JP7567422B2 - Resin composition and cured film using same - Google Patents

Description

The present invention relates to a resin composition containing graphene and a heat-resistant resin, and a cured film thereof.

In recent years, conductive resin compositions such as conductive paints and conductive adhesives have been widely used in applications such as solar cells, high-temperature semiconductor circuits, electromagnetic shielding for automotive parts, and solder replacements. The important properties of conductive resin compositions used in such applications are electrical conductivity, heat resistance, and adhesion to substrates, and improvements in these properties are required. In particular, applications such as high-temperature semiconductor circuits and solder replacements may involve use at temperatures of around 300°C, making further improvements in heat resistance necessary.

As the conductive resin composition, there have been disclosed, for example, a conductive paste comprising a conductive powder, a binder resin, and an organic solvent, the binder resin being characterized in that it contains polyamideimide and/or polyimide copolymerized with at least one component selected from the group consisting of butadiene-based rubber, isoprene-based rubber, butyl rubber, ethylene-propylene rubber, chloroprene rubber, fluororubber, silicone rubber, urethane rubber, polyester, polycarbonate, polyether, polylactone, and dimer acid (see, for example, Patent Document 1); a conductive paste comprising a resin component containing polyvinyl acetal (A) and a curable resin (B), and a fiber having an aspect ratio of 10 to 15,000 and an average fiber diameter d and a carbon component containing carbon nanotubes (C) having _{a C} of 5 to 100 nm, wherein the content of the resin (A) in the resin component is 10 to 70 mass % and the content of the carbon nanotubes (C) is 2 to 70 mass parts relative to 100 mass parts of the resin component (see, for example, Patent Document 2); and a carbon material composite composition containing a carbon material, wherein the carbon material has a graphene skeleton and the composition further contains a polyimide and/or a precursor thereof (see, for example, Patent Document 3).

JP 2004-221006 A JP 2014-28900 A JP 2016-127210 A

The conductive paste described in Patent Document 1 improves the conductivity and adhesion, but the dispersibility and heat resistance of the conductive powder are still insufficient, and there is a problem that in a high-temperature environment of about 300°C, the conductivity of the cured film obtained from the resin composition and the adhesion to the substrate are reduced due to thermal decomposition and cracking of the resin. On the other hand, the conductive resin composition disclosed in Patent Document 2 improves the dispersibility of the carbon component, but the heat resistance is still insufficient, and there is a problem that in a high-temperature environment of about 300°C, the adhesion to the substrate and the conductivity are reduced. In addition, the carbon material composite composition disclosed in Patent Document 3 improves the thermoelectric performance, but the dispersibility of the carbon component is insufficient, and there is a problem that the conductivity and adhesion to the substrate are reduced in a high-temperature environment.

The present invention aims to provide a resin composition that can improve the dispersibility of graphene in a heat-resistant resin and produce a cured film that has excellent heat resistance, electrical conductivity in high-temperature environments, and adhesion to the substrate.

In order to solve the above problems, the present invention provides a resin composition that includes graphene having an elemental ratio of nitrogen to carbon (N/C ratio) of 0.005 or more and 0.030 or less as measured by X-ray photoelectron spectroscopy, and a heat-resistant resin having nitrogen atoms.

The resin composition of the present invention has excellent dispersibility of graphene. The resin composition of the present invention can provide a cured film that has excellent heat resistance, electrical conductivity in high-temperature environments, and adhesion to the substrate.

<Resin Composition>
The resin composition of the present invention contains graphene having an elemental ratio of nitrogen to carbon (N/C ratio) of 0.005 or more and 0.030 or less as measured by X-ray photoelectron spectroscopy, and a heat-resistant resin having nitrogen atoms. By combining graphene having an N/C ratio in this range with a heat-resistant resin having nitrogen atoms, the dispersibility of graphene in the resin composition can be improved and sufficient conductivity can be exhibited with a small amount of graphene, so that the heat resistance, conductivity in a high-temperature environment, and adhesion to a substrate of a cured film obtained from the resin composition can be improved.

<Graphene>
Graphene is thin, planar, and has many conductive paths per unit mass, and acts as the core of a strong conductive network in a resin composition. In a narrow sense, graphene refers to a sheet of ^sp2- bonded carbon atoms with a thickness of one atom (single-layer graphene), but in this specification, the term graphene also refers to a flaky form in which single-layer graphene is stacked. Furthermore, graphene may be surface-treated for the purpose of improving dispersibility, and in this specification, graphene to which such a surface treatment agent is attached is also referred to as "graphene".

The size of the graphene in the plane direction is preferably 0.1 μm or more, more preferably 0.5 μm or more, and even more preferably 1 μm or more, from the viewpoint of facilitating the formation of an electronic conduction network in the resin composition and further improving the electrical conductivity. On the other hand, the size of the graphene in the plane direction is preferably 10 μm or less, more preferably 5 μm or less, and even more preferably 3 μm or less, from the viewpoint of further improving the dispersibility in the resin composition and the adhesion to the substrate in a high-temperature environment. The size of the graphene in the plane direction here refers to the average value of the longest diameter and the shortest diameter of the graphene plane. The size of the graphene in the plane direction can be determined by applying a dilute graphene dispersion onto a substrate, enlarging and observing the graphene using an electron microscope at a magnification at which the graphene fits within an appropriate field of view, measuring the longest diameter and the shortest diameter for 10 randomly selected graphenes, calculating the size of each graphene in the plane direction from the average value, and calculating the arithmetic average value. Examples of methods for extracting graphene from a resin composition or a cured film include crushing the resin composition or the cured film using a freeze crusher or the like, and then drying the graphene extracted using N-methyl-2-pyrrolidone (NMP). In addition, since the size of the graphene in the planar direction does not change in the resin composition or the cured film in a typical manufacturing method, if the graphene used as the raw material for the resin composition is known, it may be measured directly from the raw graphene.

The size of the graphene in the planar direction can be adjusted to a desired range, for example, by using a preferred manufacturing method in the graphene manufacturing method described below, selecting the time of the micronization process, etc. The size in the planar direction can be reduced by extending the time of the micronization process, and the size in the planar direction can be kept large by shortening the time of the micronization process or by not performing the micronization process at all.

The crystallite size of graphene calculated by Scherrer's formula from the peak corresponding to the (002) plane of the graphene crystal in the X-ray diffraction method is preferably 2 nm or less. In this way, the crystallite size in the direction perpendicular to the basal plane of graphene is small, i.e., the thickness is thin, so that an efficient electron conduction path is formed by graphene in the resin composition, and the conductivity can be further improved even when the graphene content is small. Here, the X-ray diffraction measurement of graphene is performed on graphene that has been vacuum dried at a temperature of 60° C. for 12 hours under the conditions of a scanning range of 5° to 50°, a step size of 0.016°, and a scanning speed of 1 step/second, and the crystallite size can be calculated from the half-width of the peak (near 2θ/θ=25°) corresponding to the (002) plane of the graphene crystal by Scherrer's formula. In addition, as a method for extracting graphene from a resin composition or a cured film, for example, a method of crushing the resin composition or the cured film using a freeze crusher or the like, and then drying the graphene extracted using N-methylpyrrolidone (NMP) can be mentioned. In addition, since the graphene crystallite size does not change in the resin composition or in the cured film in a typical manufacturing method, if the graphene used as the raw material for the resin composition is known, it may be measured directly from the raw graphene that has been vacuum-dried.

The size of the graphene crystallite diameter can be adjusted to a desired range, for example, by using a preferred manufacturing method or a surface treatment agent in the graphene manufacturing method described below, or by adjusting the amount of the surface treatment agent added to a preferred range. For example, by adding an appropriate amount of a preferred surface treatment agent and stirring, the graphene can be peeled off and the crystallite diameter can be reduced. In addition, in the graphene manufacturing process described below, the crystallite diameter can be reduced by increasing the shear rate in the strong stirring step or by extending the stirring time.

In the present invention, the element ratio of nitrogen to carbon (N/C ratio) of graphene measured by X-ray photoelectron spectroscopy is 0.005 or more and 0.030 or less. When graphene contains nitrogen, the dispersibility of graphene in the resin composition is increased by the interaction between the nitrogen atoms in the heat-resistant resin and the nitrogen atoms on the graphene, and a small amount of graphene can improve the conductivity of the cured film, especially the conductivity under a high temperature environment. If the N/C ratio is less than 0.005, the dispersibility of graphene in the resin composition decreases, so that the conductivity of the cured film, especially the conductivity under a high temperature environment, decreases. In addition, since the dispersibility of graphene decreases, the cured film becomes more likely to peel off from the substrate starting from the graphene aggregation portion, and the adhesion of the cured film, especially under a high temperature environment, also decreases. The N/C ratio is preferably 0.006 or more, more preferably 0.008 or more. On the other hand, if the N/C ratio exceeds 0.030, the conductivity of the graphene itself decreases. In addition, since the adhesiveness at the interface between the graphene and the heat-resistant resin is reduced, peeling is likely to occur starting from the interface, and the adhesion of the cured film is also reduced, particularly in a high-temperature environment. The N/C ratio is preferably 0.020 or less, more preferably 0.018 or less, and even more preferably 0.016 or less. Here, the N/C ratio can be measured by obtaining a photoelectron spectrum of graphene using an X-ray photoelectron spectrometer, such as PHI Quantera II (manufactured by Ulvac-PHI Co., Ltd.), Quantera SXM (manufactured by Ulvac-PHI Co., Ltd.), or JPS-9030 (manufactured by JEOL Ltd.), and quantifying the element ratio from the peak area ratio. In X-ray photoelectron spectroscopy, soft X-rays are irradiated onto the surface of a sample placed in an ultra-high vacuum, and photoelectrons emitted from the surface are detected by an analyzer. These photoelectrons are measured by wide scanning to determine the binding energy value of the bound electrons in the material, thereby obtaining elemental information on the surface of the material. Furthermore, the element ratio can be quantified using the peak area ratio. As a method for extracting graphene from a resin composition or a cured film, for example, a method of crushing the resin composition or the cured film using a freeze crusher or the like, and then drying the graphene extracted using N-methylpyrrolidone (NMP) can be mentioned. When graphene is extracted from a resin composition or a cured film, it is preferable to perform the measurement using an X-ray photoelectron spectrometer that can measure with a beam diameter of 10 μm, such as PHI Quantera II (manufactured by Ulvac-PHI Co., Ltd.), in order to selectively measure the region of only graphene. In addition, since the N/C ratio of graphene does not change in a resin composition or a cured film in a general production method, when the graphene that is the raw material of the resin composition is known, it may be measured directly from the raw graphene that has been vacuum-dried.

Methods for introducing nitrogen into graphene include, for example, doping the graphene surface with nitrogen atoms, introducing molecules containing nitrogen atoms by reacting with oxygen functional groups remaining on the graphene, and surface treatment for non-covalently adsorbing molecules containing nitrogen atoms to the graphene. Among these, surface treatment is preferred, as it can further improve the dispersibility of graphene in the resin composition.

As the surface treatment agent, a compound having a phenyl group and/or an amino group is preferable, for example, antipyrine, aminopyrine, 4-aminoantipyrine, 1-phenyl-3-methyl-5-pyrazolone, 4-benzoyl-3-methyl-1-phenyl-2-pyrazolin-5-one, 1-(2-chlorophenyl)-3-methyl-2-pyrazolin-5-one, 5-oxo-1-phenyl-2-pyrazoline-3-carboxylic acid, 1-(2-chloro-5-sulfophenyl)-3-methyl-5-pyrazolone, 1-(4-chlorophenyl)-3-methyl-2-pyrazolin-5-one, 1-(4-sulfophenyl)-3-methyl-5-pyrazolone, 3-chloroaniline, benzylamine, 2-phenylethylamine, 1-naphthylamine, dopamine hydrochloride, dopamine, dopa, etc. Two or more of these may be used. The N/C ratio can be adjusted to the desired range, for example, by changing the type and amount of the surface treatment agent.

In the present invention, the oxygen to carbon element ratio (O/C ratio) of graphene measured by X-ray photoelectron spectroscopy is preferably 0.08 or more and 0.30 or less. From the viewpoint of further improving the dispersibility of graphene, the O/C ratio is more preferably 0.09 or more, and even more preferably 0.12 or more. On the other hand, from the viewpoint of recovering the π-electron conjugated structure of graphene, further improving the conductivity of graphene, and further suppressing the decrease in adhesion to the substrate caused by gas generation derived from functional groups in a high-temperature environment, the O/C ratio is preferably 0.25 or less, more preferably 0.20 or less, and even more preferably 0.18 or less. Here, the O/C ratio can be determined in the same manner as the above-mentioned N/C ratio.

The oxygen atoms on the graphene surface are derived from highly polar functional groups containing oxygen atoms, such as hydroxyl groups (-OH), carboxyl groups (-COOH), ester bonds (-C(=O)-O-), ether bonds (-C-O-C-), carbonyl groups (-C(=O)-), and epoxy groups. Note that while a surface treatment agent is applied to the graphene, oxygen atoms derived from functional groups of such surface treatment agents as well as functional groups of the graphene itself are included in the "oxygen atoms on the graphene surface." In other words, in graphene to which a surface treatment agent is applied, it is preferable that the O/C ratio of the surface after treatment with the surface treatment agent is within the above range.

For example, when a chemical peeling method is used, the O/C ratio can be adjusted by changing the degree of oxidation of the graphene oxide raw material or the amount of the surface treatment agent. The higher the degree of oxidation of the graphene oxide, the greater the amount of oxygen remaining after reduction, and the lower the degree of oxidation of the graphene oxide, the lower the amount of oxygen remaining after reduction. Also, the greater the amount of the surface treatment agent having acidic groups attached, the greater the amount of oxygen can be.

When two or more types of graphene with different properties are included, it is preferable that the graphene as a whole has the above properties.

The content of graphene in the resin composition of the present invention is preferably 1 part by weight or more, more preferably 3 parts by weight or more, and even more preferably 5 parts by weight or more, per 100 parts by weight of the heat-resistant resin having a nitrogen atom described later, from the viewpoint of further improving the electrical conductivity, particularly electrical conductivity under a high-temperature environment. On the other hand, the content of graphene is preferably 30 parts by weight or less, more preferably 20 parts by weight or less, and even more preferably 10 parts by weight or less, per 100 parts by weight of the heat-resistant resin having a nitrogen atom described later, from the viewpoint of further improving the adhesion of the cured film to the substrate, particularly under a high-temperature environment.

The graphene used in the present invention may be produced by a physical exfoliation method or a chemical exfoliation method. When produced by a chemical exfoliation method, the method for producing graphene oxide is not particularly limited, and known methods such as the Hummers method can be used. Commercially available graphene oxide may also be used.

The chemical peeling method preferably includes a step of obtaining graphene oxide by oxidatively peeling graphite (graphite peeling step) and a step of performing reduction (reduction step) in this order. If necessary, a step of attaching a surface treatment agent to graphene (surface treatment step) and/or a step of adjusting the size of the graphene in the planar direction (fine-refining step) may be included between the graphite peeling step and the reduction step. When surface-treated graphene is used, the surface treatment agent may be attached to graphene, or the surface-treated graphene may be obtained by attaching the surface treatment agent to graphene oxide and then performing a reduction treatment. When graphene is fine-refined, the graphene oxide may be fine-refined, or the graphene after reduction may be fine-refined. From the viewpoint of uniformity of the reduction reaction, it is preferable to perform the reduction step in a fine-refined state of graphene oxide, and it is preferable to perform the fine-refining step before or during the reduction step. For this reason, it is preferable to have the graphite peeling step, the surface treatment step, the fine-refining step, and the reduction step in this order.

The graphene used in the present invention is preferably used in the form of a dispersion in order to further improve dispersibility in the resin composition. When producing the dispersion, it is preferable to further include a step of mixing the intermediate dispersion that has undergone the reduction step with an organic solvent (organic solvent mixing step), and a step of stirring the intermediate dispersion containing the organic solvent at a peripheral speed of the rotating blade of the mixer of 6 m/s or more and 70 m/s or less (strong stirring step).

The preferred aspects of each step are described below.

[Graphite peeling process]
First, graphene oxide is obtained by oxidative peeling of graphite. The oxidation degree of graphene oxide can be adjusted by changing the amount of oxidizing agent used in the oxidation reaction of graphite. Specifically, the greater the amount of sodium nitrate and potassium permanganate used in the oxidation reaction relative to graphite, the higher the oxidation degree, and the smaller the amount, the lower the oxidation degree. The weight ratio of sodium nitrate to graphite is preferably 0.200 to 0.800. The ratio of potassium permanganate to graphite is preferably 1.00 to 4.0.

[Surface treatment process]
Next, the graphene oxide and the surface treatment agent are mixed to adhere the surface treatment agent to the graphene. Examples of the mixing method include a method of mixing using a mixer or kneader such as an automatic mortar, a triple roll, a bead mill, a planetary ball mill, a homogenizer, a homodisper, a homomixer, a planetary mixer, or a twin-screw kneader.

[Miniaturization process]
Next, the graphene oxide is refined. Examples of the refinement method include a method of applying ultrasonic waves, a method of colliding a pressurized intermediate dispersion against a single ceramic ball, and a method of using a liquid-liquid shear type wet jet mill in which pressurized intermediate dispersions are collided with each other to perform dispersion. In particular, ultrasonic treatment is preferable because it is a media-less dispersion method. In the refinement step, the graphene oxide or graphene tends to be refined as the output and treatment pressure are higher, and tends to be refined as the treatment time is longer. The size of the graphene after reduction can be adjusted by the type, treatment conditions, and treatment time of the refinement treatment in the refinement step. In order to adjust the size parallel to the graphene layer to the above-mentioned range, the solid content concentration of the graphene oxide or graphene in the refinement step is preferably 0.01% by weight or more and 2% by weight or less. In addition, the ultrasonic output when the ultrasonic treatment is performed is preferably 100 W or more and 3000 W or less.

[Reduction process]
Next, the fine graphene oxide is reduced. A preferable reduction method is chemical reduction. In the case of chemical reduction, examples of the reducing agent include organic reducing agents and inorganic reducing agents. Among these, inorganic reducing agents are preferable because of ease of cleaning after reduction, and sodium dithionite, potassium dithionite, and the like are more preferable.

[Organic solvent mixing step]
In the organic solvent mixing step, the intermediate dispersion liquid and an organic solvent are mixed in order to replace the water in the intermediate dispersion liquid after the reduction step with the organic solvent. In the organic solvent mixing step, the intermediate dispersion liquid obtained through the reduction step is directly mixed with the organic solvent. That is, from the end of the reduction step to the mixing with the organic solvent in the organic solvent mixing step, the intermediate dispersion liquid is always in a dispersion state, and an operation such as freeze-drying for removing the dispersion medium from the intermediate dispersion liquid and recovering graphene in a powder state is not performed.

[Strong stirring process]
In the strong stirring step, a high shear mixer is used to perform stirring at a shear rate of 5,000 to 50,000 per second. In the strong stirring step, graphene is peeled off using a high shear mixer, thereby making it possible to dissolve stacks between graphene. As the high shear mixer, a thin film rotation type, a rotor/stator type, or a media mill type is preferably used, and examples thereof include "Filmix" (registered trademark) 30-30 type (Primix Corporation), "Clearmix" (registered trademark) CLM-0.8S (M Technique Co., Ltd.), "Labostar" (registered trademark) Mini LMZ015 (Ashizawa Finetech Co., Ltd.), and Super Shear Mixer SDRT0.35-0.75 (Satake Chemical Machinery Co., Ltd.).

As described above, the shear rate in the strong stirring step is preferably 5,000 to 50,000 per second. By setting the shear rate at 5,000 or more per second, the exfoliation of graphene is promoted, and the crystallite size calculated from the half-width of the peak corresponding to the (002) plane of graphene using Scherrer's formula can be easily adjusted to within the aforementioned range.

<Heat-resistant resin having nitrogen atom>
The resin composition of the present invention contains a heat-resistant resin having nitrogen atoms. By containing a heat-resistant resin, the heat resistance of the resin composition and the cured film can be improved. Furthermore, by the heat-resistant resin having nitrogen atoms, the dispersibility of graphene in the resin composition can be increased by the interaction between the nitrogen atoms in the heat-resistant resin and the nitrogen atoms on the graphene, and the conductivity of the cured film, particularly in a high-temperature environment, can be improved by a small amount of graphene. Here, the heat-resistant resin in the present invention refers to a resin in which, when a sample after heat treatment at 200°C for 30 minutes in an argon atmosphere is subjected to thermogravimetric analysis, the weight loss when the sample is heated from 25°C to 300°C at a heating rate of 10°C/min in an air atmosphere and held at 300°C for 30 minutes is less than 3 wt%, and the melting point does not appear below 300°C in the DSC curve obtained when the sample is heated from 25°C to 330°C at a rate of 10°C/min when differential scanning calorimetry is performed.

The heat-resistant resin having nitrogen atoms is preferably a thermosetting resin, and examples thereof include polyimide resins, polybenzimidazole resins, epoxy resins having nitrogen atoms, copolymers thereof, and copolymers of these with other copolymerization components. Two or more of these may be included. Among these, polyimide resins are preferred from the viewpoints of heat resistance and improving the dispersibility of graphene in the resin composition.

The resin composition of the present invention may also contain resins other than the heat-resistant resin, but the smaller the content, the better. Specifically, the solid content of resins other than the heat-resistant resin is preferably 20 parts by weight or less, more preferably 10 parts by weight or less, and even more preferably 5 parts by weight or less, per 100 parts by weight of the solid content of all resin components in the resin composition.

The resin composition of the present invention may further contain a crosslinking agent, which can further improve the strength of the cured film and the adhesion to the substrate. Examples of crosslinking agents include epoxy compounds, polyfunctional amine compounds, alcohol compounds, and silica compounds. Two or more of these may be included.

The resin composition of the present invention may further contain a solvent. Examples of the solvent include amide-based solvents such as NMP, dimethylacetamide, and dimethylformamide, sulfur-based solvents such as dimethylsulfoxide and sulfolane, ether-based solvents such as tetrahydrofuran and dioxane, ketone-based solvents such as cyclohexanone and methyl ethyl ketone, and solvents with high dielectric constants such as gamma-butyrolactone and acetonitrile. Two or more of these may be included.

<Method of producing resin composition>
Examples of the method for producing the resin composition of the present invention include a method of mixing the graphene, heat-resistant resin, solvent, and other components as necessary. Graphene may be mixed as a powder, but from the viewpoint of further improving the dispersibility of graphene in the resin composition, it is preferable to mix graphene dispersed in a solvent with other components. As a mixing device, a device capable of applying a shear force is preferable, and examples thereof include a planetary mixer, "Filmix" (registered trademark) (manufactured by Primix Corporation), and a planetary mixer.

<Cured film>
Next, the cured film of the present invention will be described. The cured film of the present invention can be obtained by forming a film from the above-mentioned resin composition and curing it.

Curing methods include, for example, curing by heating or curing by exposure to ultraviolet light.

The present invention will be explained below using examples. First, the evaluation methods used in each example and comparative example are shown below.

[Measurement Example 1] Measurement of N/C ratio and O/C ratio by X-ray photoelectron spectroscopy The graphene powder obtained by removing the solvent from the graphene dispersion used in each Example and Comparative Example by freeze-drying was subjected to X-ray photoelectron spectroscopy using an X-ray photoelectron spectrometer Quantera SXM (manufactured by Ulvac-PHI Co., Ltd.), and the C1s main peak based on carbon atoms was assigned to 284.3 eV, the O1s peak based on oxygen atoms was assigned to a peak near 533 eV, and the N1s peak based on nitrogen atoms was assigned to a peak near 402 eV, and the O/C ratio and N/C ratio were calculated from the area ratio of each peak. The N/C ratio was calculated to the third decimal place by rounding off the fourth decimal place, and the O/C ratio was calculated to the second decimal place by rounding off the third decimal place. The analysis conditions and data processing conditions were as follows.
<Analysis conditions>
Excitation X-ray: Monochromatic AlKα1,2 radiation (1486.6 eV)
X-ray diameter: 200 μm
Photoelectron detection angle (tilt of detector relative to sample surface): 45°
<Data processing conditions>
Smoothing: 9-point smoothing
Horizontal axis correction: C1s main peak was set to 284.3 eV.

[Measurement Example 2] X-ray diffraction measurement Graphene powder obtained by removing the solvent from the graphene dispersion liquid used in each of the Examples and Comparative Examples by freeze-drying was vacuum-dried at 60°C for 12 hours, and then X-ray diffraction measurement was performed under the following conditions using an X-ray diffractometer D8 ADVANCE (manufactured by Bruker Corporation). The crystallite size was calculated using the Scherrer formula from the half-width of the peak (around 2θ/θ=25°) corresponding to the (002) plane of the graphene crystal.
<Analysis conditions>
Scanning range: 5° to 50°
Step size: 0.016°
Scanning speed: 1 step/sec.

[Measurement Example 3] Measurement of the size of graphene in the plane direction by SEM observation After the graphene dispersion used in each Example and Comparative Example was diluted to 0.01 wt%, the sample was dropped onto a mica substrate and dried, and then magnified and observed using a scanning electron microscope S-5500 (manufactured by Hitachi High-Tech Corporation) at a magnification such that the graphene fits within an appropriate field of view. The longest and shortest diameters of 10 randomly selected graphenes were measured, and the size of each graphene in the plane direction was calculated from the average value, and the arithmetic average value was calculated to determine the size of the graphene in the plane direction.

[Measurement Example 4] Evaluation of Dispersibility The cured films obtained in each of the Examples and Comparative Examples were heat-treated in an air atmosphere at a temperature of 300°C for 30 minutes, and then, using an ECLIPSE L200N (manufactured by Nikon Instech Co., Ltd.), under conditions of an eyepiece: ×10 magnification, and an objective lens: ×10 magnification, for five randomly selected visual fields, aggregates having an average of the longest and shortest diameters of 20 μm or more were counted among the aggregates observed in each visual field, and the average value of the five visual fields was calculated and rounded off to the first decimal place to obtain the number of aggregates. Dispersibility was evaluated as ○ when the number of aggregates was 10 or less, as △ when the number was 11 to 30, and as × when the number was 31 or more.

[Measurement Example 5] Evaluation of heat resistance Approximately 10 mg of the cured film obtained in each Example and Comparative Example was weighed out and placed on an aluminum pan, and the film was heated from 25° C. to 300° C. at a rate of 10° C./min in an air atmosphere using a TG/DTA6200 (manufactured by Seiko Instruments Inc.), and then held at 300° C. for 30 minutes, and the weights before and after heating were measured. The weight loss [%] was calculated by {(weight before heating-weight after heating)/weight before heating}×100.

On the other hand, about 10 mg of the cured film obtained in each Example and Comparative Example was weighed out and sealed in an aluminum sealed pan, and a thermogravimetric analysis was performed by heating from 25°C to 330°C at a rate of 10°C/min using a DSC6200 (Seiko Instruments Inc.), and a DSC curve was obtained. The presence or absence of a melting peak was observed from the obtained DSC curve, and the melting point was determined.

If the weight loss was less than 3% by weight and the melting point did not appear below 300°C, the heat resistance was rated as good; otherwise, the heat resistance was rated as bad.

[Measurement Example 6] Evaluation of electrical conductivity in a high-temperature environment The cured films obtained in each of the Examples and Comparative Examples were heat-treated in an air atmosphere at a temperature of 300°C for 30 minutes, and then the sheet resistance was calculated using a "Loresta" (registered trademark) GP (MCP-T610) (manufactured by Mitsubishi Chemical Analytech Co., Ltd.). In addition, the thickness of the portion where the sheet resistance was calculated was measured using a micrometer MDH-25MB (manufactured by Mitutoyo Corporation). The volume resistivity was calculated from the product of the obtained sheet resistance and the thickness, and the electrical conductivity in a high-temperature environment was evaluated.

Measurement Example 7: Evaluation of Adhesion to Substrate in High-Temperature Environment The laminate of the glass substrate and the cured film obtained in each Example and Comparative Example was heat-treated in an air atmosphere at a temperature of 300°C for 30 minutes, and then the adhesion to the substrate was evaluated by a cross-cut method. Specifically, 11 cuts were made in the lengthwise and widthwise directions of the cured film on the glass substrate, each cut at intervals of 1 mm until the substrate was reached, to provide 100 checkered regions of 1 ^mm2 . Cellotape (registered trademark) CT-15 (manufactured by Nichiban Co., Ltd., width 15 mm, length 2 cm) was attached to the checkered regions so as not to trap air bubbles, and the tape was peeled off in a direction perpendicular to the surface of the glass substrate, and the number of checkered regions of 1 ^mm2 remaining on the glass substrate was counted to evaluate the adhesion to the substrate.

[Synthesis Example 1] Preparation of graphene oxide gel Using 1500 mesh natural graphite powder (manufactured by Shanghai Yifan Graphite Co., Ltd.) as a raw material, 220 ml of 98% concentrated sulfuric acid, 5 g of sodium nitrate, and 30 g of potassium permanganate were added to 10 g of natural graphite powder in an ice bath, and the temperature of the mixture was kept below 20 ° C. while mechanically stirring for 1 hour. The mixture was removed from the ice bath and stirred in a 35 ° C. water bath for 4 hours, and then 500 ml of ion-exchanged water was added to obtain a suspension, which was stirred at 90 ° C. for another 15 minutes. Finally, 600 ml of ion-exchanged water and 50 ml of hydrogen peroxide were added and stirred for 5 minutes to obtain a graphene oxide dispersion. This was filtered while hot, and metal ions were washed with a dilute hydrochloric acid solution, and acid was washed with ion-exchanged water. The graphene oxide gel was prepared by repeating washing until the pH reached 7. The elemental ratio of oxygen atoms to carbon atoms of the prepared graphene oxide gel measured by X-ray photoelectron spectroscopy was 0.53.

[Synthesis Example 2] Preparation of Surface-Treated Graphene Dispersion-1 The graphene oxide gel prepared in Synthesis Example 1 was diluted to a concentration of 30 mg/ml using ion-exchanged water, and treated for 30 minutes using an ultrasonic cleaner to obtain a uniform graphene oxide dispersion. 20 ml of the obtained graphene oxide dispersion was mixed with 0.3 g of dopamine hydrochloride as a surface treatment agent, and treated for 60 minutes at a rotation speed of 3,000 rpm using a Homo Disper 2.5 type (manufactured by Primix Corporation). The graphene oxide dispersion after the treatment was subjected to ultrasonic waves at an output of 300 W for 30 minutes (micro-refining process) using an ultrasonic device UP400S (manufactured by Hielscher Corporation). The graphene oxide dispersion obtained by the micro-refining process was diluted to 5 mg/ml using ion-exchanged water, and 0.3 g of sodium dithionite was added to 20 ml of the diluted dispersion, and a reduction reaction was carried out for 1 hour while stirring at 40 ° C. Thereafter, the mixture was filtered using a reduced pressure suction filter, and then the washing step of diluting the mixture with water to 0.5% by weight and filtering by suction was repeated five times to obtain an aqueous dispersion of surface-treated graphene.

The obtained surface-treated graphene aqueous dispersion was diluted with N-methylpyrrolidone (NMP) to a concentration of 0.5% by weight, and treated with a "Filmix" (registered trademark) 30-30 model (manufactured by Primix Corporation) at a rotation speed of 40 m/s (shear rate: 20,000 per second) for 60 seconds (strong stirring process). After treatment, the solvent was removed by vacuum suction filtration. To further remove water, the solution was diluted with NMP to a concentration of 0.5% by weight, treated with a Homo Disper 2.5 model (manufactured by Primix Corporation) at a rotation speed of 3,000 rpm for 30 minutes, and vacuum suction filtration were repeated twice, and then diluted with NMP to a concentration of 1.5% by weight to obtain surface-treated graphene dispersion-1.

[Synthesis Example 3] Preparation of surface-treated graphene dispersion-2 A surface-treated graphene dispersion-2 was obtained in the same manner as in Synthesis Example 2, except that 0.3 g of 2-phenylethylamine (PEA) was used as the surface treatment agent.

[Synthesis Example 4] Preparation of Surface-Treated Graphene Dispersion-3 A surface-treated graphene dispersion-3 was obtained in the same manner as in Synthesis Example 2, except that 0.3 g of benzylamine was used as the surface treatment agent.

[Synthesis Example 5] Preparation of Surface-Treated Graphene Dispersion-4 A surface-treated graphene dispersion-4 was obtained in the same manner as in Synthesis Example 2, except that the amount of sodium dithionite added was changed to 0.01 g.

Synthesis Example 6 Preparation of Surface-Treated Graphene Dispersion-5 A surface-treated graphene dispersion-5 was obtained under the same conditions as in Synthesis Example 2, except that 0.05 g of dopamine hydrochloride was used as the surface treatment agent.

Synthesis Example 7 Preparation of Surface-Treated Graphene Dispersion-6 A surface-treated graphene dispersion-6 was obtained under the same conditions as in Synthesis Example 2, except that 1.0 g of dopamine hydrochloride was used as the surface treatment agent.

[Synthesis Example 8] Preparation of Surface-Treated Graphene Dispersion-7 Graphene powder ("XGNP" (registered trademark) R10 manufactured by XGScience Corporation) was diluted to a concentration of 30 mg/ml using ion-exchanged water, and treated for 30 minutes using an ultrasonic cleaner to obtain a graphene aqueous dispersion. 20 ml of the obtained graphene dispersion was mixed with 0.3 g of dopamine hydrochloride as a surface treatment agent, and treated for 60 minutes at a rotation speed of 3,000 rpm using a Homo Disper 2.5 type (manufactured by Primix Corporation). Thereafter, the mixture was filtered using a vacuum suction filter, and then freeze-dried to obtain surface-treated graphene. NMP was added to the obtained surface-treated graphene so that the solid content concentration was 1.5 wt%, and the mixture was treated for 60 minutes at a rotation speed of 3,000 rpm using a Homo Disper 2.5 type (manufactured by Primix Corporation) to obtain surface-treated graphene dispersion-7.

[Synthesis Example 9] Preparation of Surface-Treated Graphene Dispersion-8 A surface-treated graphene dispersion-8 was obtained in the same manner as in Synthesis Example 8, except that 0.3 g of 2-phenylethylamine (PEA) was used as the surface treatment agent.

Synthesis Example 10 Preparation of Graphene Dispersion A graphene dispersion was obtained in the same manner as in Synthesis Example 2, except that no surface treatment agent was used.

Synthesis Example 11 Preparation of Surface-Treated Graphene Dispersion-9 A surface-treated graphene dispersion-9 was obtained under the same conditions as in Synthesis Example 2, except that ultrasonic waves were applied for 20 minutes at an output of 300 W using an ultrasonic device UP400S (manufactured by Hielscher Corporation).

Synthesis Example 12 Preparation of Surface-Treated Graphene Dispersion-10 A surface-treated graphene dispersion-10 was obtained under the same conditions as in Synthesis Example 2, except that ultrasonic waves were applied for 90 minutes at an output of 300 W using an ultrasonic device UP400S (manufactured by Hielscher Corporation).

[Synthesis Example 13] Preparation of Surface-Treated Graphene Dispersion-11 A surface-treated graphene dispersion-11 was obtained under the same conditions as in Synthesis Example 2, except that ultrasonic waves were applied for 2 minutes at an output of 300 W using an ultrasonic device UP400S (manufactured by Hielscher Corporation).

[Synthesis Example 14] Preparation of polyamideimide / butadiene copolymer solution In a reaction vessel, 192 g of trimellitic anhydride (TMA) (Tokyo Chemical Industry Co., Ltd. product number C0046), 250 g of diphenylmethane diisocyanate (MDI) (Tokyo Chemical Industry Co., Ltd. product number D0897), 70 g of carboxyl group-terminated acrylonitrile-butadiene rubber (Nipol (registered trademark) LX511A manufactured by Nippon Zeon Co., Ltd.) (rubber component) and 541 g of NMP were charged, and the mixture was heated and stirred at 120 ° C. for about 1 hour, and then heated to 170 ° C. and heated and stirred for 5 hours to carry out a polymerization reaction. While cooling, NMP was further added to obtain a polymer solution with a solid content concentration of 20 wt%.

[Example 1]
A resin composition was obtained by adding 6 parts by weight of the surface-treated graphene dispersion-1 (1.5% by weight) prepared in Synthesis Example 2 as the conductive material in terms of graphene solid content, and 100 parts by weight of an NMP solution (21% by weight) of a polyimide resin ("Semicofine" (registered trademark) SP-453 manufactured by Toray Industries, Inc.) in terms of polyimide solid content as the heat-resistant resin, and stirring at 2000 rpm for 5 minutes with a planetary mixer. The obtained resin composition was coated on a glass substrate and heat-treated at 200°C for 1 hour in an argon atmosphere to obtain a cured film having a thickness of 50 μm.

[Example 2]
A resin composition and a cured film were prepared under the same conditions as in Example 1, except that the surface-treated graphene dispersion-2 (1.5 wt%) prepared in Synthesis example 3 was used as the conductive material.

[Example 3]
A resin composition and a cured film were prepared under the same conditions as in Example 1, except that the surface-treated graphene dispersion-3 (1.5 wt%) prepared in Synthesis example 4 was used as the conductive material.

[Example 4]
A resin composition and a cured film were prepared under the same conditions as in Example 1, except that the surface-treated graphene dispersion-7 (1.5 wt%) prepared in Synthesis example 8 was used as the conductive material.

[Example 5]
A resin composition and a cured film were prepared under the same conditions as in Example 1, except that the surface-treated graphene dispersion-4 (1.5 wt%) prepared in Synthesis example 5 was used as the conductive material.

[ Reference Example 1 ]
A resin composition and a cured film were prepared under the same conditions as in Example 1, except that the surface-treated graphene dispersion-8 (1.5 wt%) prepared in Synthesis example 9 was used as the conductive material.

[Example 7]
A resin composition and a cured film were prepared under the same conditions as in Example 1, except that 3 parts by weight of the surface-treated graphene dispersion-1 (1.5 wt%) prepared in Synthesis example 2 was added as the conductive material, in terms of graphene solid content.

[Example 8]
A resin composition and a cured film were prepared under the same conditions as in Example 1, except that 1.5 parts by weight of the surface-treated graphene dispersion-1 (1.5 wt%) prepared in Synthesis example 2 was added as the conductive material, in terms of graphene solid content.

[Example 9]
A resin composition and a cured film were prepared under the same conditions as in Example 1, except that the surface-treated graphene dispersion-9 (1.5 wt%) prepared in Synthesis example 11 was used as the conductive material.

[Example 10]
A resin composition and a cured film were prepared under the same conditions as in Example 1, except that the surface-treated graphene dispersion-10 (1.5 wt%) prepared in Synthesis example 12 was used as the conductive material.

[Example 11]
A resin composition and a cured film were prepared under the same conditions as in Example 1, except that the surface-treated graphene dispersion-11 (1.5 wt%) prepared in Synthesis example 13 was used as the conductive material.

[Comparative Example 1]
A resin composition and a cured film were prepared under the same conditions as in Example 1, except that 6 parts by weight of the surface-treated graphene dispersion-5 (1.5 wt%) prepared in Synthesis example 6 was added as the conductive material, in terms of graphene solid content.

[Comparative Example 2]
A resin composition and a cured film were prepared under the same conditions as in Example 1, except that 6 parts by weight of the surface-treated graphene dispersion-6 (1.5 wt%) prepared in Synthesis example 7 was added as the conductive material, in terms of graphene solid content.

[Comparative Example 3]
A resin composition and a cured film were prepared under the same conditions as in Example 1, except that the graphene dispersion prepared in Synthesis Example 10 was used as the conductive material.

[Comparative Example 4]
A resin composition and a cured film were prepared under the same conditions as in Example 1, except that an NMP solution (20% by weight) of polyether ether ketone resin (PEEK) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product number 23969-50) was used as the heat-resistant resin not having nitrogen atoms.

[Comparative Example 5]
A resin composition and a cured film were prepared under the same conditions as in Example 1, except that a NMP solution (10% by weight) of a polyamide resin having a melting point of 300° C. or less ("AQ Nylon" (registered trademark) P-70 manufactured by Toray Industries, Inc.) was used as the resin component.

[Comparative Example 6]
A resin composition and a cured film were prepared under the same conditions as in Example 1, except that an NMP solution (50 wt%) of polyvinyl alcohol resin (PVA) (Sigma-Aldrich Corporation, product number 348406) having a weight loss of 3 wt% or more at 300°C was used as the resin component.

[Comparative Example 7]
A resin composition and a cured film were prepared under the same conditions as in Example 1, except that CNT (multi-walled carbon nanotubes manufactured by Sigma-Aldrich Corporation, product number 698849: diameter 6-13 nm, length 2.5-20 μm) was used as the conductive material.

[Comparative Example 8]
A resin composition and a cured film were prepared under the same conditions as in Example 1, except that 6 parts by weight of acetylene black ("Denka Black" (registered trademark) manufactured by Denka Company Ltd.) was used as the conductive material.

[Comparative Example 9]
A resin composition and a cured film were prepared under the same conditions as in Example 1, except that 6 parts by weight of acetylene black ("Denka Black" (registered trademark) manufactured by Denka Company Ltd.) in powder form was used as the conductive material, and 100 parts by weight of an NMP solution (20% by weight) of the polyamideimide/butadiene copolymer having a weight loss of 3% by weight or more at 300° C. prepared in Synthesis Example 14 was used as the resin component.

[Comparative Example 10]
A resin composition and a cured film were prepared under the same conditions as in Example 1, except that CNT (multi-walled carbon nanotubes manufactured by Sigma-Aldrich Corporation, product number 69849: diameter 6-13 nm, length 2.5-20 μm) were used as the conductive material, 70 parts by weight of an NMP solution (21% by weight) of a polyimide resin (manufactured by Toray Industries, Inc., "Semicofine" (registered trademark) SP-453) was used as the heat-resistant resin in terms of polyimide solids, and 30 parts by weight of an NMP solution (30% by weight) of a polyvinyl butyral resin (manufactured by Sekisui Chemical Co., Ltd., "S-LEC" (registered trademark) BM-2) having a weight loss of 3% or more at 300° C. was used as the resin component.

The details and evaluation results of each example and comparative example are shown in Tables 1 and 2.

Claims (5)

A resin composition comprising graphene and a heat-resistant resin having nitrogen atoms,
the graphene has an atomic ratio of nitrogen to carbon (N/C ratio) of 0.005 or more and 0.030 or less, and an atomic ratio of oxygen to carbon (O/C ratio) of 0.08 or more and 0.30 or less, as measured by X-ray photoelectron spectroscopy;
a heat-resistant resin having nitrogen atoms, which, when subjected to a heat treatment at 200°C for 30 minutes in an argon atmosphere and then subjected to a thermogravimetric analysis, loses less than 3% by weight when heated from 25°C to 300°C at a heating rate of 10°C/min in an air atmosphere and maintained at 300°C for 30 minutes; and which, when subjected to a differential scanning calorimetry measurement, does not exhibit a melting point at or below 300°C in a DSC curve obtained when the temperature is raised from 25°C to 330°C at a rate of 10°C/min;
A resin composition having a graphene content of 1 part by weight or more and 30 parts by weight or less based on 100 parts by weight of a heat-resistant resin having a nitrogen atom . The resin composition according to claim 1, wherein the heat-resistant resin having nitrogen atoms includes a polyimide resin. The resin composition according to claim 1 or 2, wherein the graphene has a crystallite diameter of 2 nm or less, calculated by Scherrer's formula from a peak corresponding to the (002) plane of the graphene crystal in an X-ray diffraction measurement. The resin composition according to any one of claims 1 to 3 , wherein the size of the graphene in a planar direction is 0.5 µm or more and 5 µm or less. A cured film of the resin composition according to any one of claims 1 to 4 .