JP5969905B2 - Method for producing alignment film of thin layer graphite or thin layer graphite compound - Google Patents

Description

  The present invention relates to a method for producing an alignment film of a thin layer graphite or a thin layer graphite compound.

  Graphene, the basis of the crystal structure of graphite (graphite), is a two-dimensional planar crystal consisting of an infinite number of carbon six-membered rings. From its unique crystal structure, excellent electrical properties, mechanical properties, thermal properties, It exhibits optical properties and chemical stability, and is expected to be applied to various fields such as next-generation high-speed electronic devices, transparent electrodes, power storage devices, and structural materials.

  Thin-layer graphite refers to one having a structure in which 1 to several tens of graphene layers are laminated. The thin-layer graphite compound refers to an intercalation compound in which an electron donor or an electron acceptor is inserted between the thin-layer graphite layers, or a compound in which a functional group is chemically bonded to the thin-layer graphite.

  These thin-layer graphites and thin-layer graphite compounds are considered to have properties equivalent to, but not equivalent to, the electrical properties, mechanical properties, thermal properties, optical properties, and chemical stability of single-layer graphene.

  As applications of thin-layer graphite and thin-layer graphite compounds, there are high expectations for transparent electrodes and conductive films in consideration of light transmittance and electrical characteristics.

  As a method for producing a conductive film of thin-layer graphite or a thin-layer graphite compound, Patent Document 1 discloses a method for producing a thin film of thin-layer graphite by applying and drying a dispersion containing thin-layer graphite directly peeled off and purified from graphite. A method is disclosed.

  In Non-Patent Document 1, a thin-layer graphite compound thin film is manufactured by applying a reduction liquid containing a thin-layer graphite oxide obtained by exfoliating and synthesizing graphite oxide obtained by strong oxidation to a substrate and then performing a reduction treatment. A method is disclosed.

  Patent Documents 2 and 3 disclose a method for producing a thin graphite film by chemical vapor deposition.

JP 2011-184264 A Special table 2008-50228 gazette JP 2012-162442 A

Monthly Display, Vol. 18, no. 1, P67, 2011

  Thin-layer graphite and thin-layer graphite compounds have large anisotropy of conductivity due to their structures, and there is a difference of about two digits between the conductivity in the layer surface direction and the conductivity in the direction perpendicular to the layer surface. Therefore, in order to obtain a low-resistance transparent electrode or conductive film, it is necessary to orient the thin graphite or thin graphite compound particles in the plane direction of the transparent electrode or conductive film.

  In the methods of Patent Document 1 and Non-Patent Document 1, since agglomeration occurs partially when the dispersion is dried, it is difficult to obtain a uniform alignment film, and the resistance of the film tends to increase.

  Further, in the chemical vapor deposition method described in Patent Document 2, an expensive apparatus is necessary, or a thin graphite film is once formed on the surface of a catalyst metal such as copper, and then transferred to a transparent plastic substrate. Therefore, the process is complicated and the manufacturing cost is increased.

  An object of the present invention is to provide a method capable of easily producing an oriented film in which thin-layer graphite or a thin-layer graphite compound is uniformly oriented.

According to the present invention,
Using one or more selected from the group consisting of thin layer graphite and thin layer graphite compound as a raw material, adding a dispersion in which the raw material is dispersed in an organic solvent to water, and redispersing the raw material in water By having an alignment film deposition step of depositing the alignment film of the raw material on the surface of water,
Here, as the organic solvent, an organic solvent having a specific gravity at room temperature of less than 1.0 is used.
As the dispersion, there is provided a method for producing an alignment film, wherein a dispersion having a mass of the raw material of 0.0001 to 0.05 g / ml with respect to the volume of the organic solvent is used.

  This method may further include a step of drying and heat-treating the deposited alignment film on the heat-resistant substrate after the alignment film deposition step.

  The present invention provides a method capable of easily producing an alignment film in which thin-layer graphite or a thin-layer graphite compound is uniformly oriented.

It is a figure for demonstrating one form of the manufacturing process of alignment film. It is a figure for demonstrating the deposition principle of alignment film. 2 is a photograph of the graphite compound alignment film obtained in Example 1. FIG. 2 is an electron micrograph of a graphite compound alignment film obtained in Example 1. FIG. It is a figure which shows the slide glass for resistance measurements. 3 is an electron micrograph of a graphite alignment film obtained in Example 4.

  The raw material used in the present invention may be either a thin layer graphite or a thin layer graphite compound. Only one type of thin-layer graphite can be used as a raw material, or only one type of thin-layer graphite compound can be used. Also, two or more types of thin-layer graphite can be used, or two or more types of thin-layer graphite compounds can be used. One or two or more types of thin-layer graphite and one or two or more types of thin-layer graphite compounds may be used in combination. That is, one or more selected from the group consisting of thin-layer graphite and thin-layer graphite compounds can be used as a raw material.

  In addition, the thickness (thickness in the layer direction) of the thin layer graphite and the thin layer graphite compound is, for example, 100 nm or less.

  An organic solvent having a specific gravity of less than 1.0 is used as an organic solvent of a dispersion in which raw materials are dispersed in an organic solvent (hereinafter sometimes referred to as a raw material dispersion). The specific gravity is preferably less than 0.9, and more preferably less than 0.8. When the specific gravity is 1.0 or less, it is possible to easily prevent the alignment film from easily depositing on the surface of water and precipitating or dispersing the raw material in water. The specific gravity here is the specific gravity at room temperature (typically 25 ° C.) (the reference material is also water at that room temperature).

  The ratio of the mass of the raw material to the volume of the organic solvent in the raw material dispersion is 0.0001 to 0.05 g / ml. When the amount is 0.0001 g / ml or more, it is possible to easily prevent the dripping amount of the raw material dispersion from increasing and the oil film deposited on the surface (the oil film will be described later) from becoming thick, and to prevent reaggregation of the raw material easily. It is easy to obtain a uniform alignment film. Further, if it is 0.05 g / ml or less, preferably 0.02 g / ml or less, it is easy to re-disperse the raw material in water, it is possible to easily prevent the formation of aggregates, and a uniform alignment film is obtained. Is easy.

  One form of the manufacturing process of the alignment film of this invention is shown in FIG. The alignment film 3 can be obtained on the surface of the water by a simple technique of dropping the raw material dispersion 2 into the water 1 and then stirring and dispersing (redispersing) the raw material in water. Stirring may be performed as necessary. For example, when ethanol is used as the organic solvent, the raw material may be redispersed in water without stirring.

  Although the deposition principle of the alignment film is not necessarily clarified, it is considered that the deposition is performed based on the principle shown in FIG. After the raw material particles 4 covered with the organic solvent 5 are monodispersed in the water 1, they float on the surface of the water like lotus leaf-like ice. An oil film 6 (organic solvent film) containing raw material particles arranged in a monodispersed state on the surface of water is formed. After the formation of the oil film, the organic solvent evaporates, or the organic solvent dissolves in water almost simultaneously with the formation of the oil film, so that only the raw alignment film 7 is deposited.

  According to the present invention, the alignment film of the raw material can be easily and efficiently produced by a simple method of adding the raw material dispersion to water (for example, dropping) and stirring as necessary. Therefore, it is possible to easily produce an alignment film of thin-layer graphite and / or thin-layer graphite compound having excellent electrical conductivity, transparency, mechanical properties, and the like.

  The method of the present invention may further include a step of performing drying and heat treatment after the substrate is pulled up to the heat resistant substrate. As a result, a raw alignment film is obtained in a state of being attached to the substrate. That is, an alignment film with a substrate can be obtained. For example, the alignment film deposited on the surface of water can be easily pulled up to a glass substrate or the like. If necessary, the alignment film can be dried, that is, the organic solvent or water can be removed by evaporation. Furthermore, heat treatment can be performed after drying.

  Next, examples of the present invention will be described, but the present invention is not limited to the following examples. In addition, operation in each Example was performed under normal temperature and a normal pressure (25 degreeC, 0.10 MPa) unless there is particular description.

Example 1
A thin layer graphite compound (manufactured by Bridgestone CB, trade name: WGNP) was used as a raw material. 20 mg of raw material and 10 ml of hexane were put into a screw tube (24 mmφ (diameter) × 50 mm), and a thin layer graphite compound was dispersed by ultrasonic treatment for 5 minutes to obtain a raw material dispersion (raw material mass of raw material dispersion / organic solvent (Volume ratio: 0.002 g / ml).

  0.2 ml of the raw material dispersion was dropped into 100 ml of ion-exchanged water in a 100 ml beaker using a pipette. The raw material dispersion became oil droplets on the surface of the ion exchange water, and the thin graphite compound was in an aggregated state. Thereafter, ion-exchanged water was stirred with a shell and the raw material dispersion was redispersed in water. Stirring was continued, and after a while, an almost uniform gray and translucent film was deposited on the surface of water. The membrane was pulled up on a slide glass (26 mm × 76 mm × 1 mm thickness) and dried at room temperature. FIG. 3 shows a photograph of the film formed on the slide glass. Further, as a result of observing the fine structure of this film with an electron microscope (FIG. 4), it was confirmed that most of the particles were arranged flat and the film had high orientation.

(Example 2) Measurement of resistance of alignment film As shown in FIG. 5, an alignment film was formed on a glass slide 9 on which a silver electrode 8 was formed in the same manner as in Example 1, and a general-purpose digital multimeter was used. Resistance measurement was performed by the terminal method. The resistance was measured after film formation, and the same sample was subjected to heat treatment at 250 ° C. for 1 hour in air, then further subjected to heat treatment at 500 ° C. for 1 hour in air, and then further subjected to heat treatment at 500 ° C. for 1 hour in air. went. Table 1 shows the results. Compared with immediately after the film formation, those subjected to heat treatment tended to have lower resistance. This is presumably because water, hydroxyl groups, and the like remaining between the particles and between the particles and the electrode are eliminated by the heat treatment, and the adhesion is improved and the contact resistance is reduced. In addition, the reason why the resistance is increased by the final heat treatment at 500 ° C. × 1 hour is considered to be that a part of carbon disappears due to oxidation.

(Example 3)
As a raw material, a thin layer graphite compound (trade name: WGNP, manufactured by Bridgestone CB Corp.) was used. Except for this, film formation and resistance measurement were performed in the same manner as in Example 2. The obtained film showed light transmittance equivalent to that of Example 1. Table 1 shows the measured resistance values. A value about one digit lower than that of Example 2 was obtained. This is considered to be due to the improvement in the electrical conductivity of the particles themselves due to the thinning of the layers, and the effect that the adhesion between the particles was improved along with the thinning of the layers and the contact resistance was reduced.

  The thinning process performed here is a method proposed in Japanese Patent Application No. 2012-149565 filed by the same applicant as the applicant of the present application, and the layers of graphite or graphite compounds are separated by a high-pressure emulsification method. A method for producing thin-layer graphite or a thin-layer graphite compound having a high-pressure emulsification treatment step. The principle of the high-pressure emulsification method is that high-pressure flow is generated by applying high pressure to the liquid containing the raw material and passing through a narrow gap (pore) called an emulsification nozzle, and the shearing force, grinding force, and impact force at that time , Emulsification, dispersion, homogenization and refinement by cavitation and the like.

  Specifically, the thinning process was performed as follows. 10 g of a raw material graphite compound (manufactured by Bridgestone CB, trade name: WGNP, layer thickness (thickness in the stacking direction) of 50 nm or less, average particle size in the plane direction of the layer) of 100 g in ethanol is added to pure water. The suspension was diluted with 900 ml to obtain a suspension having a raw material concentration of 1.01% by mass. This suspension was subjected to high-pressure emulsification treatment by passing it 10 times at an emulsification pressure of 200 MPa using a high-pressure emulsifier (trade name: DeBEE-2000, BEE International). At this time, a diamond nozzle having a hole diameter of 0.13 mm and a hole length of 7.5 mm was used as an emulsifying nozzle. Since the processing speed was about 300 ml / min, the flow rate of the suspension in the nozzle was calculated to be about 377 m / sec.

  In the suspension obtained after the high-pressure emulsification treatment, fine aggregates were generated, and the aggregates and the liquid phase were separated. Aggregates could be easily separated by suction filtration. This separated aggregate was used as a raw material in Example 3 (the above-described thinned graphite compound was thinned). In addition, when the dried aggregate particle was observed by SEM, it was confirmed that the particle was thinned. The formation of aggregates after high-pressure emulsification was thought to be due to thinning and refinement of particles. Moreover, it was confirmed that the aggregate particles are easily dispersed in an organic solvent such as ethanol.

Example 4
As a raw material, a thin-layer graphite (flaky graphite, manufactured by Ito Graphite Industries Co., Ltd., trade name: Z-5F) subjected to a thinning treatment by the same method as in Example 3 was used. Except for this, film formation and resistance measurement were performed in the same manner as in Example 2. A translucent film was obtained in the same manner as in Example 1. Table 1 shows the measured resistance values. The value was about one digit higher than that of Example 2. FIG. 6 shows an electron micrograph of the alignment film. Although it was confirmed that the particles were aligned in a flat manner and the orientation was high, the contour of the particles was clear and it was assumed that the layer thickness was thicker than the thickness of the thin graphite compound of Example 1. For this reason, it is considered that the resistance is higher than that of Example 1 because the conductivity of the particles themselves is low and the adhesion between the particles is relatively low.

(Example 5)
An alignment film was prepared in the same manner as in Example 2 except that the organic solvent of the raw material dispersion was changed to ethanol, and resistance measurement was performed. When the organic solvent was ethanol, unlike the hexane, when the raw material dispersion was dropped into water, a thin graphite compound was deposited on the surface of water almost simultaneously. This is presumably because ethanol is a water-soluble solvent, and ethanol dissolves in water almost at the same time as the thin graphite compound covered with ethanol floats on the water surface. The obtained alignment film had almost the same light transmittance as that of Example 1. Table 1 shows the measured resistance values. The resistance was almost the same as in Example 1, and it was considered that a similar alignment film was obtained.

(Example 6)
Except that the raw material mass / organic solvent volume ratio in the raw material dispersion was changed to 0.02 g / ml, the same method as in Example 1 was carried out. The observation result of the obtained film with an electron microscope was the same as in Example 1. Most particles were lined up flat.

(Comparative Example 1)
Film formation was attempted in the same manner as in Example 1 except that N-methylpyrrolidone was used as the organic solvent for the raw material dispersion. However, no alignment film was obtained, and the thin graphite compound was dispersed in water.

(Comparative Example 2)
The same procedure as in Example 1 was performed except that the raw material mass / organic solvent volume ratio in the raw material dispersion was changed to 0.10 g / ml. A large amount of aggregates were generated during dispersion in water, and a uniform alignment film could not be obtained.

Claims (2)

Using one or more selected from the group consisting of thin layer graphite and thin layer graphite compound as a raw material, adding a dispersion in which the raw material is dispersed in an organic solvent to water, and redispersing the raw material in water By having an alignment film deposition step of depositing the alignment film of the raw material on the surface of water,
Here, as the organic solvent, an organic solvent having a specific gravity at room temperature of less than 1.0 is used.
A method for producing an alignment film, wherein a dispersion having a mass of the raw material of 0.0001 to 0.05 g / ml with respect to the volume of the organic solvent is used as the dispersion.   The method according to claim 1, further comprising a step of drying and heat-treating the deposited alignment film on the heat-resistant substrate after the alignment film deposition step.