds via silanol groups contained in said pressure-sensitive adhesive layer.

12. The foldable display according to claim 10, wherein the pressure-sensitive adhesive layer has a peel force on the adherend as measured at a peel rate of 0.3 m/min and a peel angle of 180 degrees of 2,000 gf/in or more.

Description

MODE FOR INVENTION

(1) Hereinafter, the pressure-sensitive adhesive composition for a foldable display according to the present application and the display comprising the same will be described in detail with reference to Examples and Comparative Examples, but the following examples are only examples according to the present application, and thus do not limit the technical idea of the present application.

(2) The physical properties of the pressure-sensitive adhesive composition of the present application were evaluated by the following methods.

(3) 1. Measurement of Storage Elastic Modulus

(4) A pressure-sensitive adhesive composition prepared in Examples and Comparative Examples was coated between release films and cured, and then tailored to a size of 15 cm25 cm, and laminated several times to have a thickness of about 1 mm, after removing the release film on one side. Subsequently, the laminate was tailored into a circle having a diameter of 8 mm and compressed using glass, and then a sample was prepared by allowing the laminate to stand overnight to improve wetting at the interfaces between the layers and removing bubbles generated upon lamination. Subsequently, the sample was placed on a parallel plate, the gap was adjusted, the zero point of Normal & Torque was set, and the storage elastic modulus was measured after confirming stabilization of Normal force.

(5) (1) Measuring Instruments and Measuring Conditions

(6) Measuring instrument: ARES-RDA equipped with a forced convection oven, TA Instruments Inc. (G2 series Rheometer)

(7) (2) Measurement Conditions

(8) Geometry: 8 mm parallel plate

(9) Interval: about 1 mm

(10) Test type: dynamic strain frequency sweep

(11) Strain=0.1 [%]

(12) Initial temperature: 40 C., final temperature: 90 C.

(13) Frequency: 6.2 rad/s

(14) 2. Peel Force Measurement

(15) The pressure-sensitive adhesive layer prepared according to Examples and Comparative Examples was attached to a glass substrate or a surface-treated PI base film as an adherend and then subjected to aging under a condition of 50 C. and 5 atm for 1 hour or at room temperature for 3 days. After aging, the peel force was measured at a peel rate of 0.3 m/min and a peel angle of 180 degrees at room temperature using a tensile tester (Texture Analyzer).

(16) 3. Measurement of Releasing Peel Force

(17) After the pressure-sensitive adhesive layers according to Examples or Comparative Examples were each set to have a width of 1 inch and stored under 25 C. and 50% relative humidity for 1 week, peel force of the pressure-sensitive adhesive layer on medium peeling type and light peeling type fluorine-based release films (TACS TS-502S) (peel rate: 0.3 m/min, peel angle: 180) was measured.

(18) The measurement was carried out under a constant temperature and humidity condition, and the peel force was measured using a texture analyzer on the basis of ASTM 3330.

Example 1

(19) Preparation of Pressure-Sensitive Adhesive Composition (A1)

(20) A first pressure-sensitive adhesive comprising a first polysiloxane gum with a vinyl group content of 0.5 mol % and a number average molecular weight of about 600,000, and about 0.001 wt % or so of a MQ resin with a structure of Formula 2 (R is an alkyl group having 1 to 2 carbon atoms), and having a peel force on a glass substrate of about 2 gf/in, and a second pressure-sensitive adhesive comprising a second polydimethylsiloxane silicone gum containing hydroxy groups at both ends and having a number average molecular weight of 700,000, and about 38 wt % of the MQ resin, and having a peel force on a glass substrate of about 337 gf/in were mixed with a solvent, but a pressure-sensitive adhesive composition (A1) was prepared by adjusting the content of the first pressure-sensitive adhesive to about 10 wt % relative to the total solid content of the composition.

(21) Formation of Pressure-Sensitive Adhesive Layer (B1)

(22) The pressure-sensitive adhesive composition (A1) was coated on the primer-treated PET base material and cured to form a pressure-sensitive adhesive layer (B1), where the pressure-sensitive adhesive layer (B1) was subjected to surface modification.

Example 2

(23) A pressure-sensitive adhesive composition (A2) was prepared in the same manner as in Example 1 except that the content of the first pressure-sensitive adhesive was adjusted to about 30 wt % relative to the total solid content of the composition, and a pressure-sensitive adhesive layer (B2) was formed using this composition and subjected to surface modification.

Comparative Example 1

(24) A pressure-sensitive adhesive composition (A3) composed of only the first pressure-sensitive adhesive according to Example 1 and a solvent was prepared, and a pressure-sensitive adhesive layer (B3) was formed in the same manner as in Example 1 using this composition and subjected to surface modification.

Comparative Example 2

(25) A pressure-sensitive adhesive composition (A4) composed of only the second pressure-sensitive adhesive according to Example 1 and a solvent was prepared, and a pressure-sensitive adhesive layer (B4) was formed in the same manner as in Example 1 using this composition and subjected surface modification.

Experimental Example 1Measurement of Peel Force on Glass Substrate or PI Base Film

(26) The peel forces of the pressure-sensitive adhesive layers according to Examples 1 and 2 and Comparative Examples 1 and 2 on a glass substrate or a PI base film were measured, and the results were shown in Table 1 below.

(27) TABLE-US-00001 TABLE 1 Comparative Example Example 1 2 1 2 Peel force on glass substrate (gf/in) 32 28 2 337 Peel force on PI base film (gf/in) 2,200 2,700 1200

(28) As described in Table 1 above, it could be confirmed that when the pressure-sensitive adhesive layers were formed using the pressure-sensitive adhesive compositions according to Examples 1 and 2 of the present application, they had excellent adhesive force on the glass substrate or the PI base film, but in the case of the low pressure-sensitive adhesive layer according to Comparative Example 1, although the change of the storage elastic modulus was small as shown in Table 2 below, they were not suitable as a pressure-sensitive adhesive composition for a foldable display due to the rarely measured low pressure-sensitive adhesive force.

Experimental Example 2Measurement of Storage Elastic Modulus

(29) In order to examine the storage elastic modulus change rate depending on temperatures after curing of the compositions according to Examples 1 and 2, the storage elastic modulus at 40 C. and 90 C. was measured according to the above-described measuring method using an ARES-RDA, an equipment of TA instruments, equipped with a forced convection oven and the results were shown in Table 2.

(30) TABLE-US-00002 TABLE 2 Example Comparative Example 1 2 1 2 Storage elastic 1.8 10.sup.5 Pa 1.8 10.sup.5 Pa 8 10.sup.5 Pa 3 10.sup.5 Pa modulus at 40 C. (Pa) Storage elastic 1.1 10.sup.5 Pa 1.7 10.sup.5 Pa 7 10.sup.5 Pa 3 10.sup.4 Pa modulus at 90 C. (Pa)

Experimental Example 3Measurement of Releasing Peel Force

(31) After the pressure-sensitive adhesive layers according to Examples 1 and 2 and Comparative Examples 1 and 2 were each set to have a width of 1 inch and stored under 25 C. and 50% relative humidity for 1 week, the pressure-sensitive adhesive layers were each attached to medium peeling type and light peeling type fluorine-based release films and then it was measured at a peel rate of 0.3 m/min and peel angle of 180 degrees using a texture analyzer on the basis of ASTM3330, and the results were shown in Table 3 below.

(32) TABLE-US-00003 TABLE 3 Comparative Example Example Condition 1 2 1 2 Light peeling type fluorine-based 7 4 2 9.1 release film (gf/in) Medium peeling type fluorine-based 11 8 76.8 release film (gf/in)

(33) As described in Experimental Examples 1 to 3 and Tables 1 to 3, in the case of the pressure-sensitive adhesive layers according to Examples 1 and 2, since they have appropriate adhesive force and cohesive force and exhibit the storage elastic modulus at a temperature of 40 C. of 5.010.sup.6 Pa or less, not only the folding reliability required in the foldable display can be ensured, but also the releasing peel force can be maintained in a very low range to exhibit excellent release force.