PROTECTING FILM FOR COVER WINDOW OF FLEXIBLE DISPLAY DEVICE, COVER WINDOW AND FLEXIBLE DISPLAY DEVICE COMPRISING THE SAME

Abstract

The present disclosure relates to a protecting film for a cover window of a flexible display device in which a first hard coating layer containing 3 parts by weight or less of inorganic particles based on 100 parts by weight of a binder resin; a second hard coating layer containing 10 to 45 parts by weight of inorganic particles based on 100 parts by weight of a binder resin; and a light-transmitting substrate are sequentially laminated, wherein the first hard coating layer and the second hard coating layer have a specific thickness ratio, a cover window and a display device including the same.

Claims

1. A protecting film for a cover window of a flexible display device comprising a first hard coating layer containing a binder resin and 3 parts by weight or less of inorganic particles based on 100 parts by weight of the binder resin; a second hard coating layer containing a binder resin and 10 to 45 parts by weight of inorganic particles based on 100 parts by weight of the binder resin; and a light-transmitting substrate are sequentially laminated, wherein a thickness ratio of the first hard coating layer and the second hard coating layer is 10:90 to 40:60.

2. The protecting film for a cover window of a flexible display device of claim 1, wherein cracks do not occur when both sides of the protecting film for a cover window are folded and unfolded at 90 degrees with respect to a bottom surface 100,000 times at room temperature with a 4 mm gap in the middle of the protecting film for a cover window.

3. The protecting film for a cover window of a flexible display device of claim 1, wherein the first hard coating layer has a pencil hardness of at least H under a load of 750 g.

4. The protecting film for a cover window of a flexible display device of claim 1, wherein a surface of the first hard coating layer has a water contact angle of at least 105.

5. The protecting film for a cover window of a flexible display device of claim 1, wherein the protecting film for a cover window has a transmittance with respect to light having a wavelength of 550 nm of 90.0% or more, and a haze of 1.0% or less.

6. The protecting film for a cover window of a flexible display device of claim 1, wherein a thickness of the first hard coating layer is 1 m to 10 m.

7. The protecting film for a cover window of a flexible display device of claim 1, wherein a thickness of the second hard coating layer is 1 m to 10 m.

8. The protecting film for a cover window of a flexible display device of claim 1, wherein a total thickness of the first hard coating layer and the second hard coating layer is 2 m to 17 m.

9. The protecting film for a cover window of a flexible display device of claim 1, wherein the binder resin included in each of the first hard coating layer and the second hard coating layer contains a multifunctional (meth)acrylate-based compound.

10. The protecting film for a cover window of a flexible display device of claim 9, wherein the first hard coating layer and the second hard coating layer each independently contain 50 parts by weight or more of the multifunctional (meth)acrylate-based compound based on 100 parts by weight of the binder resin.

11. The protecting film for a cover window of a flexible display device of claim 9, wherein the multifunctional (meth)acrylate-based compound is modified with at least one selected from the group consisting of ethylene oxide, propylene oxide, urethane, caprolactone, epoxy, and ester.

12. The protecting film for a cover window of a flexible display device of claim 1, wherein the first hard coating layer further contains at least one additive selected from the group consisting of a fluorine-based additive, a silicone-based additive, and a fluorine-silicone-based additive.

13. The protecting film for a cover window of a flexible display device of claim 1, wherein the light-transmitting substrate comprises at least one selected from the group consisting of polyimide (PI), polyimideamide, polyetherimide (PEI), polyethyleneterephtalate (PET), polyethylenenaphthalate (PEN), polyetheretherketon (PEEK), cyclic olefin polymer (COP), polyacrylate (PAC), polymethylmethacrylate (PMMA), and triacetylcellulose (TAC).

14. The protecting film for a cover window of a flexible display device of claim 1, wherein a total thickness of the first hard coating layer, the second hard coating layer and the light-transmitting substrate is 40 m to 150 m.

15. A cover window of a flexible display device comprising the protecting film for a cover window of a flexible display device of claim 1.

16. The cover window of a flexible display device of claim 15, further comprising a glass cover or a plastic film cover formed on one surface of the protecting film for a cover window and having a thickness of 20 m to 180 m.

17. A display device comprising the cover window of a flexible display device of claim 15.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0092] FIG. 1 schematically shows a method of performing a bending durability test of Experimental Example 3.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0093] Hereinafter, the function and effect of the present invention will be described in more detail with specific embodiments. However, these embodiments are merely presented as an example of the invention, and the scope of the invention is not defined thereby.

Preparation Examples: Preparation of Coating Solution for Forming Hard Coating Layer

Preparation Example 1-1

[0094] 100 g of MF001 (manufacturer: Daiichi Kogyo Seiyaku, 5- to 6-functional, ethylene oxide-modified) as a multifunctional acrylate-based compound, 2 g of RS-537 (manufacturer: DIC) as a fluorine-based additive, 2 g of 1184 (manufacturer: Ciba) as a photoinitiator, and 100 g of methyl isobutyl ketone as a solvent were mixed to prepare a coating solution for forming a first hard coating layer.

Preparation Example 1-2

[0095] 100 g of CN9013 (manufacturer: Sartomer, 9-functional, urethane-modified) as a multifunctional acrylate-based compound, 2 g of RS-537 (manufacturer: DIC) as a fluorine-based additive, 2 g of 1907 (manufacturer: Ciba) as a photoinitiator, and 100 g of methyl isobutyl ketone as a solvent were mixed to prepare a coating solution for forming a first hard coating layer.

Preparation Example 1-3

[0096] 100 g of trimethylolpropane triacrylate (manufacturer: Cytec, weight average molecular weight: 296 g/mol, acrylate equivalent weight: 99 g/mol) as a multifunctional acrylate-based compound, 2 g of RS-537 (manufacturer: DIC) as a fluorine-based additive, 2 g of 1184 (manufacturer: Ciba) as a photoinitiator, and 100 g of methyl isobutyl ketone as a solvent were mixed to prepare a coating solution for forming a first hard coating layer.

Preparation Example 1-4

[0097] 100 g of MF001 (manufacturer: Daiichi Kogyo Seiyaku, 5- to 6-functional, ethylene oxide-modified) as a multifunctional acrylate-based compound, 2 g of RS-537 (manufacturer: DIC) as a fluorine-based additive, 67 g of MEK-AC-4130Y (silica sol, manufacturer: Nissan Chemical, diameter: 50 nm, solid content: 30%) as inorganic particles, 2 g of 1184 (manufacturer: Ciba) as a photoinitiator, and 100 g of methyl isobutyl ketone as a solvent were mixed to prepare a coating solution for forming a first hard coating layer.

Preparation Example 2-1

[0098] 50 g of trimethylolpropane triacrylate (manufacturer: Cytec, weight average molecular weight: 296 g/mol, acrylate equivalent weight: 99 g/mol) as a multifunctional acrylate-based compound, 50 g of PS4040 (manufacturer: Miwon, weight average molecular weight: 1300 g/mol, acrylate equivalent weight: 325, 4-functional, ester-modified) as a multifunctional acrylate-based compound, 67 g of MEK-AC-4130Y (silica sol, manufacturer: Nissan Chemical, diameter: 50 nm, solid content: 30%) as inorganic particles, 2 g of 1184 (manufacturer: Ciba) as a photoinitiator, and 100 g of methyl isobutyl ketone as a solvent were mixed to prepare a coating solution for forming a second hard coating layer.

Preparation Example 2-2

[0099] 50 g of trimethylolpropane triacrylate (manufacturer: Cytec, weight average molecular weight: 296 g/mol, acrylate equivalent weight: 99 g/mol) as a multifunctional acrylate-based compound, 50 g of M244 (manufacturer: Miwon, weight average molecular weight: 468 g/mol, acrylate equivalent weight: 234 g/mol, 2-functional, epoxy-modified) as a multifunctional acrylate-based compound, 67 g of MEK-AC-4130Y (silica sol, manufacturer: Nissan Chemical, diameter: 50 nm, solid content: 30%) as inorganic particles, 2 g of 1184 (manufacturer: Ciba) as a photoinitiator, and 100 g of methyl isobutyl ketone as a solvent were mixed to prepare a coating solution for forming a second hard coating layer.

Preparation Example 2-3

[0100] 50 g of trimethylolpropane triacrylate (manufacturer: Cytec, weight average molecular weight: 296 g/mol, acrylate equivalent weight: 99 g/mol) as a multifunctional acrylate-based compound, 50 g of PS4040 (manufacturer: Miwon, weight average molecular weight: 1300 g/mol, acrylate equivalent weight: 325, 4-functional, ester-modified) as a multifunctional acrylate-based compound, 112.5 g of MEK-AC-2140Z (silica sol, manufacturer: Nissan Chemical, diameter: 12 nm, solid content: 40%) as inorganic particles, 2 g of 1184 (manufacturer: Ciba) as a photoinitiator, and 100 g of methyl isobutyl ketone as a solvent were mixed to prepare a coating solution for forming a second hard coating layer.

Preparation Example 2-4

[0101] 50 g of trimethylolpropane triacrylate (manufacturer: Cytec, weight average molecular weight: 296 g/mol, acrylate equivalent weight: 99 g/mol) as a multifunctional acrylate-based compound, 50 g of PS4040 (manufacturer: Miwon, weight average molecular weight: 1300 g/mol, acrylate equivalent weight: 325, 4-functional, ester-modified) as a multifunctional acrylate-based compound, 125 g of MEK-AC-2140Z (silica sol, manufacturer: Nissan Chemical, diameter: 12 nm, solid content: 40%) as inorganic particles, 2 g of 1184 (manufacturer: Ciba) as a photoinitiator, and 100 g of methyl isobutyl ketone as a solvent were mixed to prepare a coating solution for forming a second hard coating layer.

Preparation Example 2-5

[0102] 100 g of pentaerythritol triacrylate (manufacturer: Kyoeisha, weight average molecular weight: 298 g/mol, acrylate equivalent weight: 100 g/mol), 125 g of MEK-AC-2140Z (silica sol, manufacturer: Nissan Chemical, diameter: 12 nm, solid content: 40%) as inorganic particles, 2 g of 1184 (manufacturer: Ciba) as a photoinitiator, and 100 g of methyl isobutyl ketone as a solvent were mixed to prepare a coating solution for forming a second hard coating layer.

Examples and Comparative Examples: Protecting Film for Cover Window of Flexible Display Device

[0103] The coating solution for forming a second hard coating layer described in Table 1 below was applied to one surface of a polyethylene terephthalate film, which is a light-transmitting substrate, in a bar coating method, and dried at 60 C. for 2 minutes under an air atmosphere. A second hard coating layer was prepared by photo-curing under a nitrogen atmosphere with a mercury lamp (quantity of light: 100 mJ/cm.sup.2).

[0104] Thereafter, the coating solution for forming a first hard coating layer described in Table 1 below was applied on the second hard coating layer in a bar coating method, and dried at 60 C. for 2 minutes under an air atmosphere. A first hard coating layer was prepared by photo-curing under a nitrogen atmosphere with a mercury lamp (quantity of light: 200 mJ/cm.sup.2) to prepare a protecting film for a cover window.

[0105] After curing was completed, the thickness of the first hard coat layer, the second hard coat layer and the polyethylene terephthalate film were measured using a digital micrometer, and the results are shown in Table 1 below.

TABLE-US-00001 TABLE 1 Comp. Comp. Comp. Comp. Comp. Comp. Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 1st hard Coating Prep. Prep. Prep. Prep. Prep. Prep. Prep. Prep. Prep. coating solution Ex. 1-1 Ex. 1-1 Ex. 1-2 Ex. 1-1 Ex. 1-3 Ex. 1-4 Ex. 1-1 Ex. 1-1 Ex. 1-1 layer Thickness 2 1.5 3 2 5 2 5 2 2 (m) 2nd hard Coating Prep. Prep. Prep. Prep. Prep. Prep. Prep. Prep. Prep. coating solution Ex. 2-1 Ex. 2-2 Ex. 2-2 Ex. 2-3 Ex. 2-2 Ex. 2-2 Ex. 2-1 Ex. 2-4 Ex. 2-5 layer Thickness 5 6 10 5 5 3 5 5 5 (m) Thickness of light- 75 100 75 75 75 75 75 75 75 75 transmitting substrate (m)

Experimental Examples: Measurement of Physical Properties of Protecting Film for Cover Window of Flexible Display Device

Experimental Example 1: Pencil Hardness

[0106] For the first hard coating layer of each protecting film of Examples and Comparative Examples, a pencil was reciprocated three times at 45 degrees under a load of 750 g using a pencil hardness measuring device according to JIS K5400-5-4, and then the maximum hardness without scratches was confirmed.

Experimental Example 2: Bending Resistance Test

[0107] According to JIS K5600-5-1, each protecting film of Examples and Comparative Examples was wound around cylindrical mandrels of various diameters, and then the minimum diameter at which cracks with a length of 3 mm or more did not occur was measured.

Experimental Example 3: Bending Durability Test

[0108] FIG. 1 schematically shows a method for testing bending durability and bending stability of a protecting film according to an embodiment of the present disclosure.

[0109] Each protecting film of Examples and Comparative Examples was laser-cut to a size of 80140 mm to minimize microcracks in the edge. The laser-cut film was placed on a measuring device, and folded and unfolded at 90 degrees with respect to a bottom surface 100,000 times in a continuous operation at room temperature (at a rate of once per 1.5 seconds) such that a gap between folded parts (inner curvature diameter) was 4 mm with a light-transmitting substrate inside.

[0110] After repeating 10,000 times, the film was removed and observed whether cracks with a length of 3 mm or more occurred. When cracks did not occur, bending 10,000 times and observing whether cracks occurred was repeated again to measure the maximum number of repetitions without cracks. When cracks did not occur until repeated 100,000 times, it was evaluated as good, and when cracks occurred, it was evaluated as bad.

Experimental Example 4: Scratch Resistance Test

[0111] For the hard coating layer formed on the front surface of each protecting film of Examples and Comparative Examples, a steel wool (#0000) with a load of 500 gf was reciprocated 100 times at 30 rpm, and the surface of the hard coating film was measured. When one or less scratch of 1 cm or less was observed with the naked eye, it was evaluated as good, and when more than one scratch was observed, it was evaluated as bad.

Experimental Example 5: Transmittance and Haze

[0112] For each protecting film of Examples and Comparative Examples, the transmittance and the haze were measured using a spectrophotometer (device name: COH-400).

[0113] The measurement results of physical properties for Examples and Comparative Examples are shown in Table 2 below.

TABLE-US-00002 TABLE 2 Comp. Comp. Comp. Comp. Comp. Comp. Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Pencil hardness 2H 2H 2H 2H 2H 2H 2H H 2H 3H Bending 6 5 6 8 12 6 10 4 10 16 resistance (mm) Bending durability Good Good Good Good Bad Good Bad Good Bad Bad Scratch resistance Good Good Good Good Good Bad Good Bad Good Good Transmittance (%) 92.0 92.1 92.0 92.1 92.2 92.0 92.1 92.2 92.1 92.0 Haze (%) 0.3 0.4 0.3 0.3 0.3 0.3 0.4 0.3 0.3 0.3

[0114] As shown in Table 2 above, the protecting films for a cover window of a flexible display device of Examples satisfied sufficient flexibility while exhibiting high hardness, and had excellent scratch resistance and optical properties such as transmittance and haze. In particular, there was almost no damage to the film even by repetitive bending or folding operations. Accordingly, it was confirmed that they could be usefully applied to a bendable, flexible, rollable, or foldable mobile device, a display device, or the like.

[0115] In contrast, the protecting films of Comparative Examples exhibited relatively low scratch resistance, or did not exhibit bending durability enough to be used as a protecting film of a flexible display device, unlike in Examples.

[0116] Specifically, it was confirmed that Comparative Example 1 including only the first hard coating layer, Comparative Example 3 in which the first hard coating layer is thicker than the second hard coating layer, and Comparative Examples 5 and 6 containing more than 45 parts by weight of nano silica in the second hard coating layer based on 100 parts by weight of the binder resin had bending durability insufficient for a protecting film of a flexible display device.

[0117] On the other hand, it was confirmed that Comparative Example 2 containing more than 3 parts by weight of nano silica in the first hard coating layer based on 100 parts by weight of the binder resin and Comparative Example 4 including only the second hard coating layer had low scratch resistance.