KR20190063486A - Substrate for flexible display apparatus and flexible display apparatus having the substrate - Google Patents

Abstract

Disclosed is a substrate for a flexible display device which is disposed at a lower portion of a flexible display panel and supports the flexible display panel. A substrate for a flexible display device comprises a first substrate layer, a second substrate layer disposed to face the first substrate layer, and a second substrate layer disposed between the first substrate layer and the second substrate layer and adhering them to form a urethane acrylate oligomer compound, And a restoration layer formed of a polymer compound of a first acrylate monomer compound and a monofunctional second acrylate monomer compound. Such a substrate has a high restoring force and can improve the impact resistance of the flexible display device.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a substrate for a flexible display device and a flexible display device including the substrate,

The present invention relates to a substrate applied to a flexible display device and a flexible display device having the same.

Recently, many researches on flexible display devices have been conducted in terms of portability and space utilization. Such a flexible display device has evolved into a display device which can be simply bent or folded. In such a flexible display device, much research has been conducted on a flexible substrate to replace a conventional glass substrate. In this regard, in Korean Patent No. 10-1748009, a coating film is prepared by applying and curing a coating composition composed of a siloxane resin and a polyfunctional acrylic oligomer on one side of a polymer film, thereby improving the flexibility of the material. However, the technique described in Korean Patent No. 10-1748009 has a problem of low impact resistance due to high crosslinking density due to polyfunctional acrylate.

With respect to impact resistance, Korean Patent No. 10-1519422 discloses a substrate for a display having improved impact resistance by forming a skin layer formed by mixing a polymethyl methacrylate resin and a polycarbonate resin on one surface or both surfaces of a polycarbonate substrate having excellent impact resistance However, when a solvent type coating method other than the melt extrusion method described in the above-mentioned patent is applied, there arises a problem that whitish white whitening occurs after coating.

Japanese Patent Application Laid-Open No. 10-2016-0046949 Japanese Patent Application Laid-Open No. 10-2015-0050785

It is an object of the present invention to provide a substrate for a flexible display device which is produced by using a coating composition which does not cause coating whitening during coating and improves the restoring force of the coating layer, thereby improving impact resistance and foldability.

Another object of the present invention is to provide a flexible display device having the substrate.

A substrate for a flexible display device according to an exemplary embodiment of the present invention may be disposed under the flexible display panel to support the substrate. The substrate for a flexible display device may include a first base layer; A second base layer disposed on the first base layer and supporting the display panel; And a second base layer disposed between the first base layer and the second base layer to bond the first base layer and the second base layer to each other, and the first urethane acrylate oligomer compound, the bifunctional first acrylate monomer compound and the monofunctional second acrylate monomer compound Restoration layer.

In one embodiment, the reconstruction layer may have a reconstruction rate of 50% or more.

In one embodiment, the (meth) acrylate mixture which is a mixture of the first urethane acrylate oligomer compound, the bifunctional first acrylate monomer compound and the monofunctional second acrylate monomer compound has a refractive index of 1.495 or more, The restoration layer may be formed using a composition comprising the (meth) acrylate mixture, a photopolymerization initiator, and a solvent.

In one embodiment, the first urethane acrylate oligomer compound may include a (meth) acrylate oligomer represented by the following formula (1).

[Chemical Formula 1]

Wherein X is an aliphatic hydrocarbon having 12 to 18 carbon atoms, Y is an aromatic hydrocarbon having about 6 to 15 carbon atoms, and R 1 and R 2 may independently represent hydrogen or a methyl group.

For example, the first urethane acrylate oligomer compound may include at least one selected from compounds represented by the following general formulas (3) to (5).

(3)

[Chemical Formula 4]

[Chemical Formula 5]

In one embodiment, the bifunctional first acrylate monomer compound may include a (meth) acrylate monomer represented by the following formula (2).

(2)

In the general formula (2), R 3 and R 4 independently represent hydrogen or a methyl group, and n and m are integers of 0 or more, and the sum (n + m) of n and m is 8 or more and 20 or less.

In one embodiment, the solubility parameter of the solvent may be 11 (cal / cm ³ ) ^(1/2) or less.

In one embodiment, the (meth) acrylate mixture comprises from 35 to 80% by weight, based on the total weight of the first urethane acrylate oligomer compound, from 15 to 60% by weight of the first acrylate monomer compound, And 20% by weight of the second acrylate monomer compound.

In one embodiment, the (meth) acrylate mixture may further comprise a second urethane acrylate oligomer compound having not more than 2 functional groups. In this case, the content of the second urethane acrylate oligomer compound may be 35% by weight or less based on the total weight of the (meth) acrylate mixture.

In one embodiment, the (meth) acrylate mixture may further comprise a third acrylate monomer compound having at least two functional groups. In this case, the content of the third acrylate monomer compound may be 10% by weight or less based on the total weight of the (meth) acrylate mixture.

A flexible display device according to an embodiment of the present invention includes a first substrate layer, a second substrate layer disposed to face the first substrate layer, and a second substrate layer disposed between the first substrate layer and the second substrate layer, A support substrate comprising a restoration layer formed of a polymer compound of a urethane acrylate oligomer compound, a bifunctional first acrylate monomer compound, and a monofunctional second acrylate monomer compound; And a flexible display panel disposed on one of the first base layer and the second base layer.

In one embodiment, the flexible display panel may include an OLED panel, an LCD panel, or an E-paper. For example, the flexible display panel may include a panel substrate disposed on the support substrate and having a thin film transistor, and an organic light emitting layer disposed on the panel substrate and emitting light according to the operation of the thin film transistor .

According to the substrate for a flexible display device and the flexible display device including the substrate of the present invention, since the substrate includes a restoration layer formed of a material having a high restoration ratio, the restoration force of the entire substrate is improved, and as a result, The display panel can be stably supported by repeated deformations or strong external impacts of the flexible display device, so that the durability of the flexible display device can be remarkably improved. Also, since the restoration layer is formed by applying the (meth) acrylate mixture having a refractive index of 1.495 or more, the surface whitening phenomenon occurring during coating can be prevented.

1 is a cross-sectional view illustrating a substrate for a flexible display device according to an embodiment of the present invention.
2 is a cross-sectional view illustrating a flexible display device according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The present invention is capable of various modifications and various forms, and specific embodiments are illustrated in the drawings and described in detail in the text. It is to be understood, however, that the invention is not intended to be limited to the particular forms disclosed, but on the contrary, is intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. Like reference numerals are used for like elements in describing each drawing. In the accompanying drawings, the dimensions of the structures are enlarged to illustrate the present invention in order to clarify the present invention.

The terms first, second, etc. may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as a second component, and similarly, the second component may also be referred to as a first component.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In the present application, the term "comprises" or "having ", etc. is intended to specify that there is a feature, step, operation, element, part or combination thereof described in the specification, , &Quot; an ", " an ", " an "

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries are to be interpreted as having a meaning consistent with the contextual meaning of the related art and are to be interpreted as either ideal or overly formal in the sense of the present application Do not.

1 is a cross-sectional view illustrating a substrate for a flexible display device according to an embodiment of the present invention.

Referring to FIG. 1, a supporting substrate 100 for a flexible display device according to an exemplary embodiment of the present invention may include a first base layer 110, a second base layer 120, and a restoration layer 130. The support substrate 100 is disposed under the flexible display panel such as an OLED panel to support the flexible display panel and protect the flexible display panel from an external impact.

The first base layer 110 may be formed of a polymer material to improve the flexibility of the support substrate 100. For example, the first base layer 110 may be formed of polycarbonate, polyethylene terephthalate, polyethylene naphthalate, polymethylmethacrylate, or the like.

The second base layer 120 may be disposed to face the first base layer 110 and may be formed of the same or different polymer material as the first base layer 110.

In one embodiment, the second substrate layer 120 may have the same strength as the first substrate layer 110 to improve the flexibility of the support substrate 100. In this case, the second base layer 120 may be formed of the same material as the first base layer 110. Alternatively, in another embodiment, the second substrate layer 120 may be formed of a soft material having a lower strength than the first substrate layer 110 to further improve the foldability of the support substrate 100 have. In this case, the second base layer 120 may be formed of, for example, a silicone resin, a urethane resin, or the like.

The restoration layer 130 may be disposed between the first base layer 110 and the second base layer 120 and may bond the first base layer 110 and the second base layer 120 have. The restoration layer 130 may be formed of a material having a high recovery ratio to improve the impact resistance of the support substrate 100.

In one embodiment of the present invention, the restoration layer 130 may be formed of a polymer compound of a first urethane acrylate oligomer compound, a bifunctional first acrylate monomer compound, and a monofunctional second acrylate monomer compound. The first urethane acrylate oligomer compound and the first acrylate monomer compound may suppress the restoring force of the restoration layer 130 and the whitening phenomenon during coating and the second acrylate monomer compound may prevent the restoration of the restoration layer 130, , That is, a composition comprising the first urethane acrylate oligomer compound, the first acrylate monomer compound and the second acrylate monomer compound may be lowered to improve workability and moldability .

In one embodiment, the first urethane acrylate oligomer compound may have a structure represented by the following formula (1).

[Chemical Formula 1]

In Formula 1, X may be an aliphatic hydrocarbon having about 12 to 18 carbon atoms, Y may be an aromatic hydrocarbon having about 6 to 15 carbon atoms, and R1 and R2 may be independently hydrogen or a methyl group.

The first acrylate monomer chemistry may have the chemical structure of Formula 2 below.

(2)

In the general formula (2), R 3 and R 4 may independently be hydrogen or a methyl group, and n and m are each an integer of 0 or more, and the sum of n and m may be 8 or more and 20 or less.

In one embodiment, the first urethane acrylate oligomer compound may be formed by polymerizing a bifunctional isocyanate compound containing an aromatic hydrocarbon and an acrylate compound having at least one hydroxy group in the molecule. In this case, the method of polymerizing the bifunctional isocyanate compound containing an aromatic hydrocarbon and the acrylate compound having at least one hydroxy group in the molecule is not particularly limited. For example, they may be any polymerization reaction, block polymerization Reaction, graft polymerization or the like.

The bifunctional isocyanate compound containing the aromatic hydrocarbon may be at least one selected from the group consisting of 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, diphenylmethane diisocyanate, 1,5-naphthalene diisocyanate, xylene diisocyanate, m -Tetramethyl xylene diisocyanate, p-tetramethyl xylene diisocyanate, and trimethylene propanol adduct toluene diisocyanate, and at least one acrylate having at least one hydroxyl group in the molecule The compound is at least one compound selected from the group consisting of hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyisopropylacrylate, hydroxybutyl acrylate, hydroxypentyl acrylate, hydroxyhexyl acrylate, hydroxybutyl vinyl ether, Hydroxyacrylate and cap < RTI ID = 0.0 > It may include one or more selected from the group consisting of a lactone ring-opened hydroxy acrylate.

For example, the first urethane acrylate oligomer compound may include at least one selected from compounds represented by the following general formulas (3) to (5).

(3)

[Chemical Formula 4]

[Chemical Formula 5]

The compound of formula (3) can be synthesized, for example, by reacting 2,4-toluene diisocyanate with caprolactone acrylate. The compound of formula (4) can be synthesized, for example, by reacting 2,4-toluene diisocyanate Polyethylene glycol acrylate, and the compound of formula (5) can be synthesized by, for example, reacting 2,4-toluene diisocyanate with polypropylene glycol acrylate.

The bifunctional first acrylate monomeric compound may include bisphenol A diacrylate containing about 8 to 20 ethylene oxides. For example, the bifunctional first acrylate monomeric compound may comprise a single bisphenol A diacrylate or may comprise a plurality of bisphenol A diacrylates containing different numbers of ethylene oxide.

The type of the monofunctional second acrylate monomer compound is not limited as long as it is a (meth) acrylate monomer having a monofunctional group capable of photopolymerization known in the art.

Meanwhile, in an embodiment of the present invention, the restoration layer 130 may be formed of an acrylate oligomer containing the first urethane acrylate oligomer compound, the bifunctional first acrylate monomer compound, and the monofunctional second acrylate monomer compound And a composition comprising a mixture, a cationic photopolymerization initiator, and a solvent. In addition, the composition may further comprise a second urethane acrylate oligomer compound and a polyfunctional third acrylate monomer compound.

The photoinitiator may include a radical photopolymerization initiator, a cationic photopolymerization initiator, and the like, which may be used alone or in combination of two or more.

As the radical photopolymerization initiator, known radical photopolymerization initiator compounds may be used without limitation and are not particularly limited. For example, the radical photopolymerization initiator may be 1-hydroxycyclohexyl phenyl ketone, 2,2'-dimethoxy-2-phenylacetophenone, xanthone, fluorene, fluorenone, benzaldehyde, anthraquinone, triphenylamine, Carbazole, 3-methylacetophenone, 4-chlorobenzophenone, 4,4'-dimethoxybenzophenone, 4,4'-diaminobenzophenone, mihira ketone, benzoylpropyl ether, benzoin ethyl ether, benzyldimethyl Ketal, 1- (4-isopropylphenyl) -2-hydroxy-2-methylpropan-1-one, 2-hydroxy- 2-isopropylthioxanthone, 2-chlorothioxanthone, 2-methyl-1- [4- (methylthio) phenyl] 1- (4-morpholinophenyl) butan-1-one, 1- [4- (2-hydroxyethoxy) -phenyl ] -2-hydroxy-2-methylpropan-1-one and the like .

As the cationic photopolymerization initiator, known cationic photopolymerization initiator compounds may be used without limitation and are not particularly limited. For example, the cationic photopolymerization initiator may include an onium salt, an organic metal salt, and the like. Specifically, the cationic photopolymerization initiator is selected from the group consisting of a diaryl iodonium salt, a triarylsulfonium salt, an aryldiazonium salt, an arylsulfonium hexafluoroantimonium salt, an arylsulfonium hexafluorophosphate salt, a di Phenyl iodonium hexafluoroantimonium salt, diphenyl iodonium hexafluorophosphate salt, ditolyl iodonium hexafluorophosphate salt, 9- (4-hydroxyethoxyphenyl) cyan sulium hexafluoride, Phosphate salts, iron-arene complexes, and the like. However, since the antimonium salt has environmental pollution problems, the cationic photopolymerization initiator is preferably a hexafluorophosphate salt-based compound.

The solvent improves the applicability of the composition and improves the adhesion between the coating layer and the substrate interface. The solvent to be used in the composition of one embodiment is not limited as long as it is a commonly used organic solvent, but the solubility parameter of the solvent is about 11 (cal / cm ³ ) ^(1/2) or less. In this case, the solubility parameter means a value which is a measure of the solubility. The larger the solubility parameter value is, the higher the polarity of the solvent, and conversely, the lower the value, the lower the polarity of the solvent. The solubility parameter (? _Total ) of each of the constituents described herein is determined by the dispersive coupling specified in the Handbook of Solubility Parameters A User's Handbook (Second Edition), Charles M. Hansen, CRC Press, 2007, page 345-483 to using the solubility parameters (Dispersion, δ _D), polar solubility parameter generated by the combination (polarity, δ _P), the solubility parameter (hydrogen bonding, δ _H) generated by the hydrogen bond was obtained in accordance with equation 1.

[Equation 1]

(? _Total ) ² = (? _D ) ² + (? _P ) ² + (? _H ) ²

When the solubility parameter of the solvent is more than 11 (cal / cm ³ ) ^(1/2) , since the solvent does not sufficiently penetrate and wet the substrate, the adhesion force between the coating layer and the substrate interface becomes weak, and the peeling failure of the coating layer may occur.

The solvent used in the present invention may include at least one selected from an alcohol compound, a ketone compound, a hexane compound, a benzene compound, and the like. The alcohol-based compound may include at least one selected from methanol, ethanol, isopropanol, butanol, methylcellulose, and ethylsorbose. The ketone-based compound may include at least one selected from methyl ethyl ketone, methyl butyl ketone, methyl isobutyl ketone, diethyl ketone, dipropyl ketone, cyclohexanone, and the like. The hexane-based compound may include at least one selected from hexane, heptane, octane, and the like. The benzene-based compound may include at least one selected from benzene, toluene, xylene, and the like

The solvent of the present invention may be a mixed solvent obtained by mixing two or more kinds of solvents. At this time, even if the solubility parameter of the solvent for one kind of mixed solvent exceeds ^{11 (cal / cm 3) (} 1/2) in solubility parameter of the entire mixed solvent is mixed with other solvents ^{11 (cal / cm 3) (} 1 / ²⁾ or less, it can be used in the coating composition of the present invention. For example, in the case of a mixed solvent in which the first solvent and the second solvent are mixed, the solubility parameter of the mixed solvent (隆_{mixed solvent} ) can be calculated from the following equation (2).

The solvent used in the present invention may include at least one selected from an alcohol compound, a ketone compound, a hexane compound, a benzene compound, and the like. The alcohol-based compound may include at least one selected from methanol, ethanol, isopropanol, butanol, methylcellulose, and ethylsorbose. The ketone-based compound may include at least one selected from methyl ethyl ketone, methyl butyl ketone, methyl isobutyl ketone, diethyl ketone, dipropyl ketone, cyclohexanone, and the like. The hexane-based compound may include at least one selected from hexane, heptane, octane, and the like. The benzene-based compound may include at least one selected from benzene, toluene, xylene, and the like

The solvent of the present invention may be a mixed solvent obtained by mixing two or more kinds of solvents. At this time, even if the solubility parameter of the solvent for one kind of mixed solvent exceeds ^{11 (cal / cm 3) (} 1/2) in solubility parameter of the entire mixed solvent is mixed with other solvents ^{11 (cal / cm 3) (} 1 / ²⁾ or less, it can be used in the coating composition of the present invention. For example, in the case of a mixed solvent in which the first solvent and the second solvent are mixed, the solubility parameter of the mixed solvent (隆_{mixed solvent} ) can be calculated from the following equation (2).

[Equation 2]

隆_{mixed solvent} = (X ₁ V ₁隆₁ + X ₂ V ₂隆₂ ) / (X ₁ V ₁ + X ₂ V ₂ )

Wherein X1 and X2 represent the molar fractions of the first and second solvents, V1 and V2 represent the molar volumes of the first and second solvents, respectively, and delta ₁ and delta ₂ are the molar fractions of the first and second solvents, 2 < / RTI > solvent.

Meanwhile, the composition may further include additives commonly used in the art to which the present invention belongs, such as a surfactant, a yellowing inhibitor, and a leveling agent. The content of these additives may be in the range of about 0.1 to 10 parts by weight, but may be variously controlled within a range not deteriorating the physical properties of the present invention.

In one embodiment, the composition may comprise about 35 to 80 weight percent of the first urethane acrylate oligomer compound, based on the total weight of the acrylate mixture. If the content of the first urethane acrylate oligomer compound is less than 35% by weight, the restoration ratio of the restoration layer 130 may be lowered. If the content of the first urethane acrylate oligomer compound exceeds 80% by weight The viscosity of the composition may become excessively high, resulting in a problem that the moldability of the composition is deteriorated.

In one embodiment, the composition may comprise about 15 to 60 weight percent of the bifunctional first acrylate monomer compound, based on the total weight of the acrylate mixture. If the content of the first acrylate monomer compound is less than 15% by weight, the restoration ratio of the restoration layer 130 may be lowered. If the content of the first acrylate monomer compound exceeds 60% by weight There is a problem that the curing shrinkage ratio of the composition is increased and the workability is lowered.

In one embodiment, the composition may comprise about 5 to 20 weight percent of the monofunctional second acrylate monomer compound, based on the total weight of the acrylate mixture. If the content of the second acrylate monomer compound is less than 5% by weight, the viscosity of the composition may be excessively high and the moldability of the composition may be deteriorated. If the content of the second acrylate monomer compound is less than 20% The restoration ratio of the restoration layer 130 may be lowered.

In one embodiment, the composition may include the photoinitiator in an amount of about 1 to 3 wt%, and the solvent in an amount of about 10 to 70 wt%.

On the other hand, when the composition further comprises the third acrylate monomer compound having at least two functional groups, the composition contains less than about 10% by weight of the third acrylate monomer compound based on the total weight of the acrylate mixture can do.

In one embodiment of the present invention, the composition may further comprise a second urethane acrylate oligomer compound having not more than 2 functional groups. In this case, the composition may comprise up to about 35 weight percent of the second urethane acrylate oligomer compound, based on the total weight of the acrylate mixture.

2A and 2B, the flexible display panel may be arranged to be supported by the first base layer 110 or to be supported by the second base layer 130 .

2A and 2B are cross-sectional views illustrating a flexible display device according to an embodiment of the present invention.

Referring to FIGS. 2A and 2B, a flexible display device 1000 according to an embodiment of the present invention includes a support substrate 1100 and a display panel 1200.

The support substrate 1100 may include a first base layer 1110, a second base layer 1120, and a restoration layer 1130. Since the supporting substrate 1100 is substantially the same as the substrate 100 for a flexible display device described with reference to FIG. 1, a detailed description thereof will be omitted.

The flexible display panel 1200 may be disposed on the support substrate 1100. In one embodiment, the flexible display panel 1200 may be disposed on the second base layer 1120 of the support substrate 1100, as shown in FIG. 2A. 2B, the flexible display panel 1200 may be disposed on the first base layer 1110 of the supporting substrate 1100. In this case,

The type of the flexible display panel 1200 is not particularly limited as long as it has a flexible characteristic. For example, the flexible display panel 1200 may include an OLED panel, an LCD panel, an E-paper, and the like.

For convenience of explanation, the flexible display panel 1200 is an OLED panel. The flexible display panel 1200 includes a panel substrate 1210 disposed on the first base layer 1110 or the second base layer 1120 of the supporting substrate 1100 and having a thin film transistor TFT, An organic light emitting layer 1220 disposed on the substrate 1210 and emitting light according to the operation of the thin film transistor and a protective layer 1230 disposed on the organic light emitting layer 1220 and protecting the organic light emitting layer 1220 can do. The flexible display panel 1200 may further include a sealing film and an optical film disposed between the organic light emitting layer 1220 and the passivation layer 1230.

According to the substrate for a flexible display device of the present invention and the flexible display device including the flexible substrate, the substrate may include a restoration layer formed of a material having a high restoring force and may be repeatedly deformed or subjected to strong external shocks such as rolling, folding, The display panel can be stably supported, so that the durability of the flexible display device can be remarkably improved.

Hereinafter, preferred embodiments of the present invention and comparative examples compared with them will be described. However, the following embodiments are only a few embodiments of the present invention, and the present invention should not be construed as being limited to the following embodiments.

[ Urethane acrylate  Synthesis of Oligomer Compound]

≪ Synthesis Example 1: Oligomer 1 >

, 100 parts by weight of 2,4-toluene diisocyanate (Sigma Aldrich), 416 parts by weight of caprolactone acrylate (M100, available from Miwon Specialty Chemicals), 0.5 part by weight of dibutyltin dilaurate (Sigma Aldrich) And 0.2 part by weight of 4-methoxyphenol (Sigma Aldrich), which is an inhibitor, were mixed and stirred at 80 for 6 hours to synthesize a urethane acrylate oligomer compound of the formula (3).

≪ Synthesis Example 2: Oligomer 2 >

100 parts by weight of 2,4-toluene diisocyanate (Sigma Aldrich), 453 parts by weight of polyethylene glycol acrylate (Sigma Aldrich) having a weight average molecular weight of 375, 0.5 part by weight of dibutyltin dilaurate as a reaction catalyst (Sigma Aldrich) And 0.2 part by weight of 4-methoxyphenol (Sigma Aldrich) as a polymerization inhibitor were mixed and stirred at 80 for 6 hours to synthesize a urethane acrylate oligomer compound of the formula (4).

≪ Synthesis Example 3: Oligomer 3 >

100 parts by weight of 2,4-toluene diisocyanate (Sigma Aldrich), 574 parts by weight of polypropylene glycol acrylate (Sigma Aldrich) having a weight average molecular weight of 475, 0.6 parts by weight of dibutyltin dilaurate (Sigma Aldrich) And 0.3 part by weight of 4-methoxyphenol (Sigma Aldrich) as a polymerization inhibitor were mixed and stirred at 80 for 6 hours to synthesize a urethane acrylate oligomer compound of the formula (5).

[ Acrylate  Preparation of the mixture]

Acrylate mixtures having the compositions shown in Tables 1 to 5 below were prepared.

Acrylate mixture composition Mixture 1
(weight %) Mixture 2
(weight %) Mixture 3
(weight %) Mixture 4
(weight %) Mixture 5
(weight %) Urethane acrylate
Oligomer Oligomer 1 35 35 45 45 60 Bifunctional acrylate
Monomer D080 60 45 50 35 35 Monofunctional acrylate
Monomer HEA 5 20 5 20 5 M1140 0 0 0 0 0 Total 100 100 100 100 100 Refractive index 1.511 1.501 1.509 1.499 1.506

Acrylate mixture composition Mixture 6
(weight %) Mixture 7
(weight %) Mixture 8
(weight %) Mixture 9
(weight %) Mixture 10
(weight %) Urethane acrylate
Oligomer Oligomer 1 60 70 80 0 0 Oligomer 2 0 0 0 35 0 Oligomer 3 0 0 0 35 Bifunctional acrylate
Monomer D080 20 25 15 60 60 Monofunctional acrylate
Monomer HEA 20 5 5 5 5 Total 100 100 100 100 100 Refractive index 1.496 1.505 1.503 1.511 1.507

Acrylate mixture composition Mixture 11
(weight %) Mixture 12
(weight %) Mixture 13
(weight %) Mixture 14
(weight %) Mixture 15
(weight %) Urethane acrylate
Oligomer Oligomer 1 35 35 35 35 35 PU210 0 0 0 35 35 Bifunctional acrylate
Monomer D080 0 0 60 15 15 M2100 60 0 0 0 0 M2200 0 60 0 0 0 M240 0 10 Polyfunctional acrylate
Monomer M600 0 0 0 10 0 Monofunctional acrylate
Monomer HEA 5 5 0 5 5 M1140 0 0 5 0 0 Total 100 100 100 100 100 Refractive index 1.508 1.499 1.513 1.496 1.501

Acrylate mixture composition Mixture 16
(weight %) Mixture 17
(weight %) Mixture 18
(weight %) Mixture 19
(weight %) Mixture 20
(weight %) Urethane acrylate
Oligomer Oligomer 1 30 35 0 0 0 PU210 0 0 80 0 0 PU610 0 0 0 80 0 SUO-7301 0 0 0 0 80 Bifunctional acrylate
Monomer D080 65 40 15 15 15 Monofunctional acrylate
Monomer HEA 5 25 5 5 5 Total 100 100 100 100 100 Refractive index 1.513 1.497 1.491 1.497 1.483

Acrylate mixture composition mixture
21
(weight %) Mixture 22
(weight %) mixture
23
(weight %) Mixture 24
(weight %) Mixture 25
(weight %) Mixture 26
(weight %) Urethane acrylate oligomer Oligomer 1 0 0 80 80 80 35 PU210 0 80 0 0 0 40 SUO-7620 80 0 0 0 0 0 Bifunctional acrylate monomer D080 15 0 0 0 0 15 M200 0 15 0 15 0 0 Polyfunctional acrylate monomer M600 0 0 0 0 15 0 Monofunctional acrylate monomer HEA 5 5 5 5 5 10 Total 100 100 85 100 100 100 Refractive index 1.494 1.480 1.521 1.492 1.496 1.493

In Table 1 to Table 5, bifunctional urethane acrylate (SUI-7301), bifunctional urethane acrylate (Shinat TAN Corporation) and 'PU610' are hexafunctional urethane acrylate 'D080', 'M2100', 'M2200', and 'M240' are bisphenol A (ethylene oxide) having a number of ethylene oxide of 8, and 'SUO-7620' is a hexafunctional urethane acrylate Bisphenol Aethoxylate diacrylate (manufactured by Miwon Specialty Chemicals) having an ethylene oxide number of 10, bisphenol Aethoxylate diacrylate having an ethylene oxide number of 20 (manufactured by Miwon Specialty Chemicals) , Bisphenol Aethoxylate diacrylate (manufactured by Miwon Specialty Chemicals) having an ethylene oxide number of 4, and 'M200' represents 1,6-hexadiol diacrylate (manufactured by Miwon Specialty Chemicals) M600 'represents dipentaerythritol hexaacrylate (manufactured by Miwon Specialty Chemicals). 'HEA' represents 2-hydroxyethyl acrylate (Japanese Catalysts) and 'M1140' represents isobornyl acrylate (manufactured by Miwon Specialty Chemicals).

[Preparation of composition]

The acrylate mixtures 1 to 26 were used to prepare coating compositions 1 to 34 having the following composition.

Furtherance Crude composition 1
(weight%) Crude composition 2
(weight%) Crude composition 3
(weight%) Crude composition 4
(weight%) Crude composition 5
(weight%) Crude composition 6
(weight%) Crude composition 7
(weight%) Acrylate mixture Mixture 1 78 0 0 0 0 0 0 Mixture 2 0 78 0 0 0 0 0 Mixture 3 0 0 78 0 0 0 0 Mixture 4 0 0 0 78 0 0 0 Mixture 5 0 0 0 0 78 0 0 Mixture 6 0 0 0 0 0 78 0 Mixture 7 0 0 0 0 0 0 78 Photoinitiator Irgacure
819 2 2 2 2 2 2 2 solvent PGME 20 20 20 20 20 20 20 all 100 100 100 100 100 100 100

Furtherance Composition 8
(weight%) Composition 9
(weight%) Composition 10
(weight%) Composition 11
(weight%) Composition 12
(weight%) Composition 13
(weight%) Composition 14
(weight%) Acrylate
mixture Mixture 8 78 0 0 0 0 0 0 Mixture 9 0 78 0 0 0 0 0 Mixture 10 0 0 78 0 0 0 0 Mixture 11 0 0 0 78 0 0 0 Mixture 12 0 0 0 0 78 0 0 Mixture 13 0 0 0 0 0 78 0 Mixture 14 0 0 0 0 0 0 78 Photoinitiator Irgacure
819 2 2 2 2 2 2 2 solvent PGME 20 20 20 20 20 20 20 all 100 100 100 100 100 100 100

Furtherance Composition 15
(weight%) Composition 16
(weight%) Composition 17
(weight%) Composition 18
(weight%) Composition 19
(weight%) Composition 20
(weight%) Composition 21
(weight%) Acrylate mixture Mixture 8 0 78 78 78 78 78 0 Mixture 15 78 0 0 0 0 0 0 Mixture 16 0 0 0 0 0 0 78 Photoinitiator Irgacure
819 2 2 2 2 2 2 2 solvent PGME 20 0 0 0 16 8 20 n-BA 0 20 0 0 0 0 0 EA 0 0 20 0 0 0 0 MEK 0 0 0 20 0 0 0 IPA 0 0 0 0 4 12 0 all 100 100 100 100 100 100 100

Furtherance Composition 22
(weight%) Composition 23
(weight%) Composition 24
(weight%) Composition 25
(weight%) Composition 26
(weight%) Composition 27
(weight%) Composition 28
(weight%) Acrylate mixture Mixture 17 78 0 0 0 0 0 0 Mixture 18 0 78 0 0 0 0 0 Mixture 19 0 0 78 0 0 0 0 Mixture 20 0 0 0 78 0 0 0 Mixture 21 0 0 0 0 78 0 0 Mixture 22 0 0 0 0 0 78 0 Mixture 23 0 0 0 0 0 0 78 Photoinitiator Irgacure
819 2 2 2 2 2 2 2 solvent PGME 20 20 20 20 20 20 20 all 100 100 100 100 100 100 100

Furtherance Composition 29
(weight%) Composition 30
(weight%) Composition 31
(weight%) Composition 32
(weight%) Composition 33
(weight%) Composition 34
(weight%) Acrylate mixture Mixture 8 0 0 0 78 78 0 Mixture 22 0 0 0 0 0 78 Mixture 24 78 0 0 0 0 0 Mixture 25 0 78 0 0 0 0 Mixture 26 0 0 78 0 0 0 Photoinitiator Irgacure
819 2 2 2 2 2 2 solvent PGME 20 20 20 4 0 4 IPA 0 0 0 16 20 16 all 100 100 100 100 100 100

In Table 6 to Table 10, 'Irgacure 819' represents bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide (BASF Corp.), 'PGME' represents propylene glycol monomethyl ether , 'n-BA' is n-butyl acetate (ocia aisa), 'EA' is ethyl acetate (ocia aisa), 'MEK' is methyl ethyl ketone (ocia aisa), 'IPA' is isopropyl alcohol Aisara).

[ Example  1 to 20 composite films and Comparative Example  1 to 14 composite films]

≪ Preparation of composite film &

Composite films of Examples 1 to 20 were prepared using Compositions 1 to 20 of the compositions shown in Tables 6 to 10 and Composite Films of Comparative Examples 1 to 14 were prepared using Compositions 21 to 34, Whitening, impact resistance, adhesion, and folding properties were evaluated.

Each of the composite films was coated on one surface of a 50 μm polycarbonate film and dried at 80 ° C. for 2 minutes. The primed silicone film was laminated on the coated surface, laminated, and then developed to a thickness of 1000 mJ / The coating composition was cured by UV irradiation to produce a composite film. As the polycarbonate film, a product of Shin-Heung Chemical Co., Ltd. was used, and as the silicon film, a product of Silicon Valley Co. was used.

The whiteness evaluation was made by visually observing the occurrence of a white spot phenomenon when the sheet was observed under the three-wavelength stand after the composite film was produced. When white spot phenomenon is not recognized, '' is indicated. When white spot spot phenomenon is partially observed, 'X' is indicated.

The impact resistance was evaluated by measuring the maximum height at which the composite film did not cause external deformation when dropping 22 g of iron balls on the surface of the composite film.

The adhesive force was obtained by forming 100 squares in each of the composite films by drawing 11 straight lines in the horizontal and vertical directions at intervals of 1 mm and then performing the peeling test three times using a tape (3M). As a result, Is 10 or less, and when it is more than 10, it is indicated as 'X'.

The folding property is a result of folding the composite film to a size of 2 cm in width and 15 cm in length and folding it 200,000 folds using a U-shape Folding Tester (DLDMLH-FS, Yuasa System Co., Ltd.) When there is no trace, '' is indicated. When there is a crack or folding trace, 'X' is indicated. In the folding test, the folding radius of curvature was 2.5 mm and the folding speed was set to 1 rotation per minute (60 Hz).

On the other hand, a coating layer was formed on the PMMA / PC substrate (ShineTech, AW20, Wavelock Advanced Technology Co.) using the above compositions 1 to 34, and then the recovery rate of the coating layer was evaluated. Specifically, the coating layer was coated on one surface of a PMMA / PC substrate having a thickness of 1000 탆 and dried at 80 for 2 minutes. Then, a releasing film was bonded to the coated surface, lamination was performed and then 1000 mJ / Lt; RTI ID = 0.0 > UV < / RTI > At this time, all the coating layers were formed to have a thickness of 20 mu m.

The restoration ratio of the coating layer was evaluated by measuring the indentation depth of the coating layer after removing the release film from the coating layer using a nanoindent (NanoTest, Micromaterials Inc.). Specifically, the indentation depth and the indentation load at the time of indentation loading of the nanoindenter were removed, and the indentation depth after the coating layer was restored was measured. The restoration ratio was calculated using the following Equation 3, and the results are shown in Tables 11 to 15 . The applied nanoindenter tip was of the Berkovich type, with a maximum load of 500 mN and an indentation depth of 7000 nm. The indentation load time was set to 15 seconds and the indentation load removal time was set to 15 seconds.

[Equation 3]

rescue Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Composite film Substrate 1
(thickness) Si film
(50 탆) Si film
(50 탆) Si film
(50 탆) Si film
(50 탆) Si film
(50 탆) Si film
(50 탆) Si film
(50 탆) Coating layer
(thickness) Composition 1
(25 탆) Composition 2
(25 탆) Composition 3
(25 탆) Composition 4
(25 탆) Composition 5
(25 탆) Composition 6
(25 탆) Composition 7
(25 탆) Substrate 2
(thickness) PC film
(50 탆) PC film
(50 탆) PC film
(50 탆) PC film
(50 탆) PC film
(50 탆) PC film
(50 탆) PC film
(50 탆) Solvent S.P 9.99 9.99 9.99 9.99 9.99 9.99 9.99 Acrylate
Refractive index of mixture 1.511 1.501 1.509 1.499 1.506 1.496 1.505 Coated whitening ○ ○ ○ ○ ○ ○ ○ Adhesion ○ ○ ○ ○ ○ ○ ○ Coating layer restoration ratio (%) 57.1 51.3 71.6 67.1 89.1 80.3 93.9 Impact resistance (mm) 400 400 450 450 500 450 500 Folding ability ○ ○ ○ ○ ○ ○ ○

rescue Example 8 Example 9 Example 10 Example 11 Example 12 Example 13 Example 14 Composite film Substrate 1
(thickness) Si film
(50 탆) Si film
(50 탆) Si film
(50 탆) Si film
(50 탆) Si film
(50 탆) Si film
(50 탆) Si film
(50 탆) Coating layer
(thickness) Composition 8
(25 탆) Composition 9
(25 탆) Composition 10
(25 탆) Composition 11
(25 탆) Composition 12
(25 탆) Composition 13
(25 탆) Composition 14
(25 탆) Substrate 2
(thickness) PC film
(50 탆) PC film
(50 탆) PC film
(50 탆) PC film
(50 탆) PC film
(50 탆) PC film
(50 탆) PC film
(50 탆) Solvent S.P 9.99 9.99 9.99 9.99 9.99 9.99 9.99 Acrylate
Refractive index of mixture 1.503 1.511 1.507 1.508 1.499 1.513 1.496 Coated whitening ○ ○ ○ ○ ○ ○ ○ Adhesion ○ ○ ○ ○ ○ ○ ○ Coating layer restoration ratio (%) 96.5 60.9 52.6 61.7 64.7 56.8 51.8 Impact resistance 500 400 400 400 450 400 400 Folding ability ○ ○ ○ ○ ○ ○ ○

rescue Example 15 Example 16 Example 17 Example 18 Example 19 Example 20 Composite film Substrate 1
(thickness) Si film
(50 탆) Si film
(50 탆) Si film
(50 탆) Si film
(50 탆) Si film
(50 탆) Si film
(50 탆) Coating layer
(thickness) Composition 15
(25 탆) Composition 16
(25 탆) Composition 17
(25 탆) Composition 18
(25 탆) Composition 19
(25 탆) Composition 20
(25 탆) Substrate 2
(thickness) PC film
(50 탆) PC film
(50 탆) PC film
(50 탆) PC film
(50 탆) PC film
(50 탆) PC film
(50 탆) Solvent S.P 9.99 8.55 8.88 9.3 10.34 10.97 Acrylate
Refractive index of mixture 1.501 1.503 1.503 1.503 1.503 1.503 Coated whitening ○ ○ ○ ○ ○ ○ Adhesion ○ ○ ○ ○ ○ ○ Coating layer restoration ratio (%) 54.6 96.3 95.9 95.7 96.9 97.1 Impact resistance 400 500 500 500 500 500 Folding ability ○ ○ ○ ○ ○ ○

rescue Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Comparative Example 7 Composite film Substrate 1
(thickness) Si film
(50 탆) Si film
(50 탆) Si film
(50 탆) Si film
(50 탆) Si film
(50 탆) Si film
(50 탆) Si film
(50 탆) Coating layer
(thickness) Composition 21
(25 탆) Composition 22
(25 탆) Composition 23
(25 탆) Composition 24
(25 탆) Composition 25
(25 탆) Composition 26
(25 탆) Composition 27
(25 탆) Substrate 2
(thickness) PC film
(50 탆) PC film
(50 탆) PC film
(50 탆) PC film
(50 탆) PC film
(50 탆) PC film
(50 탆) PC film
(50 탆) Solvent S.P 8.88 8.88 8.88 8.88 8.88 8.88 8.88 Acrylate
Refractive index of mixture 1.513 1.497 1.491 1.497 1.483 1.494 1.480 Coated whitening ○ ○ X ○ X X X Adhesion ○ ○ ○ ○ ○ ○ ○ Coating layer restoration ratio (%) 44.3 47.1 37 19.7 39.4 18.9 21.2 Impact resistance 300 350 300 200 300 200 200 Folding ability X X X X X X X

rescue Comparative Example 8 Comparative Example 9 Comparative Example 10 Comparative Example 11 Comparative Example 12 Comparative Example 13 Comparative Example 14 Composite film Substrate 1
(thickness) Si film
(50 탆) Si film
(50 탆) Si film
(50 탆) Si film
(50 탆) Si film
(50 탆) Si film
(50 탆) Si film
(50 탆) Coating layer
(thickness) Composition 28
(25 탆) Composition 29
(25 탆) Composition 30
(25 탆) Composition 31
(25 탆) Composition 32
(25 탆) Composition 33
(25 탆) Composition 34
(25 탆) Substrate 2
(thickness) PC film
(50 탆) PC film
(50 탆) PC film
(50 탆) PC film
(50 탆) PC film
(50 탆) PC film
(50 탆) PC film
(50 탆) Solvent S.P 8.88 8.88 8.88 8.88 11.26 11.53 11.26 Acrylate
Refractive index of mixture 1.521 1.492 1.496 1.493 1.503 1.503 1.480 Coated whitening ○ X ○ X ○ ○ X Adhesion ○ ○ ○ ○ X X X Coating layer restoration ratio (%) 44.5 34.6 32.1 48.2 95.9 96.2 20.9 Impact resistance 350 250 250 300 500 500 200 Folding ability X X X X ○ ○ X

In the above Tables 11 to 15, 'Solvent S.P' is the solubility parameter value of the solvent applied to each composition as the solubility parameter of the solvent, and 'acrylate mixture refractive index' refers to the refractive index of the acrylate mixture Refractive index.

Referring to Tables 11 to 15, it can be confirmed that the composite films of Examples 1 to 20 have remarkably improved impact resistance due to a high restoration ratio of the coating layer, as compared with the composite films of Comparative Examples 1 to 11. In the composite films of Comparative Examples 1 to 11, no cracks or folding marks were observed in the same test in the composite films of Examples 1 to 20, while cracking and folding marks were generated in the folding test as described above. Compared with the composite films of the comparative examples, the composite films of Examples 1 to 20 did not cause whitening of the coating layer while maintaining the adhesion of the coating layer. No whitening of the coating layer occurred after coating.

In the composite film of Comparative Example 1, it was judged that the content of urethane acrylate oligomer 1 was less than 35% and the content of bifunctional acrylate monomer was more than 60% by weight, It was judged that the content of the monofunctional acrylate monomer was more than 20% by weight and that the restoration ratio and the foldability were lowered. In the composite films of Comparative Examples 3 and 5, bifunctional urethane acrylate oligomers different from the structure of the formula , The restoration ratio and the folding property were deteriorated, and the refractive index of the acrylate mixture was less than 1.495, indicating that the whitening occurred. In the composite film of Comparative Examples 4 and 6, since the hexafunctional urethane acrylate oligomer having a structure different from that of the structural formula (1) was applied, the restoration ratio and the folding property were greatly decreased. In the composite film of Comparative Example 7, The bifunctional urethane acrylate oligomer and the bifunctional acrylate monomer having no aromatic hydrocarbon structure different from the structural formula (2) were applied. Thus, the restoration ratio and folding property were lowered and the refractive index of the acrylate mixture was less than 1.495 In the composite film of Comparative Example 8, the bifunctional acrylate monomer having the number of ethylene oxide of 4, which is different from that of the structural formula (2), was applied. In the composite film of Comparative Example 9, since the bifunctional monomer having no aromatic hydrocarbon having a structure different from that of the structural formula (2) was applied, the restoration ratio and the folding property were lowered and the refractive index of the acrylate mixture was less than 1.495, In the composite film of Example 10, it was judged that the bifunctional acrylate monomer and 6-functional acrylate monomer were applied, so that the restoration ratio and the foldability were decreased. In the composite film of Comparative Example 11, the content of PU210 exceeded 35% by weight It is judged that the restoring force and the foldability are decreased. In the composite films of Comparative Examples 12 and 13, the adhesion was deteriorated because a solvent having a solubility parameter exceeding 11 (cal / cm ³ ) ^(1/2) was applied. In the composite film of Comparative Example 14, A bifunctional urethane acrylate having a different structure and a bifunctional monomer having no aromatic hydrocarbon having a structure different from that of the formula ⁽²⁾ and a solvent having a solubility parameter exceeding 11 (cal / cm ³ ) ^(1/2) , Whitening occurred and adhesion was decreased.

According to the present invention, when the restoration layer having a high refractive index is formed between the upper substrate and the lower substrate according to the present invention, the whitening of the coating layer is suppressed and the restoring force of the entire substrate is improved, And the foldability is improved.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the present invention as defined by the following claims. It can be understood that it is possible.

100: Support substrate 110: First substrate layer
120: second base layer 130: restoration layer

Claims (15)

1. A substrate for a flexible display device disposed at a lower portion of a flexible display panel to support the flexible display panel,
A first base layer;
A second base layer disposed to face the first base layer; And
The first base layer and the second base layer are bonded to each other, and the first urethane acrylate oligomer compound, the bifunctional first acrylate monomer compound, and the monofunctional second acrylate monomer compound are restored Layer,
Wherein the flexible display is disposed on one of the first base layer and the second base layer. The method according to claim 1,
Wherein the restoration rate of the restoration layer is 50% or more. The method according to claim 1,
Wherein the refractive index of the (meth) acrylate mixture which is a mixture of the first urethane acrylate oligomer compound, the bifunctional first acrylate monomer compound and the monofunctional second acrylate monomer compound is at least 1.495,
Wherein the restoration layer is formed using a composition comprising the (meth) acrylate mixture, a photopolymerization initiator, and a solvent. The method of claim 3,
Wherein the first urethane acrylate oligomer compound comprises a (meth) acrylate oligomer represented by the following formula (1): < EMI ID =
[Chemical Formula 1]

Wherein X is an aliphatic hydrocarbon having 12 to 18 carbon atoms and Y is an aromatic hydrocarbon having about 6 to 15 carbon atoms and R1 and R2 independently represent hydrogen or a methyl group. 5. The method of claim 4,
Wherein the first urethane acrylate oligomer compound comprises at least one selected from the group consisting of compounds represented by the following formulas (3) to (5):
(3)

[Chemical Formula 4]

[Chemical Formula 5]

The method of claim 3,
Wherein the bifunctional first acrylate monomer compound comprises a (meth) acrylate monomer represented by the following formula (2): < EMI ID =
(2)

In the general formula (2), R 3 and R 4 independently represent hydrogen or a methyl group, and n and m are integers of 0 or more, and the sum (n + m) of n and m is 8 or more and 20 or less. The method of claim 3,
Wherein the solubility parameter of the solvent is 11 (cal / cm ³ ) ^(1/2) or less. The method of claim 3,
Wherein said (meth) acrylate mixture comprises from 35 to 80% by weight of said first urethane acrylate oligomer compound, from 15 to 60% by weight of said first acrylate monomer compound and from 5 to 20% 2 < / RTI > acrylate monomer compound. The method of claim 3,
Wherein the (meth) acrylate mixture further comprises a second urethane acrylate oligomer compound having a functionality of 2 or less. 10. The method of claim 9,
Wherein the content of the second urethane acrylate oligomer compound is not more than 35% by weight based on the total weight of the (meth) acrylate mixture. The method of claim 3,
Wherein the (meth) acrylate mixture further comprises a third acrylate monomer compound having at least two functional groups. 12. The method of claim 11,
Wherein the content of the third acrylate monomer compound is 10 wt% or less based on the total weight of the (meth) acrylate mixture. A first base layer, a second base layer disposed to face the first base layer, and a second base layer disposed between the first base layer and the second base layer and adhering them to form a urethane acrylate oligomer compound, A support substrate comprising a restoration layer formed of a polymer compound of a monomeric monomer compound and a monofunctional second acrylate monomeric compound; And
And a flexible display panel disposed on one of the first base layer and the second base layer. 14. The method of claim 13,
Wherein the flexible display panel includes an OLED panel, an LCD panel, or E-paper. 14. The method of claim 13,
Wherein the flexible display panel includes a panel substrate disposed on the support substrate and having a thin film transistor and an organic light emitting layer disposed on the panel substrate and emitting light according to operation of the thin film transistor, Display device.

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