KR102431288B1 - Protection film for foldable display and foldable display device comprising same - Google Patents

Abstract

The present invention relates to a protective film for a foldable display and a foldable display device including the same.

Description

Protective film for foldable display and foldable display device including same

The present invention relates to a protective film for a foldable display and a foldable display device including the same. Specifically, it relates to a protective film for a foldable display having excellent foldability and a foldable display device including the same.

Recently, portable terminals such as wireless terminals, personal digital assistants (PDAs), portable multimedia players (PMPs), and electronic notebooks are trending toward smaller sizes for portability.

However, since the user wants to receive information from various contents such as text information, video, and games through the screen of the portable terminal, the size of the display screen is required to be enlarged or widened. However, since the miniaturization of the portable terminal leads to a reduction in the size of the display screen, there is a limit in satisfying both requirements.

Conventional display devices use an unbreakable display, but in order to overcome the above limitations, a curved display, a curved display, and a foldable display are used. And a rollable display (rollable display) and the like have been developed.

The current commercialization stage is about the mobile field in the form of a bent display, and the mobile field using a foldable display is expected to emerge in earnest. In addition, the development speed of the electric field using pOLED is also dazzling.

When using an existing tablet PC or smartphone, the user attaches a protective substrate to the outermost layer of the display and/or the back of the product to prevent scratches on the product display. As a protective substrate, PET protective film, tempered glass, urethane film, etc. are generally applied.

However, when a PET protective film or a tempered glass protective film is applied to a foldable display, fold marks are generated on the folding surface itself, or the protective film is lifted on the folding surface by repeating folding and unfolding several times. There is a problem that the phenomenon occurs.

Therefore, it is necessary to develop a protective substrate that is used as a protective substrate for a foldable display and does not cause a lifting phenomenon from the display surface even after repeated folding and unfolding several times, and an adhesive for attaching the same to the foldable display.

An object of the present invention is to provide a protective film for a foldable display having excellent foldability and a foldable display device including the same.

According to an aspect of the present invention, the pressure-sensitive adhesive layer; and a protective substrate provided on one side of the pressure-sensitive adhesive layer, wherein the adhesive strength measured at 23° C. and 50 RH% after bonding the opposite side of the side in contact with the protective substrate of the pressure-sensitive adhesive layer to the PI substrate is 30 gf/ inch or more, the protective substrate includes transparent polyimide (CPI) or glass, the thickness of the protective substrate is 50 μm or more and 70 μm or less, and as a result of a 3 mm radius folding test, the protective substrate is damaged or detached There is provided a protective film for a foldable display that is maintained without being damaged.

According to another aspect of the present invention a foldable display; and a protective film for a foldable display according to the present invention provided on one surface of the foldable display, wherein the pressure-sensitive adhesive layer of the protective film for a foldable display and one surface of the foldable display are in contact A device is provided.

In the case of a protective film for a foldable display according to an exemplary embodiment of the present invention, the adhesive strength of the pressure-sensitive adhesive layer and the PI substrate is maintained in a specific range condition, so that even if the foldable display device is folded and unfolded several times, the protective substrate and the subsequent It has a feature that does not cause a lifting phenomenon with the cover window of the foldable display.

In addition, in the case of the protective film for a foldable display according to an exemplary embodiment of the present invention, by maintaining the thickness of the protective substrate in a specific range condition, it is possible to effectively prevent scratches from external impacts of the foldable display device and to protect it at the same time The substrate has particularly excellent durability, has excellent foldability, and has excellent folding durability in which the protective substrate does not come off even when applied to a thin foldable display device.

1 is a view showing a laminated structure of a protective film for a foldable display according to an exemplary embodiment of the present invention.
2 is a view showing a laminated structure of a protective film for a foldable display according to an exemplary embodiment of the present invention.
3 is a diagram illustrating a stacked structure of a device for a foldable display according to an exemplary embodiment of the present invention.
4 is a diagram illustrating one side of a foldable display included in an apparatus for a foldable display according to an exemplary embodiment of the present invention.
5 is a diagram illustrating a foldable display device according to an exemplary embodiment of the present invention.
6 is a diagram illustrating a foldable display device according to an exemplary embodiment of the present invention.

In the present specification, when a part "includes" a certain component, it means that other components may be further included, rather than excluding other components, unless otherwise stated.

Embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those of ordinary skill in the art to which the present invention pertains can easily carry out the present invention. However, the present invention may be embodied in several different forms and is not limited to the embodiments described herein.

Hereinafter, the present invention will be described in more detail.

A protective film for a foldable display according to an embodiment of the present invention includes: an adhesive layer; and a protective substrate provided on one side of the pressure-sensitive adhesive layer, wherein the adhesive strength measured at 23° C. and 50 RH% after bonding the opposite side of the side in contact with the protective substrate of the pressure-sensitive adhesive layer to the PI substrate is 30 gf/ inch or more, the protective substrate includes transparent polyimide (CPI) or glass, the thickness of the protective substrate is 50 μm or more and 70 μm or less, and as a result of a 3 mm radius folding test, the protective substrate is damaged or detached is not maintained and

1 shows a laminated structure of a protective film for a foldable display according to an exemplary embodiment of the present invention, in which a pressure-sensitive adhesive layer 2, a protective substrate 4, and a first hard coating layer 5 are sequentially stacked. It can be seen that the structure has

(1) adhesive layer

In an exemplary embodiment of the present invention, the pressure-sensitive adhesive layer serves as an adhesive means to allow the protective film for a foldable display to be attached to the foldable display.

In an exemplary embodiment of the present invention, the adhesive layer provides a protective film for a foldable display comprising at least one adhesive selected from the group consisting of an acrylic adhesive, a silicone adhesive, a urethane adhesive, and a rubber adhesive.

In an exemplary embodiment of the present invention, the pressure-sensitive adhesive layer may include a silicone-based pressure-sensitive adhesive. In one embodiment of the present invention, the pressure-sensitive adhesive layer is a (meth) acrylate-based resin; And it may include a polymer comprising at least one selected from the group consisting of polysiloxane.

As for the polymer, a product obtained by polymerizing two or more different units is called a polymer, and in the polymer, two or more types of units may be arranged irregularly or regularly.

The polymer is a random polymer in which monomers are mixed with each other without regularity, a block copolymer in which blocks arranged by a certain section are repeated, or an alternating copolymer having a form in which monomers are alternately repeated and polymerized (Alternating polymer) may be present, the acrylate-based resin according to an exemplary embodiment of the present invention; And the polymer comprising at least one selected from the group consisting of polysiloxane may be a random polymer, a block polymer, or an alternating polymer.

In an exemplary embodiment of the present invention, the acrylate-based resin may include a (meth)acrylate-based resin having a weight average molecular weight of 100,000 g/mol to 5 million g/mol.

The weight average molecular weight is one of the average molecular weights for which the molecular weight is not uniform and the molecular weight of a certain polymer material is used as a reference, and is a value obtained by averaging the molecular weight of the molecular species of the component molecular weight of the polymer compound having a molecular weight distribution by weight fraction.

The weight average molecular weight may be measured through Gel Permeation Chromatography (GPC) analysis.

In the present specification, (meth) acrylate is meant to include both acrylate and methacrylate. The (meth)acrylate-based resin may be, for example, a copolymer of a (meth)acrylic acid ester-based monomer and a crosslinkable functional group-containing monomer.

The (meth) acrylic acid ester-based monomer is not particularly limited, but for example, an alkyl (meth) acrylate, and more specifically, as a monomer having an alkyl group having 1 to 12 carbon atoms, pentyl (meth) acrylate, n-butyl (meth) acrylate, ethyl (meth) acrylate, methyl (meth) acrylate, hexyl (meth) acrylate, n-octyl (meth) acrylate, isooctyl (meth) acrylate, 2-ethyl One or two or more of hexyl (meth)acrylate, dodecyl (meth)acrylate, and decyl (meth)acrylate may be included.

The crosslinkable functional group-containing monomer is not particularly limited, but may include, for example, one or two or more of a hydroxyl group-containing monomer, a carboxyl group-containing monomer, and a nitrogen-containing monomer.

Examples of the hydroxyl group-containing compound include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate ) acrylate, 8-hydroxyoctyl (meth)acrylate, 2-hydroxyethylene glycol (meth)acrylate, or 2-hydroxypropylene glycol (meth)acrylate.

Examples of the carboxyl group-containing compound include (meth)acrylic acid, 2-(meth)acryloyloxyacetic acid, 3-(meth)acryloyloxypropyl acid, 4-(meth)acryloyloxybutyric acid, acrylic acid double Sieve, itaconic acid, maleic acid, or maleic anhydride, etc. are mentioned.

Examples of the nitrogen-containing monomer include (meth)acrylonitrile, N-vinyl pyrrolidone or N-vinyl caprolactam.

At least one of vinyl acetate, styrene, and acrylonitrile may be further copolymerized with the (meth)acrylate-based resin from the viewpoint of improving other functionalities such as compatibility.

In an exemplary embodiment of the present invention, the acrylate-based resin may be selected from the group consisting of alkyl (meth)acrylates, hydroxyalkyl acrylates and nitrogen-containing monomers.

The alkyl acrylate and alkyl methacrylate are monomers having an alkyl group having 1 to 12 carbon atoms, pentyl (meth) acrylate, n-butyl (meth) acrylate, ethyl (meth) acrylate, methyl (meth) acrylic rate, hexyl (meth) acrylate, n-octyl (meth) acrylate, isooctyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, dodecyl (meth) acrylate and decyl (meth) acrylate One or more of them may be included.

Examples of the hydroxyalkyl acrylate include 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 4-hydroxybutyl acrylate, 6-hydroxyhexyl acrylate, 8-hydroxyoctyl acrylate, 2 -Hydroxyethylene glycol acrylate, 2-hydroxypropylene glycol acrylate, etc. are mentioned.

Examples of the nitrogen-containing monomer include VP (N-vinyl pyrrolidone, N-vinyl pyrrolidone).

In an exemplary embodiment of the present invention, the polysiloxane has a chain of siloxane bonds (-Si-O bonds), and may include polyorganosiloxane.

In an exemplary embodiment of the present invention, the polysiloxane may be polydimethyl siloxane (PDMS).

In an exemplary embodiment of the present invention, the pressure-sensitive adhesive layer further comprises at least one selected from the group consisting of a crosslinking compound, a dispersant, a silane coupling agent, a photocuring agent, a thermosetting agent, a metal salt, and a tackifier. A protective film is provided for

According to an exemplary embodiment of the present specification, the cross-linkable compound is hexanediol di (meth) acrylate, ethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate having 2 to 14 ethylene groups, trimethyl Allpropane di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, 2-trisacryloyloxymethylethylphthalic acid, propylene group Acidic modifications of propylene glycol di(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, dipentaerythritol penta(meth)acrylate with a number of a compound obtained by esterifying a polyhydric alcohol such as a mixture of pentaerythritol hexa(meth)acrylate (trade name: TO-2348, TO-2349, manufactured by Dong-A Synthetic Corporation of Japan) with α,β-unsaturated carboxylic acid; a compound obtained by adding (meth)acrylic acid to a compound containing a glycidyl group, such as a trimethylolpropane triglycidyl ether acrylic acid adduct and a bisphenol A diglycidyl ether acrylic acid adduct; Ester compound of a compound having a hydroxyl group or an ethylenically unsaturated bond, such as a phthalic acid diester of β-hydroxyethyl (meth)acrylate and a toluene diisocyanate adduct of β-hydroxyethyl (meth)acrylate, and a polyhydric carboxylic acid , or adducts with polyisocyanates; (meth)acrylic acid alkyl esters such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate; and 9,9'-bis[4-(2-acryloyloxyethoxy)phenyl]fluorene, which may include one or more selected from the group consisting of, but not limited to, those known in the art. You can use common ones.

According to an exemplary embodiment of the present specification, the photocuring agent is a triazine-based compound, a biimidazole compound, an acetophenone-based compound, an O-acyloxime-based compound, a thioxanthone-based compound, a phosphine oxide-based compound, a coumarin-based compound, and benzo It may be substituted with one or two or more substituents selected from the group consisting of phenone-based compounds.

Specifically, according to an exemplary embodiment of the present specification, the photocuring agent is 2,4-trichloromethyl-(4'-methoxyphenyl)-6-triazine, 2,4-trichloromethyl-(4'-) Methoxystyryl)-6-triazine, 2,4-trichloromethyl-(piflonyl)-6-triazine, 2,4-trichloromethyl-(3',4'-dimethoxyphenyl)- 6-triazine, 3-{4-[2,4-bis(trichloromethyl)-s-triazin-6-yl]phenylthio}propanoic acid, 2,4-trichloromethyl-(4'-ethyl triazine-based compounds such as biphenyl)-6-triazine or 2,4-trichloromethyl-(4'-methylbiphenyl)-6-triazine; 2,2'-bis(2-chlorophenyl)-4,4',5,5'-tetraphenyl biimidazole or 2,2'-bis(2,3-dichlorophenyl)-4,4',5 biimidazole compounds such as ,5'-tetraphenylbiimidazole; 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, 4-(2-hydroxye Toxy)-phenyl (2-hydroxy)propyl ketone, 1-hydroxycyclohexyl phenylketone, 2,2-dimethoxy-2-phenyl acetophenone, 2-methyl-(4-methylthiophenyl)-2-mol Acetopes such as polyno-1-propan-1-one (Irgacure-907) or 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butan-1-one (Irgacure-369) non-type compounds; O-acyloxime compounds such as Ciba Geigy's Irgacure OXE 01 and Irgacure OXE 02; benzophenone compounds such as 4,4'-bis(dimethylamino)benzophenone or 4,4'-bis(diethylamino)benzophenone; thioxanthone-based compounds such as 2,4-diethyl thioxanthone, 2-chlorothioxanthone, isopropyl thioxanthone or diisopropyl thioxanthone; 2,4,6-trimethylbenzoyl diphenylphosphine oxide, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentyl phosphine oxide or bis(2,6-dichlorobenzoyl)propyl phosphine oxide Phosphine oxide type compounds, such as; 3,3'-carbonylvinyl-7-(diethylamino)coumarin, 3-(2-benzothiazolyl)-7-(diethylamino)coumarin, 3-benzoyl-7-(diethylamino)coumarin; 3-benzoyl-7-methoxy-coumarin or 10,10'-carbonylbis[1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H,11H-Cl] Coumarin-based compounds such as -benzopyrano[6,7,8-ij]-quinolizin-11-one may be used alone or two or more may be mixed, but the present invention is not limited thereto.

In addition, the thermosetting agent may be used known in the art.

According to an exemplary embodiment of the present invention, the metal salt may be a Li-containing inorganic salt, and the Li-containing inorganic salt may be LiTFSI (Bis(trifluoromethane)sulfonimide lithium salt).

In an exemplary embodiment of the present invention, the thickness of the pressure-sensitive adhesive layer may be 5 μm or more and 50 μm or less, and the thickness of the pressure-sensitive adhesive layer is 5 μm or more and 50 μm or less, preferably 10 μm or more and 40 μm or less, more preferably may be 15 μm or more and 30 μm or less.

By adjusting the thickness of the pressure-sensitive adhesive layer within the above range, the adhesive strength of the pressure-sensitive adhesive layer can be adjusted within the range according to the present invention.

In an exemplary embodiment of the present invention, the adhesive force measured at 23° C. and 50 RH% after bonding the opposite side of the pressure-sensitive adhesive layer to the PI substrate opposite the side in contact with the protective substrate is 30 gf/inch or more for a foldable display A protective film is provided.

The adhesive force is a value measured using a texture analyzer (Stable Micro Systems, Inc.) at a 180° angle and a peeling rate of 300 mm/min.

In another exemplary embodiment, the adhesive force measured at 23° C. and 50 RH% after bonding the opposite side of the side in contact with the protective substrate of the pressure-sensitive adhesive layer to the PI substrate is 30 gf/inch or more, preferably 35 gf/inch or more, and more preferably 40 gf/inch or more.

In another exemplary embodiment, the adhesive force measured at 23° C. and 50 RH% after bonding the opposite side of the surface in contact with the protective substrate of the pressure-sensitive adhesive layer to the PI substrate is 500 gf/inch or less, preferably 400 gf/inch or less, more preferably 300 gf/inch or less.

In the case of the protective film for a foldable display according to the present invention, the foldable display device is folded and unfolded several times by bonding the adhesive layer opposite the side in contact with the protective substrate to the PI substrate and maintaining the adhesive strength within the above range conditions. Even when repeated, the adhesive force with the protective substrate can be maintained, so that the lifting phenomenon does not occur, and by having the above range, the folding and unfolding operation of the foldable display device is not limited.

That is, if the adhesive force exceeds the above range after bonding the opposite side of the adhesive layer to the PI substrate, the adhesive layer is transferred to the cover window of the foldable display later, and contamination may occur. In addition, when it is less than the above range, when the foldable display is folded, adhesion with the protective substrate cannot be maintained, so that a lifting phenomenon occurs.

The adhesive force can be designed by adjusting the thickness of the pressure-sensitive adhesive layer and the composition of the pressure-sensitive adhesive layer, and the content of the tackifier included in the pressure-sensitive adhesive layer and the content range of the curing agent can be adjusted to satisfy the adhesive strength of the above range. . Specifically, the cohesive force of the pressure-sensitive adhesive layer, the surface characteristics with the PI substrate, wettability, etc. must be considered, and in general, the adhesive force tends to increase as the thickness increases and the tackifier increases. In consideration of these factors, the adhesive strength with PI may be satisfied within the above range.

(2) protective equipment

In one embodiment of the present invention, the protective substrate may be included in a protective film for a foldable display for the purpose of protecting the foldable display due to excellent durability.

In an exemplary embodiment of the present invention, the protective substrate includes transparent polyimide (CPI) or glass. The protective substrate should have excellent flexibility and transparency, and when it contains transparent polyimide (CPI) or glass, it is possible to provide a protective film for a foldable display excellent in foldability.

In an exemplary embodiment of the present invention, the thickness of the protective substrate may be 50 μm or more and 70 μm or less. In addition, the thickness of the protective substrate may be 50 μm or more and 65 μm or less, preferably 50 μm or more and 60 μm or less, and more preferably 50 μm or more and 55 μm or less.

As the thickness of the protective substrate satisfies the above range, the folding and unfolding operations of the foldable display device are not limited, and the cover window of the foldable display can be protected from external scratches and folded several times. and the protective substrate is not lifted even after repeated unfolding, thereby providing a protective film for a foldable display with excellent durability.

In an exemplary embodiment of the present invention, the protective substrate may be maintained without being damaged or detached as a result of the folding test with a radius of 3 mm, and accordingly, the protective film for a foldable display according to the present invention may also be applied to a thin foldable display.

“Radius 3mm folding test” means that the opposite side of the adhesive layer in contact with the protective substrate is bonded to the PI substrate, then the outer surface becomes the protective substrate and the curvature is 3R (the gap between the protective films is 6 mm). After that, it may refer to a test in which it is left for 1 day and unfolded again to check the appearance. As a result of the 3mm radius folding test, when the adhesion between the PI substrate and the pressure-sensitive adhesive layer is maintained and there is no change in appearance, that is, when the protective substrate is not damaged or detached, the foldability of the protective film for a foldable display may be excellent.

(3) Hard coating layer and release film

In one embodiment of the present invention, the protective substrate may further include a first hard coating layer on the opposite surface of the surface in contact with the pressure-sensitive adhesive layer, and a second hard coating layer is further included between the pressure-sensitive adhesive layer and the protective substrate. can do.

In one embodiment of the present invention, the first hard coating layer or the second hard coating layer has high hardness and excellent scratch resistance, so that it is possible to protect the foldable display from the outside and perform an anti-fingerprint function.

The protective film for a foldable display according to an exemplary embodiment of the present invention may further include a second hard coating layer between the pressure-sensitive adhesive layer and the protective substrate.

2 shows a laminated structure of a protective film for a foldable display according to an exemplary embodiment of the present invention. Specifically, a pressure-sensitive adhesive layer (2), a second hard coating layer (3), a protective substrate (4), and a first hard coating layer It can be confirmed that (5) has a stacked structure in this order.

In one embodiment of the present invention, the first hard coating layer or the second hard coating layer may be used without limitation as long as it is widely used in the art, for example, each may include a cured product of an acrylate resin composition. .

In one embodiment of the present invention, the thickness of the first hard coat layer and the second hard coat layer provides a protective film for a foldable display that is 1 μm or more and 10 μm or less, respectively.

In an exemplary embodiment of the present invention, the thickness of the first hard coating layer may be 1 μm or more and 10 μm or less, and the thickness of the second hard coating layer may be 1 μm or more and 10 μm or less.

In another exemplary embodiment, the thickness of the first hard coating layer and the second hard coating layer is 1 μm or more and 10 μm or less, respectively, preferably 2 μm or more and 8 μm or less, more preferably 3 μm or more and 6 μm or less. can

As the first hard coating layer and the second hard coating layer have the above ranges, it is possible to minimize the occurrence of curl due to different physical properties of the protective substrate and the first and second hard coating layers, and scratch resistance of the protective substrate And it has a characteristic that can secure hardness.

In an exemplary embodiment of the present invention, the pressure-sensitive adhesive layer, the opposite surface of the surface in contact with the protective substrate; Or it provides a protective film for a foldable display that further comprises a release film on the opposite surface of the surface in contact with the protective substrate of the first hard coating layer.

In an exemplary embodiment of the present invention, the pressure-sensitive adhesive layer, the opposite surface of the surface in contact with the protective substrate; and a release film on a surface opposite to the surface of the first hard coating layer in contact with the protective substrate.

The release film is a layer for protecting a very thin pressure-sensitive adhesive layer, and refers to a transparent layer attached to one surface of the pressure-sensitive adhesive layer, and a film excellent in mechanical strength, thermal stability, moisture shielding property, isotropy, etc. can be used. For example, acetate-based, polyester-based, polyethersulfone-based, polycarbonate-based, polyamide-based, polyimide-based, polyolefin-based, cycloolefin-based, polyurethane-based and acrylic resin films such as triacetylcellulose (TAC) may be used, but is not limited thereto if it is a commercially available fluorine-treated release film or a silicone-treated release film.

The release film may be removed later in order to adhere the protective film for the foldable display to the foldable display device.

(4) foldable display device

Another embodiment of the present invention is a foldable display; and a protective film for a foldable display according to an embodiment of the present invention provided on one surface of the foldable display, wherein the adhesive layer of the protective film for the foldable display and the foldable display Provided is a foldable display device in which one side is in contact.

3 is a diagram illustrating a stacked structure of a foldable display device according to an exemplary embodiment of the present invention. Specifically, the foldable display 1, the pressure-sensitive adhesive layer 2, the second hard coating layer 3, the protective substrate 4, and the first hard coating layer 5 have a structure in which the first hard coating layer 5 is sequentially stacked, the foldable display It can be seen that one surface of the foldable display and the pressure-sensitive adhesive layer of the protective film for a foldable display are in contact.

In FIG. 3 , the second hard coating layer 3 may be omitted.

In one embodiment of the present invention, the foldable display includes a flexible substrate; organic light emitting layer; polarizer; and a structure in which a cover window is sequentially stacked, and the pressure-sensitive adhesive layer of the protective film for a foldable display may be provided on a surface opposite to a surface of the cover window in contact with the polarizing plate.

The protective film for a foldable display according to the present invention is for scratching and protecting the cover window of the foldable display, and the protective substrate may be attached to one surface of the cover window through an adhesive layer.

That is, the protective film for a foldable display according to an exemplary embodiment of the present invention may be used to protect a cover window of a foldable display device.

In one embodiment of the present invention, the flexible substrate is TPU, polydimethylsiloxane (PDMS), GLASS, polyethylene terephthalate (PET), polyester, polycarbonate (PC), polyimide (PI), polyethylene naphthalate (PEN), It provides a foldable display device selected from the group consisting of polyether ether ketone (PEEK), polyarylate (PAR), polycylicolefin (PCO), polynorbornene, polyethersulphone (PES), and cycloolefin polymer (COP).

In another exemplary embodiment, the flexible substrate may be polyimide (PI).

The polyimide (PI) may be transparent polyimide (PI).

In an exemplary embodiment of the present invention, a first area having a folded portion on a surface opposite to the surface in contact with the pressure-sensitive adhesive layer of the foldable display; and a second region having a non-folding portion, wherein the first region is disposed in a longitudinal direction of the foldable display.

The longitudinal direction refers to all directions perpendicular to the direction of the stacking thickness of the constituent layers of the foldable display device, and specifically refers to a direction included in one surface of the foldable display of the foldable display device.

4 is a view showing one side of a foldable display included in a foldable display device according to an exemplary embodiment of the present invention. Specifically, as can be seen in FIG. 3 , the first area 10 having a fold portion 10 is the foldable display. It can be seen that the second region 11 is disposed in the longitudinal direction of one surface of the display and has a non-folding portion.

In the case of the foldable display according to the present invention, the second area having the non-folding portion may be divided based on the first area having the folded portion on one surface of the foldable display.

That is, as can be seen in FIGS. 4 to 6 , a first area 10 having a folded portion on one surface of the foldable display is disposed, and a second area 11 having a non-folded portion based on the first area is the first area. It can be placed on either side of the area.

In an exemplary embodiment of the present invention, when the foldable display is folded based on the first area, the edges of the second area are in contact with each other.

That the edges of the second region abut each other may include both of the edge parts being in contact with each other or being adjacent to each other even though the edge parts are not in contact with each other. That is, in the foldable display, the edge portion of the second area may be in contact with each other when folding, or may include all of those located adjacent to each other even if they are not in contact.

In the foldable display according to the present invention, when the first region is folded as a reference, the edges of the second region are in a structure that abuts against each other. Specifically, when the foldable display is folded, the folded inner surface is A flexible substrate of the foldable display may be disposed, and a protective film for a foldable display according to the present disclosure including a cover window may be disposed on an outer surface thereof.

5 and 6 are diagrams illustrating a foldable display device according to an exemplary embodiment of the present invention, and specifically, a diagram illustrating a case in which the foldable display according to the present invention is folded.

Referring to FIG. 5 , when the foldable display device is folded according to the fold portion, it can be seen that the protective film 6 for the foldable display according to the present invention is disposed on the outside. Alternatively, referring to FIG. 6 , when the foldable display device is folded according to the fold portion, it can be seen that the protective film 6 for a foldable display according to the present invention is disposed inside.

That is, when the foldable display device of the present invention is folded, the protective film for the foldable display according to the present invention may be disposed on the inside or the outside.

When the protective film for the foldable display is disposed on the outside according to FIG. 5, the protective substrate needs to be maintained as a result of the 4 mm radius folding test, and according to FIG. 6, when the protective film for the foldable display is disposed on the inside, the radius 3mm folding test results may require that the protective substrate be retained.

In the case of the protective film for a foldable display according to an exemplary embodiment of the present invention, the thickness of the protective substrate is 50 μm or more and 70 μm or less, and the adhesive strength between the opposite side of the side in contact with the protective substrate of the pressure-sensitive adhesive layer and the PI substrate is 30 gf/inch or more at 23° C. and 50 RH%, and in particular, when the foldable display is folded based on the first area, the edges of the second area may be in contact with each other.

Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the art can easily carry out the present invention. However, the present invention may be embodied in several different forms and is not limited to the embodiments described herein.

Hereinafter, embodiments will be described in detail to describe the present invention in detail. However, the embodiments according to the present invention may be modified in various other forms, and the scope of the present invention is not to be construed as being limited to the embodiments described below. The embodiments of the present specification are provided to more completely explain the present invention to those of ordinary skill in the art.

Preparation Example 1_Preparation of adhesive layer

After mixing 0.5 parts of CAT-PL-50T, a catalyst, with Shin-Etsu's adhesive KR3700 compared to KR3700, it was diluted with toluene to make 25% of the solid content. Then, 0.5 parts of CAT-PL-50T, a catalyst, was mixed with Shin-Etsu's adhesive KR3704 compared to KR3700, and then diluted with toluene to make 25% of the solid content. Then, the mixture was stirred so that the mixing ratio of KR3700 and KR3704 was 20:80 and coated on the fluorine release film to a final thickness of 25 μm. And the upper part of the adhesive layer was also laminated with a fluorine release film.

Preparation Example 2_Preparation of adhesive layer

It was prepared in the same manner as in Preparation Example 1, except that it was stirred so that the mixing ratio of KR3700 and KR3704 was 30:70 and coated on the fluorine release film to a final thickness of 25 μm.

Preparation Example 3_Preparation of adhesive layer

It was prepared in the same manner as in Preparation Example 1, except that it was stirred so that the mixing ratio of KR3700 and KR3704 was 60:40 and coated on the fluorine release film to a final thickness of 25 μm.

Preparation 4_Preparation of adhesive

DOW CORNING's adhesive 7651 was prepared by adding 1 part of Syl-Off 7028 as a curing agent and 0.5 parts of Syl-Off 4000 as a catalyst and stirring so that the solid content was 20%.

Examples 1 to 4 and Comparative Examples 1 to 10

After corona treatment on one surface of the protective substrate shown in Table 1, an adhesive layer was formed on the corona-treated surface according to the adhesive layer forming method described in Table 1 below.

In the case of Preparation Examples 1 to 3, one fluorine release film of the prepared pressure-sensitive adhesive layer was removed and lamination was performed on the corona-treated surface of the substrate.

In the case of Preparation Example 4, a pressure-sensitive adhesive layer was formed by coating the substrate to have a final thickness of 3 μm.

Since there is no currently released foldable display, a cover window (PI substrate) of a virtual foldable display is selected, and a protective film for the foldable display is attached thereto to obtain a suitable thickness as a protective substrate and an appropriate adhesive strength as an adhesive. Confirmed.

4R folding evaluation

The protective substrate and one fluorine release film of the laminated adhesive were removed and laminated with a PI substrate (SKC KOLON PI's GF200 50um), which is a virtual cover window. After that, the curvature became 4R (the gap between the protective films was 8 mm), the outer surface was folded to become a protective substrate, left for 1 day, and then unfolded again to confirm the appearance.

3R folding evaluation

The appearance was confirmed by testing in the same manner as in the 4R folding evaluation, except that the curvature became 3R (the gap between the protective films was 6 mm) and the inner surface was folded to become a protective substrate.

If there is no change in the adhesion between the PI substrate and the adhesive layer or the appearance of the protective substrate, “maintenance”, when the protective substrate is folded and plastic deformation occurs and cannot be restored to its original state, “damage”, lifting between the adhesive layer and the PI substrate When this occurred and a bubble or tunnel was generated inside, it was classified as “tally”. In addition, when plastic deformation of the PET protective substrate occurred, it was classified as “PET deformation” and described in Table 1 below.

protective material Adhesive layer formation method adhesion
(gf/in) 4R (1 day) 3R (1 day) Thickness (μm) type Example One 50 CPI Preparation 2 30 maintain maintain 2 70 glass Preparation 3 190 maintain maintain 3 70 CPI Preparation 3 190 maintain maintain 4 70 CPI Preparation 2 30 maintain maintain comparative example One 38 PET Preparation 4 One tally tally 2 38 PET Preparation Example 1 12 maintain PET deformation 3 38 PET Preparation 3 190 maintain PET deformation 4 50 CPI Preparation Example 1 12 maintain tally 5 50 PET Preparation Example 1 12 maintain tally 6 50 PET Preparation 3 190 maintain PET deformation 7 70 glass Preparation Example 1 12 tally tally 8 70 CPI Preparation Example 1 12 maintain tally 9 75 PET Preparation 3 190 maintain PET deformation 10 125 PET Preparation 3 190 maintain PET deformation

In Table 1, CPI is a transparent polyimide substrate, glass is glass, and PET is polyethylene terephthalate.

As can be seen from Table 1, Examples 1 to 4 of Table 1 are protective films for foldable displays according to an exemplary embodiment of the present application, maintaining the adhesive strength of the pressure-sensitive adhesive layer and the PI substrate in a specific range condition, and the protective substrate It was confirmed that even when the foldable display device was folded and unfolded several times by maintaining the thickness of the foldable display in a specific range, there was no lifting phenomenon between the protective substrate adhered with the adhesive layer and the cover window of the foldable display. .

In addition, in the case of the protective film for a foldable display according to an exemplary embodiment of the present application, by maintaining the thickness of the protective substrate in a specific range condition, it is possible to effectively prevent scratches from external impacts of the foldable display device and to protect it at the same time The durability of the substrate is particularly excellent.

In the case of Comparative Examples 1 to 10, as a protective film for a foldable display, when the adhesive layer and the PI substrate do not satisfy the adhesive force range or the thickness range of the protective film is not satisfied, the protective substrate is damaged or detached as a result of folding evaluation was able to confirm that In addition, in the case of Comparative Example 1, when the thickness of the pressure-sensitive adhesive layer was 3 μm, it was confirmed that in this case, similarly, sufficient adhesive force was not expressed and a phenomenon in which the protective substrate was detached occurred. In addition, there was a comparative example in which there was no problem in the 4R folding evaluation result, but all of the 3R folding evaluation results, which are more severe folding conditions, had a problem in that detachment or deformation occurred.

1: Foldable display
2: adhesive layer
3: second hard coating layer
4: protective film
5: first hard coating layer
6: Protective film for foldable display
10: first area
11: second area

Claims (14)

pressure-sensitive adhesive layer; and
a protective substrate provided on one surface of the pressure-sensitive adhesive layer; and
After bonding the opposite surface of the pressure-sensitive adhesive layer to the PI substrate, the adhesive force measured at 23° C. and 50 RH% is 30 gf/inch or more,
The protective substrate includes transparent polyimide (CPI) or glass,
The thickness of the protective substrate is 50 μm or more and 70 μm or less,
As a result of the 3mm radius folding test, the protective substrate is maintained without being damaged or detached,
Protective film for foldable displays.
According to claim 1,
The thickness of the pressure-sensitive adhesive layer is 5 μm or more and 50 μm or less for a foldable display
protective film.
According to claim 1,
The pressure-sensitive adhesive layer is a protective film for a foldable display comprising at least one of an acrylic pressure-sensitive adhesive, a silicone-based pressure-sensitive adhesive, a urethane-based pressure-sensitive adhesive, and a rubber-based pressure-sensitive adhesive.
According to claim 1,
The adhesive layer is a protective film for a foldable display further comprising at least one of a crosslinking compound, a dispersant, a silane coupling agent, a photocuring agent, a thermosetting agent, a metal salt, and a tackifier.
According to claim 1,
The protective film for a foldable display further comprising a first hard coating layer on a surface of the protective substrate opposite to the surface in contact with the pressure-sensitive adhesive layer.
6. The method of claim 5,
The thickness of the first hard coating layer is a protective film for a foldable display of 1 μm or more and 10 μm or less.
According to claim 1,
A protective film for a foldable display further comprising a second hard coating layer between the pressure-sensitive adhesive layer and the protective substrate.
8. The method of claim 7,
The second hard coating layer has a thickness of 1 μm or more and 10 μm or less.
protective film for ray.
6. The method of claim 5,
a surface opposite to the surface of the pressure-sensitive adhesive layer in contact with the protective substrate; Or a protective film for a foldable display further comprising a release film on the surface opposite to the surface of the first hard coating layer in contact with the protective substrate.
foldable display; and
A protective film for a foldable display according to any one of claims 1 to 9, provided on one surface of the foldable display;
The foldable display device of claim 1, wherein the pressure-sensitive adhesive layer of the protective film for the foldable display is in contact with one surface of the foldable display.
11. The method of claim 10,
The foldable display may include a flexible substrate;
organic light emitting layer;
polarizer; and
A cover window; in a sequentially stacked structure,
and the adhesive layer of the protective film for the foldable display is provided on a surface of the cover window opposite to the surface in contact with the polarizing plate.
12. The method of claim 11,
The flexible substrate is TPU, polydimethylsiloxane (PDMS), GLASS, polyethylene terephthalate (PET), polyester, polycarbonate (PC), polyimide (PI), polyethylenenaphthalate (PEN), polyether ether ketone (PEEK), polyarylate (PAR). ), PCO (polycylicolefin), polynorbornene (polynorbornene), PES (polyethersulphone), and COP (cycloolefin polymer) of at least one type of foldable display device.
11. The method of claim 10,
a first area having a folded portion on a surface opposite to the surface in contact with the pressure-sensitive adhesive layer of the foldable display; and a second region having a non-folding portion,
The foldable display device of claim 1, wherein the first area is disposed in a longitudinal direction of the foldable display.
14. The method of claim 13,
When the foldable display is folded based on the first area, edges of the second area are in contact with each other.

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