Composition for graphene ink and method for manufacturing the same

Abstract

The present invention provides a water-based graphene ink composition comprising a single layer of reduced graphene oxide (RGO), wherein the graphene ink composition has dispersibility that disperses in water at a concentration of 5 g / L to 10 g / L, a conductive film, and a method for preparing the water-based graphene ink composition.

Description

Technology Field

[0001] The present invention relates to a graphene ink composition and a method for manufacturing the same. Background Technology

[0002] Graphene is a material attracting attention in various fields, such as electronic devices, sensors, and energy storage devices, due to its excellent electrical and thermal conductivity, flexibility, stability, and abundant resources. In particular, graphene ink is used as a core material for conductive inks and printing technologies by leveraging the unique properties of graphene. These graphene-based inks are suitable for low-cost, mass production technologies such as printed electronics and offer diverse application possibilities, including sensors and circuits.

[0003] However, existing graphene ink manufacturing technologies generally involve the use of organic solvents or require high temperatures and complex processes, leading to problems such as increased production costs and environmental burden. Furthermore, water-based graphene inks have faced difficulties in commercialization due to limited concentration and stability issues. The unstable dispersion and aggregation of graphene layers cause a degradation in electrical performance, making it crucial to develop inks that can be stably dispersed while maintaining high conductivity.

[0004] There is a need for a new system that can solve these problems and improve the sensitivity and accuracy of the ink.

[0005] The background description of the invention is provided to facilitate a better understanding of the present invention. The matters described in the background description should not be construed as an acknowledgment that they exist as prior art. The problem to be solved

[0006] Attempts to resolve the instability of graphene layers and limitations on commercial applications have continued through various studies.

[0007] More specifically, some studies succeeded in obtaining a stable dispersion at 0.1 g / L or less by combining graphitic nanoplatelets with a specific polymer, but it was found that stability could not be maintained at higher concentrations.

[0008] Furthermore, additional research secured graphene ink with improved stability through pH control, but the dispersion concentration was still limited to 0.5 g / L or less, and the newly proposed polymer-based hybrid film was found to have problems with dispersion concentration and uniformity of the graphene layer.

[0009] In other words, subsequent research may fail to fundamentally resolve the cohesion problem and may face technical limitations that remain at the laboratory level.

[0010] The inventors of the present invention sought to solve the major limitations of existing graphene ink technology, particularly the problems of low dispersion stability and aggregation at high concentrations.

[0011] The inventors of the present invention sought to improve the dispersion of water-based graphene inks in particular, and recognized that graphene oxide (GO) could maintain stable dispersion in a single layer without aggregation even at high concentrations by effectively controlling the surface charge of reduced graphene oxide (RGO).

[0012] More specifically, the inventors of the present invention intended to impart strong electrical repulsion to graphene sheets by introducing cationic polymers, and recognized that this approach suppresses the tendency of graphene sheets to aggregate with each other and ensures stability over a wide pH range.

[0013] In addition, the inventors of the present invention were able to confirm that these features prevent the aggregation of the dispersion and maintain stability even in environments with high electrolyte concentrations.

[0014] As a result, the inventors of the present invention developed a water-based graphene ink composition having stable dispersion power even at high concentrations of 5 to 10 g / L or more.

[0015] At this time, the inventors of the present invention were able to confirm that the newly developed graphene ink composition maintains long-term stability even at high concentrations and exhibits excellent dispersion characteristics under various solvent treatments, thereby effectively preventing not only the increase in the concentration of the graphene dispersion but also the aggregation between graphene sheets and the degradation of electrical performance.

[0016] The inventors of the present invention could expect that this would overcome the limitations of existing graphene ink compositions and provide a high-performance graphene ink suitable for commercial use.

[0017] In particular, the inventors of the present invention could expect to simplify existing complex and inefficient manufacturing processes, enable eco-friendly mass production without high-temperature treatment, and thereby expand the potential for commercial application.

[0018] Accordingly, the problem that the present invention aims to solve is to provide a water-based graphene ink composition comprising a single layer of reduced graphene oxide that has stable dispersion power even at high concentrations of 5 to 10 g / L or more.

[0019] The problems of the invention are not limited to those mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the description below. means of solving the problem

[0020] To solve the problem described above, a water-based graphene ink composition comprising a substrate according to one embodiment of the present invention is provided. The graphene ink composition is a water-based graphene ink composition comprising a single layer of reduced graphene oxide (RGO), wherein the graphene ink composition has dispersibility that disperses in water at a concentration of 5 g / L to 10 g / L.

[0021] According to the features of the present invention, the water-based graphene ink composition can maintain dispersion power at pH 1 to pH 14.

[0022] According to another feature of the present invention, the water-based graphene ink composition can maintain dispersion in a solvent environment.

[0023] To solve the problem described above, a conductive film comprising a substrate according to one embodiment of the present invention is provided.

[0024] The conductive film comprises a substrate and a substrate-water-based graphene ink composition.

[0025] According to a feature of the present invention, the conductive film may have a sheet resistance of 1,000 Ω / sq to 10,000 Ω / sq.

[0026] According to another feature of the present invention, the conductive film may have a conductivity of 100 S / m to 1000 S / m.

[0027] According to another feature of the present invention, the conductive film may have an annealing temperature of 100°C or less for conductivity expression.

[0028] To solve the problem described above, a method for preparing a water-based graphene ink composition comprising a substrate according to another embodiment of the present invention is provided.

[0029] The above manufacturing method comprises the steps of: dispersing graphene oxide to obtain dispersed graphene oxide; preparing a polymer solution; adding the dispersed graphene oxide to the polymer solution to obtain a dispersion; adding a reducing agent to the dispersion to obtain reduced graphene oxide (RGO); and redispersing the reduced graphene oxide in water to obtain a water-based graphene ink composition.

[0030] According to a feature of the present invention, the step of adding dispersed graphene oxide may include the step of mixing the dispersed graphene oxide in a polymer solution.

[0031] According to another feature of the present invention, the step of preparing a polymer solution may include the step of preparing a cationic polymer and the step of diluting the cationic polymer in water.

[0032] According to another feature of the present invention, the cationic polymer may be polyethyleneimine (PEI) or diallyl dimethylammonium chloride (PDDA).

[0033] According to another feature of the present invention, the step of adding a reducing agent may include the step of adding a reducing agent to a dispersion to obtain a mixture, the step of placing the mixture in an oil bath, and the step of performing heat treatment to obtain reduced graphene oxide.

[0034] According to another feature of the present invention, the reducing agent may be at least one of hydrazine monohydrate, sodium borohydride, and hydroquinone.

[0035] According to another feature of the present invention, after the step of adding a reducing agent, the method further includes the step of centrifuging the reduced graphene oxide (RGO) so that the residual reducing agent or residual polymer solution is removed from the reduced graphene oxide, and the redispersion step may include the step of redispersing the reduced graphene oxide from which the residual reducing agent or residual polymer solution has been removed in water.

[0036] According to another feature of the present invention, the water-based graphene ink composition may have dispersibility that disperses in water at a concentration of 5 g / L to 10 g / L.

[0037] The present invention will be explained in more detail below through examples. However, since these examples are merely illustrative of the present invention, the scope of the present invention should not be interpreted as being limited by these examples. Effects of the invention

[0038] The present invention can effectively solve the problems of low dispersion stability and aggregation at high concentrations, which are major limitations of existing graphene ink technology.

[0039] In particular, the present invention can provide a water-based graphene ink composition that prevents aggregation between graphene sheets and maintains stable dispersion at the single-layer level by introducing a cationic polymer to impart strong electrical repulsion to the graphene sheets.

[0040] More specifically, the present invention can provide a graphene ink composition that maintains excellent stability even at high concentrations of 5 to 10 g / L or more and has stable dispersion power over a wide pH range.

[0041] In addition, the present invention can provide a graphene ink composition that maintains stability in a monolayer form without aggregation of the dispersion even in environments with high electrolyte concentrations, enabling its use in various solvent environments and conditions, fundamentally solving the stacking problem between graphene sheets of conventional technology, and preventing degradation of electrical performance.

[0042] Furthermore, the present invention can provide a method for manufacturing a graphene ink composition that simplifies the conventional complex and inefficient manufacturing process, enables eco-friendly mass production without high-temperature treatment, and provides reduced manufacturing costs and environmental sustainability.

[0043] Accordingly, the present invention can contribute to expanding commercial applicability and improving efficiency and scope of application in various electronic and printing technology fields through high-performance, high-concentration water-based graphene ink.

[0044] The effects according to the present invention are not limited to those exemplified above, and various other effects are included in this specification. Brief explanation of the drawing

[0045] FIGS. 1a to 1e illustrate exemplary methods for manufacturing a graphene ink composition according to various embodiments of the present invention. FIG. 2 illustrates an exemplary method for manufacturing a conductive film based on a graphene ink composition according to various embodiments of the present invention. FIGS. 3a to 3c illustrate the configuration of a graphene ink composition-based conductive film according to various embodiments of the present invention. FIGS. 4a to 4b, FIGS. 5a to 5d, and FIG. 6 illustrate the evaluation results of a graphene ink composition and a conductive film using the same according to various embodiments of the present invention. Specific details for implementing the invention

[0046] The advantages of the invention and the methods for achieving them will become clear by referring to the embodiments described below in detail together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below but may be implemented in various different forms. These embodiments are provided merely to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the scope of the invention, and the present invention is defined only by the scope of the claims.

[0047] The shapes, sizes, ratios, angles, numbers, etc. disclosed in the drawings for explaining embodiments of the present invention are exemplary, and therefore the present invention is not limited to the depicted details. Furthermore, in describing the present invention, if it is determined that a detailed description of related known technology may unnecessarily obscure the essence of the present invention, such detailed description is omitted. Where terms such as "comprising," "having," or "consisting of" are used in this specification, other parts may be added unless "only" is used. Where a component is expressed in the singular, it includes cases where it includes the plural unless specifically stated otherwise.

[0048] In interpreting the components, they are interpreted to include a margin of error even in the absence of a separate explicit description.

[0049] The features of each of the various embodiments of the present invention may be combined or combined with one another, either partially or wholly, and as will be fully understood by those skilled in the art, various technical interlocking and operation are possible, and each embodiment may be implemented independently of one another or together in an interlocking relationship.

[0051] For clarity in the interpretation of this specification, the terms used in this specification are defined below.

[0052] The term "graphene ink composition" used in the original specification refers to a material in the form of ink that contains a single layer of reduced graphene oxide (RGO) and has the property of being stably dispersed at a specific concentration.

[0053] Here, "stably dispersed" or "stably dispersed power" can be interpreted as having excellent dispersion power capable of being dispersed in water at a concentration of 5 g / L to 10 g / L or higher, and in particular, having excellent dispersion power while maintaining a monolayer in various solvent environments such as ethanol, methanol, or DMSO, and in various pH ranges from strong acidic conditions of pH 1.0 to strong basic conditions of pH 14.0. Furthermore, it can be interpreted as being able to stably disperse graphene oxide in a reduced state at high concentrations (e.g., 10 g / L or higher) in water-based solutions, but is not limited thereto.

[0054] The term "single-layer graphene" as used in this specification refers to a single-layer graphene sheet formed by the reduction of graphene oxide, and the graphene ink composition according to various embodiments of the present invention can maintain a single layer of reduced graphene oxide without aggregation in water or a solvent, thereby having uniform dispersion power.

[0055] In various embodiments of the present invention, the reduced graphene oxide may be a material in which graphene oxide is reduced by a reducing agent. However, it is not limited thereto.

[0056] As used in this specification, the term "reducing agent" may refer to a chemical or biological substance used to reduce graphene oxide to produce reduced graphene oxide.

[0057] In various embodiments of the present invention, the reducing agent may be at least one of hydrazine monohydrate, sodium borohydride, and hydroquinone, but is not limited thereto.

[0058] The term "cationic polymer" as used in this specification may mean a polymer having the property of carrying a positive charge.

[0059] In various embodiments of the present invention, the cationic polymer can form a stable dispersion through interaction with graphene oxide. For example, the cationic polymer may be polyethyleneimine (PEI) or diallyl dimethylammonium chloride (PDDA), but is not limited thereto.

[0060] For example, the cationic polymer may be at least one of polycarbonyldiimidazolium, chitosan, poly(allylamine hydrochloride) (PAH), ethylenediamine-based polymers, polyquaternium, and polyvinylpyridinium.

[0061] In various embodiments of the present invention, in the process of obtaining reduced graphene oxide, a graphene oxide dispersion may be mixed and stirred in a polymer solution.

[0062] For example, by adding a graphene oxide dispersion to a polymer solution under stirring at 45°C, the electrostatic interaction between the polymer and the graphene oxide can be uniformly achieved. This prevents aggregation and enables the securing of stable graphene oxide within the dispersion.

[0063] As used in this specification, the term "conductive film" may mean an electrically conductive film formed by applying a graphene ink composition on a substrate (or film).

[0064] In various embodiments of the present invention, the conductive film may have a sheet resistance of 1000 Ω / sq to 10,000 Ω / sq and a conductivity of 100 S / m to 1000 S / m, so that it may have excellent durability and conductivity.

[0065] In more diverse embodiments of the present invention, a conductive film is formed by applying a graphene ink composition onto a substrate and annealing it, and provides a uniform conductive path so that electrical performance can be stably maintained.

[0066] Conductive films according to various embodiments of the present invention can exhibit electrical properties without a low annealing temperature (e.g., 100°C or lower), annealing treatment, or additional solvent treatment, thereby enabling an energy-efficient manufacturing process and excellent compatibility with heat-sensitive substrates.

[0067] The conductive film of the present invention having these physical properties can be applied in fields such as flexible electronic devices, displays, sensors, and solar panels.

[0068] The term "annealing" as used in this specification may refer to a process of heating a substrate coated with a graphene ink composition to remove volatile substances and enhance contact between graphene layers to exhibit electrical conductivity.

[0069] In more diverse embodiments, annealing may be performed at a temperature of 100°C or lower. However, it is not limited thereto, and annealing may be performed under a wider variety of conditions as long as conductivity is exhibited.

[0071] Hereinafter, with reference to FIGS. 1a to 1e, a method for manufacturing a graphene ink composition according to various embodiments of the present invention will be described in detail.

[0072] FIGS. 1a to 1e illustrate exemplary methods for manufacturing a graphene ink composition according to various embodiments of the present invention.

[0073] First, referring to FIG. 1a, graphene oxide is dispersed (S110) to obtain dispersed graphene oxide, a polymer solution is prepared (S120), graphene oxide dispersed in the polymer solution is added to obtain a dispersion (S130), a reducing agent is added to the dispersion to obtain reduced graphene oxide (RGO) (S140), and the reduced graphene oxide is redispersed in water to obtain a water-based graphene ink composition (S150).

[0074] In various embodiments of the present invention, in the step (S110) where graphene oxide is dispersed, the graphene oxide may be dispersed in deionized water.

[0075] For example, in the step (S110) where graphene oxide is dispersed, graphene oxide is added to deionized water and can be treated in an ultrasonic bath for about 10 hours. Through the above treatment, a stable and uniform aqueous dispersion can be formed.

[0076] Optionally, the formed graphene oxide dispersion may be sensitive to oxygen and light, so it can be stored in a refrigerated state under dark conditions.

[0077] Referring to FIG. 1b, in a more diverse embodiment of the present invention, graphene oxide dispersed in a polymer solution may be mixed (S1302).

[0078] For example, by adding graphene oxide dispersed in a polymer solution at 45°C, the electrostatic interaction between the polymer and the graphene oxide can be uniformly achieved.

[0079] Meanwhile, referring together with FIG. 1c, in various embodiments of the present invention, a cationic polymer such as polyethyleneimine (PEI) or diallyl dimethylammonium chloride (PDDA) is prepared (S1202) and can be prepared by diluting in deionized water (S1204).

[0080] Accordingly, in the mixing step (S1302), graphene oxide may be mixed in an environment where the cationic polymer solution diluted in deionized water is stirred, but is not limited thereto.

[0081] By this mixing step (S1302), the stability of the dispersion is further improved, and it may be possible to manufacture a uniform water-based graphene ink composition.

[0082] Meanwhile, referring to FIG. 1d, in a more diverse embodiment of the present invention, a reducing agent is added to a dispersion to obtain a mixture in order to obtain reduced graphene oxide (S1402), the mixture is placed in an oil bath (S1404), and heat treatment is performed to obtain reduced graphene oxide (S1406).

[0083] For example, in the step (S1402) where a reducing agent is added to the dispersion, at least one reducing agent selected from hydrazine monohydrate, sodium borohydride, and hydroquinone at a concentration of 98% may be added to prepare a mixture. Then, in the step (S1404) where it is placed in an oil bath and the step (S1406) where heat treatment is performed, the mixture may be placed in an oil bath set to 100°C and the reduction reaction may proceed through heat treatment for about 12 hours.

[0084] Through this process, the oxygen content of the graphene oxide is reduced and electron-electron coupling is restored, and as a result, electrical conductivity can be imparted to the reduced graphene oxide.

[0085] Referring further to FIG. 1e, in various embodiments of the present invention, after the step (S140) of adding a reducing agent, the reduced graphene oxide (RGO) is centrifuged (S160) so that the residual reducing agent or residual polymer solution is removed from the reduced graphene oxide, and the reduced graphene oxide from which the residual reducing agent or residual polymer solution has been removed is redispersed in water (S1502).

[0086] For example, in the step (S160) where the reduced graphene oxide is centrifuged, the mixture in which the reduction reaction is completed may be fed into a high-speed centrifuge and centrifuged at a speed of about 20,000 rpm for 30 minutes. Through this, excess reducing agent and excess cationic polymer may be removed.

[0087] The step (S160) of centrifuging the reduced graphene oxide can be repeated multiple times, and after each step, the recovered precipitate is washed with deionized water and additional removal of residual impurities can be performed.

[0088] Next, in the step of redispersing in water (S1502), the reduced graphene oxide from which the residual reducing agent and polymer have been removed is redispersed in deionized water to finally obtain a stable water-based graphene ink composition.

[0089] In more diverse embodiments, the step of redispersing in water (S1502) may be performed using ultrasonic treatment or mechanical stirring, but is not limited thereto.

[0090] According to the method for preparing a water-based graphene ink composition according to the various embodiments above, it may be possible to obtain a stable single-layer reduced graphene oxide-based graphene ink composition.

[0091] More specifically, a graphene ink composition according to various embodiments of the present invention comprises a single layer of reduced graphene oxide and can be stably dispersed in water at a concentration of 5 g / L to 10 g / L or higher.

[0092] In addition, the graphene ink composition can maintain dispersion power over a wide pH range from strongly acidic to strongly basic, and can have stable dispersion characteristics in various solvent environments.

[0093] In particular, graphene ink compositions according to various embodiments of the present invention can have long-term stability through electrostatic interactions with cationic polymers. For example, reduced graphene oxide can maintain a uniform dispersion state without ultrasonic treatment or mechanical stirring, while maintaining a monolayer without aggregation.

[0094] Furthermore, the graphene ink composition according to various embodiments of the present invention has the characteristic of being able to exhibit conductivity at a low annealing temperature or without an annealing step, and can be applied to various manufacturing processes such as inkjet printing and spray coating for forming conductive films or patterns.

[0095] Through this, the graphene ink composition according to various embodiments of the present invention can be applied in various application fields requiring high-performance conductive materials, such as flexible electronic devices, sensors, displays, and solar panels.

[0096] Accordingly, the present invention can overcome the limitations of existing high-concentration graphene inks, such as instability, high annealing temperature, and limited application possibilities.

[0098] Hereinafter, a method for manufacturing a graphene ink-based conductive film according to various embodiments of the present invention will be described with reference to FIG. 2.

[0099] Referring to FIG. 2, a water-based graphene ink composition is applied to a substrate (S210), and the applied substrate is heated (S220) so that the water-based graphene ink composition solidifies on the substrate.

[0100] More specifically, in the step (S210) where the graphene ink composition is applied, a patterned photoresist may be coated on an insulating substrate, or a pattern mask may be provided on the substrate. A water-based graphene ink composition according to various embodiments of the present invention may be selectively sprayed onto a specific area of ​​the substrate through inkjet printing, spray coating, or other application methods.

[0101] At this time, graphene ink can be applied to areas not covered by photoresist or a mask.

[0102] Next, in the solidification step (S220), the substrate coated with the water-based graphene ink composition can be heated to 80°C to 100°C. Through this, volatile components in the graphene ink composition evaporate, and the contact between the reduced graphene oxide sheets is strengthened, thereby forming a solidified film that has conductivity.

[0103] However, it is not limited to this, and the conductive film itself, on which graphene ink is disposed on the substrate obtained in the step (S210) where the graphene ink composition is applied, may also have conductivity.

[0104] In other words, the annealing step may be performed optionally, but is not limited to this.

[0105] A graphene ink-based conductive film manufactured according to the method for manufacturing a conductive film according to various embodiments of the present invention above can have a sheet resistance of 1000 Ω / sq to 10,000 Ω / sq and exhibit a conductivity of 100 S / m to 1000 S / m.

[0106] In particular, the conductive film according to various embodiments of the present invention can stably exhibit electrical conductivity without a low annealing temperature, annealing treatment, or additional solvent treatment, thereby enabling an efficient manufacturing process and allowing electrodes to be stably formed even on heat-sensitive substrates such as plastic or paper.

[0107] Furthermore, due to the uniform dispersion characteristics of the graphene ink composition, the conductive film according to various embodiments of the present invention possesses excellent structural stability and can provide high durability in mechanical stress environments. This stability ensures that the film maintains its electrical performance even when used for a long time or exposed to repeated environmental changes.

[0108] Accordingly, conductive films according to various embodiments of the present invention can be utilized in high-performance applications such as flexible electronic devices, sensors, displays, and solar panels.

[0110] Hereinafter, the configuration of a conductive film according to various embodiments of the present invention will be described with reference to FIGS. 3a to 3c.

[0111] First, referring to (a) and (b) of FIG. 3a, a conductive film (300) according to various embodiments of the present invention may be composed of a water-based graphene ink layer (310) and a substrate (320).

[0112] At this time, the water-based graphene ink layer (310) can be formed on the substrate (320) through inkjet printing, spray coating, or other coating techniques. This water-based graphene ink layer (310) may be provided in the form of a film having uniform conductivity, comprising a single layer of reduced graphene oxide.

[0113] At this time, the conductive film (300) can form a uniform conductive network by forming a water-based graphene ink layer (310) as a single film structure on a substrate (320).

[0114] In more diverse embodiments of the present invention, the substrate (320) may be composed of polyurethane (PU), polyethylene terephthalate (PET), or polyimide (PI) having flexible properties, but is not limited thereto, and may be replaced with glass, ceramic, or other insulating materials. Such substrates may be selected in a more diverse manner depending on the purpose of the conductive film.

[0115] Referring further to FIGS. 3b and 3c, in more diverse embodiments of the present invention, the water-based graphene ink layer (310) may be formed as a single electrode pattern (see FIG. 3b) or a multi-electrode pattern (see FIG. 3c).

[0116] More specifically, water-based graphene ink layers (310-1, 310-2, 310-3) can be formed in a patterned form, which can be realized through a pattern mask or photoresist technique. These patterns can selectively provide conductivity in various forms, such as sensors or electronic circuits.

[0117] At this time, the thickness and pattern size of the water-based graphene ink layer (310) can be adjusted according to the coating process and the concentration of the graphene ink.

[0118] For example, the thickness of the water-based graphene ink layer (310-1, 310-2, 310-3) can be set to a range of 100 nm to 1 μm, thereby allowing the conductive film to exhibit electrical and mechanical properties tailored to specific application purposes. However, it is not limited to this.

[0119] Accordingly, the conductive film (300, 300', 300'') according to various embodiments of the present invention provides uniform conductivity and can be applied to various application fields.

[0121] Evaluation: Evaluation of graphene ink compositions according to various embodiments of the present invention

[0122] Hereinafter, with reference to FIGS. 4a to 4b, FIGS. 5a to 5d, and FIG. 6, the evaluation results of graphene ink compositions according to various embodiments of the present invention will be described.

[0123] First, referring to FIG. 4a, a Raman spectrum is shown after drying a reduced graphene oxide-based ink composition according to various embodiments of the present invention. At this time, the Raman spectrum can provide information about the structural characteristics and defects of the reduced graphene oxide and the restoration state of the graphene layer.

[0124] More specifically, major peaks of the D band, G band, and 2D band appear in the Raman spectrum of the reduced graphene oxide-based graphene ink composition, which may mean that the graphene ink composition can restore the sp² network of graphene, maintain a stable structure, and exhibit conductive properties.

[0125] Referring further to FIG. 4b, the UV-Vis spectra of commercially available graphene oxide (GO-VG50) and reduced graphene oxide ink (RGO ink) provided as an ink composition according to various embodiments of the present invention are shown.

[0126] In this case, the UV-Vis spectrum can provide important information for analyzing the reduction state and electronic structure changes of graphene oxide.

[0127] More specifically, the spectrum of graphene oxide (GO-V50) has an absorption peak at approximately 235 nm, and this absorption peak may indicate an oxidized structure in which the sp² network is damaged due to oxygen functional groups.

[0128] Meanwhile, the spectrum of reduced graphene oxide ink (RGO ink) shows an absorption peak shifted to about 265 nm, which may indicate that the sp² carbon network was restored through the reduction process.

[0129] These results may imply that the electrical and optical performance of the reduced graphene oxide ink is improved compared to graphene oxide. That is, the reduced graphene oxide ink obtained according to various embodiments of the present invention may have superior electronic and optical properties compared to conventional graphene oxide.

[0131] Next, referring to FIG. 5a, an image related to the dispersion stability of reduced graphene oxide (RGO) in water according to various embodiments of the present invention is shown.

[0132] More specifically, a reduced graphene oxide dispersion at a concentration of 0.5 g / L at neutral pH is compared and illustrated when it does not contain a cationic polymer (Fig. 5a (b)), when it contains polyethyleneimine (Fig. 5a (a)), and when it contains polydiallyldimethylammonium chloride (Fig. 5a (c)).

[0133] First, when reduced graphene oxide is dispersed in water without the addition of cationic polymers, it is observed that the reduced graphene oxide aggregates and settles or is dispersed unevenly within the dispersion. This may indicate that in the absence of cationic polymers, electrostatic interactions or aggregation between the reduced graphene oxide particles are not effectively prevented, resulting in reduced dispersion stability.

[0134] Next, when polyethylene is added as a cationic polymer, the reduced graphene oxide is shown to be uniformly and stably dispersed. Furthermore, when polydiallyldimethylammonium chloride is added as a cationic polymer, the reduced graphene oxide is shown to be uniformly and stably dispersed, similar to the results above.

[0135] In other words, these results may imply that the cationic polymer forms a stable dispersion through electrostatic interactions with reduced graphene oxide, contributing to the maintenance of the transparency and uniformity of the dispersion.

[0136] Furthermore, referring to FIG. 5b, the dispersion state of reduced graphene oxide according to various embodiments of the present invention is shown when NaCl is not added (Fig. 5b (a)) and when NaCl is added (Fig. 5b (b)).

[0137] More specifically, when reduced graphene oxide is dispersed in water without the addition of NaCl, it is shown that the reduced graphene oxide is uniformly dispersed. Furthermore, when reduced graphene oxide is dispersed in an environment with high electrolyte concentration by adding NaCl, it is shown that the reduced graphene oxide remains uniformly and stably dispersed.

[0138] These results may imply that the water-based graphene ink composition of the present invention can prevent aggregation between reduced graphene oxides and maintain dispersion stability even under conditions of high electrolyte concentration.

[0139] Referring to FIG. 5c, a dispersion of reduced graphene oxide in a strongly acidic environment (Fig. 5c (a)) and a dispersion of reduced graphene oxide in a strongly basic environment (Fig. 5c (b)) according to various embodiments of the present invention are shown.

[0140] More specifically, it is shown that the graphene oxide dispersion is uniformly dispersed under strongly acidic conditions such as pH 1. This may mean that the water-based graphene ink composition of the present invention can suppress aggregation between graphene oxide dispersions even in a strongly acidic environment and maintain a stable dispersion state.

[0141] Furthermore, it is shown that the graphene oxide dispersion has a uniformly and stably dispersed state under strong basic conditions such as pH 14. This may mean that the water-based graphene ink composition of the present invention can maintain stability even in a basic environment.

[0142] In other words, the above results mean that the water-based graphene ink composition of the present invention can maintain stable dispersion characteristics over a wide pH range from strongly acidic (pH 1) to strongly basic (pH 14).

[0143] Based on these characteristics, the graphene ink composition according to various embodiments of the present invention can be applied under various environmental conditions and can be utilized in fields such as electronic devices, sensors, and coatings.

[0144] Referring to FIG. 5d, a film having a graphene ink composition according to various embodiments of the present invention on a paper filter is shown. In particular, it is shown that the graphene ink composition is evenly dispersed on the paper filter and forms a homogeneous film.

[0145] This implies that the water-based graphene ink composition according to various embodiments of the present invention can be uniformly applied to various substrates and may be applicable as a conductive film, sensor, electronic device, or coating material.

[0147] Next, referring to FIG. 6, the main characteristics of a graphene ink composition according to various embodiments of the present invention are illustrated.

[0148] More specifically, in the evaluation of dispersibility in water, the graphene ink composition of the present invention can be stably dispersed in water at a concentration of up to 5 g / L to 10 g / L or more. This high dispersibility may mean that the graphene ink composition of the present invention can be maintained uniformly without aggregation even at high concentrations.

[0149] Furthermore, in the evaluation of the pH tolerance of water-based ink, the graphene ink composition of the present invention can maintain stability over a wide pH range from strongly acidic (pH 1) to strongly basic (pH 14). This may mean that the graphene ink composition can maintain dispersion properties even in various chemical environments.

[0150] Next, in the evaluation of dispersibility in different solvents, the graphene ink composition of the present invention can be stably dispersed at a concentration of up to 5 g / L to 10 g / L in various solvents such as ethanol, methanol, isopropanol, dimethyl sulfoxide (DMSO), n-methylpyrrolidone (NMP), and dimethylformamide (DMF). This implies that the ink composition of the present invention can maintain higher stability even under organic solvent conditions, and in particular, can maintain stable dispersion power when an organic solvent is used in the process.

[0151] Next, in the evaluation of the sheet resistance of the prepared film, the conductive film based on the graphene ink composition of the present invention is shown to have a sheet resistance of 1,000 Ω / sq to 10,000 Ω / sq.

[0152] Furthermore, in the evaluation of the conductivity of the prepared film, the conductive film based on the graphene ink composition of the present invention is shown to have a conductivity of 100 S / m to 1000 S / m. Such high conductivity may mean that the ink composition of the present invention can provide suitable properties for applications such as conductive films, electronic devices, and sensors.

[0153] According to the evaluation results above, the water-based graphene ink composition of the present invention maintains stable dispersion power without aggregation at high concentrations and can exhibit excellent dispersion characteristics even under various organic solvent conditions and a wide pH range from strongly acidic to strongly basic.

[0154] These characteristics demonstrate that the ink composition of the present invention can stably maintain a single layer of reduced graphene oxide to form a uniform conductive film.

[0155] In particular, the conductive film based on the graphene ink composition of the present invention exhibits a sheet resistance of 1000 Ω / sq to 10,000 Ω / sq and a conductivity of 100 S / m to 1000 S / m, which means that it can be utilized as a high-performance material in applications such as electronic devices, sensors, and conductive coatings.

[0156] Furthermore, the method for manufacturing a graphene ink composition according to various embodiments of the present invention provides an annealing treatment at a low temperature, and may also provide the advantages of energy-efficient manufacturing and usability even on heat-sensitive substrates.

[0157] That is, the present invention can provide a highly versatile conductive material by providing a graphene ink composition that maintains the stability of a single layer by reducing a graphene oxide dispersion.

[0158] Although embodiments of the present invention have been described in more detail with reference to the attached drawings, the present invention is not necessarily limited to these embodiments and may be modified in various ways within the scope of the technical spirit of the present invention. Accordingly, the embodiments disclosed in the present invention are intended to explain, not limit, the technical spirit of the present invention, and the scope of the technical spirit of the present invention is not limited by these embodiments. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive. The scope of protection of the present invention shall be interpreted by the claims below, and all technical spirits within an equivalent scope shall be interpreted as being included within the scope of rights of the present invention. Explanation of the symbols

[0159] 300, 300', 300'': Conductive film 310, 310-1, 310-2, 310-3: Graphene ink layer 320: Board

Claims

Claim 1 A water-based graphene ink composition comprising a single layer of reduced graphene oxide (RGO), wherein the graphene ink composition has dispersibility that disperses in water at a concentration of 5 g / L to 10 g / L. Claim 2 In claim 1, the water-based graphene ink composition is a graphene ink composition that maintains the dispersion power at pH 1 to pH 14. Claim 3 In claim 1, the water-based graphene ink composition is a graphene ink composition that maintains the dispersion force in a solvent environment. Claim 4 A substrate; a conductive film comprising a graphene ink composition of any one of claims 1 to 3 on the substrate. Claim 5 In claim 4, the conductive film is a conductive film having a sheet resistance of 1,000 Ω / sq to 10,000 Ω / sq. Claim 6 In claim 4, the conductive film is a conductive film having a conductivity of 100 S / m to 1000 S / m. Claim 7 In claim 4, the conductive film is a conductive film having an annealing temperature of 100°C or less for the expression of conductivity. Claim 8 A method for preparing a water-based graphene ink composition, comprising the steps of: dispersing graphene oxide to obtain dispersed graphene oxide; preparing a polymer solution; adding the dispersed graphene oxide onto the polymer solution to obtain a dispersion; adding a reducing agent to the dispersion to obtain reduced graphene oxide (RGO); and redispersing the reduced graphene oxide in water to obtain a water-based graphene ink composition. Claim 9 A method for preparing a water-based graphene ink composition, wherein the step of adding the dispersed graphene oxide in claim 8 comprises the step of mixing the dispersed graphene oxide into the polymer solution. Claim 10 A method for preparing a water-based graphene ink composition, wherein the step of preparing the polymer solution comprises the step of preparing a cationic polymer and the step of diluting the cationic polymer in water. Claim 11 A method for preparing a water-based graphene ink composition, wherein the cationic polymer in claim 10 is polyethyleneimine (PEI) or diallyl dimethylammonium chloride (PDDA). Claim 12 A method for preparing a water-based graphene ink composition, wherein the step of adding the reducing agent comprises: adding the reducing agent to the dispersion to obtain a mixture; placing the mixture in an oil bath; and performing a heat treatment to obtain the reduced graphene oxide. Claim 13 A method for preparing a water-based graphene ink composition according to claim 8, wherein the reducing agent is at least one of hydrazine monohydrate, sodium borohydride, and hydroquinone. Claim 14 A method for preparing a water-based graphene ink composition, wherein, after the step of adding the reducing agent in claim 8, the method further comprises the step of centrifuging the reduced graphene oxide (RGO) so as to remove any residual reducing agent or residual polymer solution from the reduced graphene oxide, and the redispersing step comprises the step of redispersing the reduced graphene oxide from which the residual reducing agent or residual polymer solution has been removed in water. Claim 15 A method for preparing a water-based graphene ink composition according to claim 9, wherein the water-based graphene ink composition has dispersibility that disperses in water at a concentration of 5 g / L to 10 g / L.

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