KR101883600B1 - Method of manufacturing organic light emitting diode comprising light extraction layer with flexibility - Google Patents

Abstract

The present invention relates to a method of manufacturing an organic light emitting device and an organic light emitting device manufactured by the method, in which the method of manufacturing the organic light emitting device includes the following steps: i) forming a light extraction layer by coating a transparent substrate with a curable solution to which TiO_2 nanoparticles and poly(ethylene glycol) diacrylate are added, and exposing the coated substrate to light; ii) forming a stabilization layer by coating the light extraction layer with a polymer solution containing poly(pyromellitic dianhydride-co-4,4′-oxydianiline); and iii) preparing a metal grid electrode on the stabilization layer. A material that imparts flexibility is added to the light extraction layer in a process of preparing the light extraction layer, so that an organic light emitting device suitable as a material for a flexible display is provided.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method of manufacturing an organic light emitting device including a light extracting layer having flexibility,

The present invention relates to a method of manufacturing an organic light emitting device and an organic light emitting device manufactured thereby, and more particularly, to a method of manufacturing an organic light emitting device capable of imparting flexibility to a light extracting layer, To an organic light emitting device capable of emitting light.

Flexible display is a next generation display that is expected to be applied to various IT products because it is light, does not break easily, is convenient to carry and can design various forms. Accordingly, the commercialization of flexible displays is expected to become a new growth engine for the display industry by greatly expanding the display industry. As a flexible display, OLED is the most popular display, and glass substrates are replaced with plastics, and research on polymer materials instead of fragile low molecular materials is getting popular.

Further, a light extraction technique has been developed as a method of breaking the limit of the material efficiency of the organic light emitting device. Basically, the technique of extracting light that is lost inside the OLED to the outside is called light extraction technology. The light extraction technology is largely classified into external light extraction and internal light extraction technology. External light extraction technology is applied to the outside of the OLED device such as MLA (micro lens array), nano scattering structure, lattice, and concave and convex structure. On the other hand, optimization of a micro cavity by optical thickness control inside the substrate such as waveguide mode and SPP mode, and introduction of nanoparticles or nanostructure between the transparent electrode and the glass substrate, Is called internal light extraction technology.

To date, several studies have been reported to increase the efficiency of the optical extraction layer of flexible organic light emitting devices. Korean Patent Laid-Open Publication No. 10-2016-0123535 relates to a method of manufacturing a flexible transparent substrate and a flexible transparent substrate therefrom, and a method of manufacturing a nanocellulose-based transparent substrate and coating a polymer film to compensate for surface roughness . However, in the above patent, there is a problem that the information of the specific polymer film is insufficient and the electrode test is not performed in using the polymer film as a substrate, so that it is impossible to judge the possibility of use as a substrate.

In addition, D. Riedel and CJ Brabec, Organic Electronics 2016, 32, and 27 disclose a method in which a scattering layer is used as a light extracting layer, a surface roughness is controlled using a planarization layer thereon, It is suitable for a substrate-based flat display, but it is unclear whether it can be applied to a flexible material.

In addition, Z. Xu and J. Peng, Organic Electronics 2017, 44, and 225 disclose a polyimide-based light extraction substrate. A polyimide substrate is patterned on a micro patterned glass substrate, As a method of manufacturing an organic light emitting device, there is an advantage that the process is simplified in that the light extracting structure is integrated into the substrate itself to increase the efficiency of the device, but the device is only usable in a special case and the versatility is low. There is a limit to the lack of stability evaluation.

Korean Patent No. 10-1735445, Korean Patent No. 10-1356105, and Korean Patent Laid-Open No. 10-2013-0116559 disclose a method of manufacturing a light extracting layer of an organic light emitting device. However, No repetitive bending stability, i.e., an effective method for improving flexibility, which is an essential element for application to a device, has been proposed.

Korean Patent Publication No. 10-2016-0123535 Korean Patent Publication No. 10-2013-0116559 Korean Patent No. 10-1735445 Korean Patent No. 10-1356105

D. Riedel and C. J. Brabec, Organic Electronics 2016, 32, 27 Z. Xu and J. Peng, Organic Electronics 2017, 44, 225

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is an object of the present invention to provide a method of manufacturing an organic light emitting device capable of improving the flexibility stability of a light extraction layer by introducing a simple additive into a light extraction layer manufacturing process, And an organic electroluminescent device.

According to an aspect of the present invention, there is provided a method of manufacturing a light emitting device, comprising: i) forming a light extracting layer by coating a curable solution containing TiO ₂ nanoparticles and poly (ethylene glycol) diacrylate on a transparent substrate; ii) forming a poly (pyromellitic dianhydride-co-4,4'-oxydianiline) (PMDA-ODA, poly (pyromellitic dianhydride-co-4,4'-oxydianiline) Coating a polymer solution to form a stabilizing layer; And iii) fabricating a metal grid electrode on the stabilizing layer.

The present invention also provides an organic light emitting device comprising a) a transparent substrate, b) a light extraction layer on a transparent substrate, c) a stabilization layer formed on the light extraction layer, and d) a metal grid electrode formed on the stabilization layer, Wherein the light extracting layer comprises TiO ₂ nanoparticles and poly (ethylene glycol) diacrylate, and the stabilizing layer comprises poly (pyromellitic dianhydride-co-4,4'-oxydianiline) And an organic electroluminescent device.

According to the present invention, it is possible to improve the flexibility of the light extracting layer by adding poly (ethylene glycol) diacrylate to the solution for preparing the light extracting layer, and to coat the polymer having a structure having excellent mechanical strength on the light extracting layer By forming the stabilizing layer, a stable light extraction layer can be produced even in repeated bending. Accordingly, it is possible to provide an organic light emitting device excellent in flexibility stability suitable for use in fields such as flexible displays.

1 is a schematic diagram of an organic light emitting device including a light extracting layer and a stabilizing layer according to an embodiment of the present invention and a comparative example.
2 shows an image of a repetitive bending test applied to the present invention.
FIG. 3A is a graph showing the relative conductivity of the organic light emitting device according to an embodiment of the present invention and a comparative example during a repeated bending test in a single state, and FIG. 3B is a graph showing the relative conductivity in a folded state Fig.

Hereinafter, the present invention will be described in more detail with reference to examples and drawings.

At present, the internal light efficiency of the organic light emitting device is improved by improving the structure and purity of the material, so that the efficiency is almost 100%. However, in the case of external light efficiency, the refractive index of the material, the refractive index of the substrate, and the thickness of the substrate are influenced by theoretically about 20%. Many studies have been conducted to improve the external light efficiency, and as a most efficient method, a scattering layer is emerging as a light extracting layer inside the substrate.

When the inner scattering layer is used as the light extracting layer, the light efficiency of the organic light emitting device can be greatly improved. The principle of extracting light that is totally reflected on the glass surface of the organic light emitting device and can not be extracted to the outside is extracted using TiO ₂ particles having high refractive index. The present invention proposes a method of improving the light efficiency of a flexible organic light emitting device by imparting flexibility to the scattering layer.

Accordingly, in the present invention, poly (ethylene glycol) diacrylate is added to the polyfunctional triacrylate used as a base material of the light extracting layer in an appropriate ratio to impart flexibility to the light extracting layer.

Trimethylolpropane triacrylate (TMPTA), which is a main component of the light extracting layer, and poly (ethyleneglycol) acrylate, which is a substance used as an additive, diacrylate (PEGDA). TMPTA, which is used as a base material of the light extracting layer, is cured through light and heat, has three functional points, and has a rigid structure after curing because the distance between the curing points is short.

Further, a poly (pyromellitic dianhydride-co-4,4'-oxydianiline) [PMDA-4,4'-oxydianiline] which is a high-printability and vapor-depositable polymer is used in order to form a repeated bending- ODA, poly (pyromellitic dianhydride-co-4,4'-oxydianiline)] was selected to prepare a stabilized layer of the light extraction layer. The chemical structure of PMDA-ODA is represented by the following formula (3).

In addition, it is easy to form a thin film on a scattering layer or a glass substrate, and a simple spin coating process is adopted. By controlling the thickness of the thin film, the loss of permeability is minimized and the improvement of surface roughness is maximized. In addition, a silver grid was fabricated on the top of the stabilized layer through ink jet equipment to confirm the process stability. Particularly, in the prior art, repeated bending tests, which can not be confirmed, were carried out to evaluate the stability when the electrodes were produced.

Figure 1 is a schematic diagram of a light extraction layer and a stabilization layer according to the present invention. A PC film with a thickness of 100 μm was used as the substrate, and a light / thermosetting material including TiO ₂ particles having a size of 30 nm and 350 nm was used as the light extraction layer having a thickness of 3 μm. As the stabilizing layer, a polymer was coated to a thickness of about 30 nm and used. A silver grid with a line width of 100 μm was used as the electrode. The additives used in the present invention were added to the light extracting layer, and the optimal structure was developed by varying the contents thereof.

Specifically, the method for manufacturing an organic light emitting diode according to the present invention comprises the steps of: i) coating a curable solution to which TiO ₂ nanoparticles and poly (ethylene glycol) diacrylate are added on a transparent substrate, step; ii) coating a polymer solution containing poly (pyromellitic dianhydride-co-4,4'-oxydianiline) on the light extracting layer to form a stabilizing layer; And iii) fabricating a metal grid electrode on the stabilizing layer.

The transparent substrate used in the present invention may be selected from the group consisting of polycarbonate, polyimide, poly (ether sulfone), poly (ethylene terephthalate), poly (methyl methacrylate), poly (ether ether ketone) Among them, polycarbonate (PC) is preferably transparent, light in weight, good in processability in the form of a film, excellent in thermal stability and dimensional stability, good in mechanical properties and suitable for use as a substrate .

On the other hand, a feature of the present invention is that flexibility is imparted to the light extracting layer by using poly (ethylene glycol) diacrylate (PEGDA) in the step of producing the light extracting layer. To this end, poly (ethylene glycol) diacrylate (PEGDA) is added to the curable solution for forming the light extraction layer, wherein the concentration of poly (ethylene glycol) diacrylate is in the range of from 3 to 7 wt %. If it is more than 3 wt%, the degree of curing of the light extracting layer is reduced.

The main component of the curable solution used in the present invention is trimethylolpropane triacrylate, which can be easily cured by heat or light. In the present invention, the light extracting layer is prepared by exposing the curable solution to a negative photoresist (negative PR) solution. The material was excellent in transparency upon curing and cured in a negative manner for application to organic light emitting devices.

At this time, the photoresist solution is coated and then prebaked at 80 to 120 ° C before exposure, and heat treatment is performed at 100 to 300 ° C after exposure of the photoresist solution. This prebaking can remove the solvent in the photoresist solution and stabilize the surface. In addition, the photocuring process is performed through exposure. In order to increase the degree of curing, heat treatment is performed at 100 to 300 ° C. When the heat treatment is performed at a low temperature, the time is increased to advance the curing.

In addition, particles having a size as from 10 to 1000 nm range of the size of the TiO ₂ nanoparticles, TiO ₂ nanoparticles, that is, two types of TiO ₂ nanoparticles and from 100 to 1000 nm in the range of 10 to 50 nm range used in the present invention As shown in FIG. More specifically, in the present invention, the light extracting layer obtains a light extraction effect by using TiO ₂ nanoparticles as a scattering layer. In this case, the size of the TiO ₂ nanoparticles used for extracting light is in the range of 100 to 1000 nm . When the size of the TiO ₂ nanoparticles is less than 100 nm, it is difficult to be influenced by the scattering effect. When the size of the TiO ₂ nanoparticles is more than 1000 nm, coagulation due to the intergranular attracting force occurs. On the other hand, it is more preferable to use fine TiO ₂ nanoparticles in the range of 10 to 50 nm together for the purpose of controlling the refractive index and for smoothing the surface roughness.

In the present invention, after the production of the light extracting layer is completed on the transparent substrate as described above, a stabilizing layer is formed thereon. The stabilizing layer is formed by coating a polymer solution containing poly (pyromellitic dianhydride-co-4,4'-oxydianiline) (poly (pyromellitic dianhydride-co-4,4'-oxydianiline)). Examples of the method for coating the stabilizing layer usable in the present invention include, but not limited to, spin coating, bar coating, dip coating, brush coating and roll-to-roll process. Do. Among them, the use of a spin coating process has an advantage that a relatively small substrate can be coated with a small amount of a solution. However, if the size of the substrate is large, coating methods of other processes can be used.

On the other hand, the solvent of the polymer solution may be selected from one or more of dimethylacetamide, N-methyl-2-pyrrolidone, and aromatic hydrocarbon solvents. Of these, dimethylacetamide is preferably used. The concentration of the polymer solution is preferably in the range of 3 to 7 wt%, and the thickness of the stabilizing layer is preferably in the range of 20 to 50 nm. In the present invention, the thickness of the stabilizing layer film is also important. If the thickness is excessively thick, the film may have a large influence on the transmittance of the film. If the thickness is less than 3 wt%, the film is too thin, .

After the light extraction layer and the stabilization layer are formed as described above, a metal grid electrode necessary for the organic light emitting device may be formed, for example, an Ag grid electrode may be formed. At this time, the line width of the grid electrode ranges from 50 to 150 mu m, and the interval preferably ranges from 100 to 300 mu m.

In the meantime, the present invention provides an organic light emitting device obtained according to the above manufacturing method, which comprises a) a transparent substrate, b) a light extracting layer on a transparent substrate, c) a stabilizing layer formed on the light extracting layer, and d) An organic electroluminescent device comprising a grid electrode, said light extracting layer comprising TiO ₂ nanoparticles and poly (ethylene glycol) diacrylate, said stabilizing layer comprising poly (pyromellitic dianhydride-co- '-Oxydianiline). FIG. 1 is a schematic view showing the structure of an organic light emitting diode according to the present invention.

As described above, the technique of adding flexibility to poly (ethylene glycol) diacrylate to the light extracting layer according to the present invention and forming a specific polymer stabilized layer can be applied to a light extracting layer of a flexible organic light emitting device , Display and lighting. In addition, it can be applied to electronic devices / smart devices based on various organic / nano semiconductors such as wearable electronic devices and bio devices. It is also applicable to human-friendly devices such as bio-IT convergence technologies such as material parts, modules, circuits, It will have a meaningful ripple effect on the industrial sector.

In addition, it can be applied directly to flexible electronic devices and can be applied as a thin film, which can be a basis for wearable electronic device technology. It can be applied to a variety of applications such as sticky IC chips, displays, medical and environmental monitoring sensors, and so on. It is a process that improves the stability of the flexible-based light extracting layer through a simple process, and it can be applied variously to flexible organic light emitting devices and electronic devices. In particular, it can be applied to next-generation electronic parts-related industries as a base technology that can be applied to a recent issue of Ben Double and flexible organic light emitting devices.

Hereinafter, the present invention will be described in more detail with reference to specific examples. However, the following examples are provided to illustrate the present invention and should not be construed as limiting the scope of the present invention. Each sample was made in triplicate and all measurements were averaged over three samples.

<Comparative Example>

As a comparative example, a light extraction layer was formed on a PC film, and an Ag grid electrode was formed on the top of the light extraction layer using an ink jet apparatus. First, a PC film having a size of 25.4 mm x 25.4 mm was immersed in isopropanol, followed by ultrasonic cleaning for 30 minutes and UV-O ₃ treatment for 10 minutes. TiO ₂ particles having a size of 30 nm and a size of 350 nm were mixed in a negative PR (Ormocomp) and stirred for 24 hours to prepare a solution for preparing a light extraction layer. The light extraction layer solution was spin-coated on the cleaned PC film and prebaked at 100 ° C for 5 minutes. The entire surface of the film was exposed, and heat treatment was performed at 130 캜 for 2 hours. When the light extraction layer is completed, the poly (pyromellitic dianhydride-co-4,4'-oxydianiline) (PMDA-ODA) solution is spin coated as a stabilizing layer at a rate of 4000 rpm for 60 seconds, The solvent was removed over time. Next, an Ag grid electrode is formed in the center of the substrate with a size of 2.54 mm x 10 mm by using an ink jet apparatus on top of the stabilization layer. The line width of the grid is about 100 탆, and the interval is set to 200 탆. The resistance of both ends of the fabricated sample was measured, and the resistance in the bending state and the bending state were measured in real time by a repeated bending tester. The stability of the flux - based optical extraction layer was analyzed by converting the measured resistance to an inverse number to obtain the conductivity and converting it to a relative value based on the reference value before the test.

&Lt; Example 1 >

In Example 1, poly (ethylene glycol) diacrylate (PEGDA) was added to the light extracting layer in a content ratio of 5 wt%. The standard of the weight ratio was a light extraction solution containing TiO ₂ particles having sizes of 30 nm and 350 nm. The optical extraction solution mixed with the additives on the cleaned PC film is spin-coated and pre-baked at 100 ° C for 5 minutes. The entire surface of the film was exposed, and heat treatment was performed at 130 캜 for 2 hours. After the light extraction layer was prepared, a poly (pyromellitic dianhydride-co-4,4'-oxydianiline) (PMDA-ODA) solution was diluted with a solvent (Dimethylacetamide) to 5 wt% , Spin coated at a speed of 4000 rpm for 60 seconds, and the solvent was removed at 130 캜 for 2 hours. Next, an Ag grid electrode having a size of 2.54 mm x 10 mm was formed at the center of the substrate by using an ink jet apparatus on top of the stabilization layer. The line width of the grid is about 100 mu m, and the interval is set to 200 mu m.

The resistance of both ends of the sample was measured, and the resistance in the bending state and the bending state were measured in real time by repeating a bending test machine from 1 to 1000 times. The stability of the flux - based optical extraction layer was analyzed by converting the measured resistance to an inverse number to obtain the conductivity and converting it to a relative value based on the reference value before the test.

&Lt; Example 2 >

In Example 2, PEGDA was added to the light extracting layer at a ratio of 10 wt%. The standard of the weight ratio was a light extraction solution containing TiO ₂ particles having sizes of 30 nm and 350 nm. The light extract solution mixed with the additives on the washed PC film was spin-coated and pre-baked at 100 ° C for 5 minutes. The entire surface of the film was exposed, and heat treatment was performed at 130 캜 for 2 hours. After preparation of the light extracting layer, a poly (pyromellitic dianhydride-co-4,4'-oxydianiline) (PMDA-ODA) solution was spin coated as a stabilizing layer at a speed of 4000 rpm for 60 seconds, Lt; / RTI &gt; for 2 hours. Next, an Ag grid electrode having a size of 2.54 mm x 10 mm was formed at the center of the substrate by using an ink jet apparatus on top of the stabilization layer. The line width of the grid is about 100 mu m, and the interval is set to 200 mu m.

The resistance of both ends of the fabricated sample was measured, and the resistance in the bending state and the bending state were measured in real time by a repeated bending tester. The stability of the flux - based optical extraction layer was analyzed by converting the measured resistance to an inverse number to obtain the conductivity and converting it to a relative value based on the reference value before the test.

&Lt; Example 3 >

In Example 3, PEGDA was added to the light extracting layer at a ratio of 15 wt%. The standard of the weight ratio was a light extraction solution containing TiO2 particles of 30 nm and 350 nm size. The light extract solution mixed with the additives on the washed PC film was spin-coated and pre-baked at 100 ° C for 5 minutes. The entire surface of the film was exposed, and heat treatment was performed at 130 캜 for 2 hours. After preparation of the light extracting layer, a poly (pyromellitic dianhydride-co-4,4'-oxydianiline) (PMDA-ODA) solution was spin-coated as a stabilizing layer at a speed of 4000 rpm for 60 seconds, The solvent was removed for 2 hours. Next, an Ag grid electrode having a size of 2.54 mm x 10 mm was formed at the center of the substrate by using an ink jet apparatus on top of the stabilization layer. The line width of the grid is about 100 mu m, and the interval is set to 200 mu m.

The resistance of both ends of the fabricated sample was measured, and the resistance in the bending state and the bending state were measured in real time by a repeated bending tester. The stability of the flux - based optical extraction layer was analyzed by converting the measured resistance to an inverse number to obtain the conductivity and converting it to a relative value based on the reference value before the test.

<Experimental Example>

Fig. 2 shows an image of a repeated bending test. The specimen was 25.4mm x 25.4mm and the electrode was 10mm x 25.4mm. The radius of curvature was set to 3.2 mm (3.2 R) and a total of 1000 repetitive bending tests were performed. The relative conductivities were compared by measuring the resistance in the union state and the bending state.

FIG. 3A is a graph showing the conductivity of the organic light emitting device manufactured in accordance with the above-described embodiment and the comparative example in the repeated state bending test. Fig. 3B shows the relative conductivity in the folded state during the repeated bending test. Both graphs show the same tendency. It can be confirmed that the stability is improved in Example 1 in which the content of PEGDA is 5 wt%. However, as the content of the additive was increased, the stability was decreased in Examples 2 and 3. It can be said that the diacrylate penetrates into the curing point between the triacrylates and the degree of curing is lowered. Further, as the amount of ethylene glycol is increased, the distance between the curing points increases, and the flexibility is increased in Example 1, but the curing degree is decreased because the distance between Examples 2 and 3 is too long. In FIG. 3A, the relative conductivities after the 1000-time bending test are 0.61, 0.78, 0.63, and 0.50, respectively, and the relative conductivities after the 1000-time bending test are 0.55, 0.74, 0.55, and 0.40, respectively.

Claims (22)

i) forming a light extracting layer by coating a curable solution to which TiO ₂ nanoparticles and poly (ethylene glycol) diacrylate are added on a transparent substrate and exposing the coating;
ii) coating a polymer solution having a concentration of 3 to 7% by weight with poly (pyromellitic dianhydride-co-4,4'-oxydianiline) on the light extracting layer to form a film having a thickness in the range of 20 to 50 nm &Lt; / RTI &gt; And
and iii) fabricating a metal grid electrode on the stabilization layer. The method according to claim 1,
Wherein the transparent substrate is selected from the group consisting of polycarbonate, polyimide, poly (ether sulfone), poly (ethylene terephthalate), poly (methyl methacrylate), poly (etheretherketone) / RTI &gt; The method according to claim 1,
Wherein the concentration of the poly (ethylene glycol) diacrylate is in the range of 3 to 7 wt% based on the curable solution. The method according to claim 1,
Wherein the curable solution comprises trimethylolpropane triacrylate. &Lt; RTI ID = 0.0 &gt; 11. &lt; / RTI &gt; The method according to claim 1,
Wherein the curable solution is a negative photoresist solution. 6. The method of claim 5,
Wherein the photoresist solution is coated and then prebaked at a temperature in a range of 80 to 120 캜 before exposure. 6. The method of claim 5,
Wherein the heat treatment is performed at a temperature in the range of 100 to 300 占 폚 after the exposure of the photoresist solution. The method according to claim 1,
Wherein the size of the TiO ₂ nanoparticles ranges from 10 to 1000 nm. 9. The method of claim 8,
Wherein the TiO ₂ nanoparticles are composed of particles having two sizes ranging from 10 to 50 nm and from 100 to 1000 nm. The method according to claim 1,
Wherein the step of forming the stabilizing layer is performed by spin coating a polymer solution. The method according to claim 1,
Wherein the solvent of the polymer solution is selected from the group consisting of dimethylacetamide, N-methyl-2-pyrrolidone, and aromatic hydrocarbon solvents. delete delete The method according to claim 1,
Wherein the electrode is an Ag grid electrode. The method according to claim 1,
Wherein the line width of the grid electrode ranges from 50 to 150 占 퐉 and the interval ranges from 100 to 300 占 퐉. An organic electroluminescent device comprising a) a transparent substrate, b) a light extraction layer formed on a transparent substrate, c) a stabilization layer formed on the light extraction layer, and d) a metal grid electrode formed on the stabilization layer, Layer comprises TiO ₂ nanoparticles and poly (ethylene glycol) diacrylate, said stabilizing layer comprising poly (pyromellitic dianhydride-co-4,4'-oxydianiline) lt; RTI ID = 0.0 &gt; nm. &lt; / RTI &gt; 17. The method of claim 16,
Wherein the transparent substrate is selected from the group consisting of polycarbonate, polyimide, poly (ether sulfone), poly (ethylene terephthalate), poly (methyl methacrylate), poly (etheretherketone) device. 17. The method of claim 16,
Wherein the size of the TiO ₂ nanoparticles ranges from 10 to 1000 nm. 19. The method of claim 18,
Wherein the TiO ₂ nanoparticles are composed of particles having two sizes ranging from 10 to 50 nm and from 100 to 1000 nm. delete 17. The method of claim 16,
Wherein the electrode is an Ag grid electrode. 17. The method of claim 16,
Wherein the line width of the grid electrode ranges from 50 to 150 mu m and the interval ranges from 100 to 300 mu m.

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