WO2020195328A1 - Method for producing nanodiamond dispersion composition, and nanodiamond dispersion composition - Google Patents

Abstract

Provided are: a method for producing a nanodiamond dispersion composition which has excellent dispersibility of nanodiamond particles in a dispersion medium while preventing the inflow of zirconia beads; and a nanodiamond dispersion composition obtained by said method.　A method for producing a nanodiamond dispersion composition according to the present invention comprises: a preparation step in which a crude nanodiamond product is obtained by the detonation process; an oxidation treatment step in which an oxidizing agent is used to remove graphite from the crude nanodiamond product obtained in the preparation step; and an in-liquid plasma treatment step in which nanodiamond, which has been subjected to the oxygen treatment step, is subjected to plasma treatment in a liquid, and dispersed.

Description

Method for producing nanodiamond dispersion composition and nanodiamond dispersion composition

The present invention relates to a method for producing a nanodiamond dispersion composition and a nanodiamond dispersion composition. More specifically, the present invention relates to a method for producing a nanodiamond dispersion composition and a nanodiamond dispersion composition obtained by the production method. The present application claims the priority of Japanese Patent Application No. 2019-058006 filed in Japan on March 26, 2019, the contents of which are incorporated herein by reference.

It is known that nano-sized fine substances have new properties that cannot be expressed in the bulk state. For example, nanodiamond particles (= nano-sized diamond particles) have mechanical strength, high refractive index, thermal conductivity, insulating property, antioxidant property, and an action of promoting crystallization of a resin or the like. However, since nanodiamond particles generally have a large proportion of surface atoms, the sum of van der Waals forces that can act between the surface atoms of adjacent particles is large, and agglutination is likely to occur. In addition to this, in the case of nanodiamond particles, a phenomenon called agglutination can occur in which the Coulomb interaction between the crystal planes of adjacent crystal faces contributes and very strongly aggregates. Therefore, it has been very difficult to disperse the nanodiamond particles in the form of primary particles in an organic solvent or resin.

As a method for dispersing nanodiamond particles, for example, a method of preparing a nanodiamond suspension, adjusting the pH of the suspension, and then bead milling using zirconia beads or the like to crush it is known (patented). Reference 1).

Special Table 2016-501811

However, it was extremely difficult to prevent zirconia derived from zirconia beads from flowing into the nanodiamond dispersion composition by crushing by bead mill treatment using zirconia beads.

Therefore, an object of the present invention is a method for producing a nanodiamond dispersion composition having excellent dispersibility of nanodiamond particles in a dispersion medium while preventing the inflow of zirconia, and a nanodiamond dispersion composition obtained by the method. To provide.

As a result of diligent studies to achieve the above object, the present inventor removed graphite from the crude nanodiamond product produced by the detonation method using an oxidizing agent, and then subjected to submerged plasma treatment. We have found that nanodiamonds can be well dispersed without the use of zirconia beads. The present invention has been completed based on these findings.

That is, the present invention relates to a production step of obtaining a crude nanodiamond product by a roaring method, an oxidation treatment step of removing graphite from the crude nanodiamond product obtained in the above production step using an oxidizing agent, and the oxidation treatment step. Provided is a method for producing a nanodiamond dispersion composition, which comprises an in-liquid plasma treatment step of subjecting nanodiamonds that have undergone

The production method preferably includes an oxygen oxidation step of heating nanodiamonds in an oxygen-containing gas atmosphere after the oxidation treatment step and before the plasma treatment step in liquid.

In the submerged plasma treatment step, it is preferable to disperse nanodiamonds having a negative zeta potential.

It is preferable to carry out the above-mentioned in-liquid plasma treatment step under conditions where the pH exceeds 7.

The present invention also provides a nanodiamond dispersion composition containing a dispersion medium, nanodiamond particles dispersed in the dispersion medium, and tungsten.

According to the method for producing a nanodiamond dispersion composition of the present invention, a nanodiamond dispersion composition having excellent dispersibility of nanodiamond particles in a dispersion medium can be obtained while preventing the inflow of zirconia beads.

It is a process drawing which shows one Embodiment of the manufacturing method of the nanodiamond dispersion composition of this invention.

The method for producing the nanodiamond dispersion composition of the present invention includes a step of producing a nanodiamond crude product by a roaring method (production step) and graphite using an oxidizing agent from the nanodiamond crude product obtained in the above production step. (Oxidation treatment step) and a step of subjecting the nanodiamonds that have undergone the oxidation treatment step to plasma treatment in a liquid to disperse the nanodiamonds (in-liquid plasma treatment step). In addition, in this specification, the manufacturing method of the nanodiamond dispersion composition of this invention may be simply referred to as "the manufacturing method of this invention". The production method of the present invention may include other purification steps in addition to the production step, the oxidation treatment step, and the submerged plasma treatment step. Examples of the other purification steps include an acid treatment step, an alkaline superwater treatment step, an oxygen oxidation step, a hydrogenation treatment step, and a drying step.

FIG. 1 is a process diagram showing an embodiment of the manufacturing method of the present invention. One embodiment of the production method of the present invention shown in FIG. 1 includes at least a production step S1, an oxidation treatment step S2, an oxygen oxidation step S3, and a submerged plasma treatment step S4.

(Generation process)
In the production step (nanodiamond production step), a crude nanodiamond product is produced by a detonation method. Specifically, first, a molded explosive equipped with an electric detonator is installed inside a pressure-resistant container for detonation, and a gas having a specific composition and the explosive used coexist in the container. , Seal the container. The container is made of iron, for example. The volume of the container is, for example, 0.5 to 40 m ³ . As the explosive, a mixture of trinitrotoluene (TNT) and cyclotrimethylene trinitroamine or hexogen (RDX) can be used. The mass ratio of TNT to RDX (TNT / RDX) is, for example, in the range of 40/60 to 60/40. The amount of explosive used is, for example, 0.05 to 2.0 kg.

In the generation process, the electric detonator is then detonated and the explosive is detonated in the container. Detonation is an explosion that accompanies a chemical reaction in which the flame surface on which the reaction occurs moves at a high speed that exceeds the speed of sound. At the time of detonation, nanodiamonds are produced by the action of the pressure and energy of the shock wave generated by the explosion, using the carbon released by the explosive used as a partial incomplete combustion as a raw material. Nanodiamond is a product obtained by the detonation method. First of all, between adjacent primary particles or crystallites, in addition to the action of van der Waals force, the Coulomb interaction between crystal planes contributes to make nanodiamond very strong. It assembles and becomes an adhesive body.

In the production process, the container and its inside are then cooled by allowing it to cool at room temperature for about 24 hours. After this cooling, the nanodiamond crude products (including the nanodiamond adherents and soot produced as described above) adhering to the inner wall of the container are scraped off with a spatula. Collect the product. By the detonation method as described above, a crude product of nanodiamond particles can be obtained. In addition, it is possible to obtain a desired amount of crude nanodiamond product by performing the above-mentioned production steps a required number of times.

(Acid treatment process)
In the acid treatment step, a strong acid is allowed to act on the raw material nanodiamond crude product, for example, in an aqueous solvent to remove the metal oxide. The nanodiamond crude product obtained by the detonation method tends to contain metal oxides, and these metal oxides are oxides of Fe, Co, Ni, etc. derived from containers and the like used in the detonation method. .. For example, by allowing a strong acid to act in an aqueous solvent, metal oxides can be dissolved and removed from the crude nanodiamond product (acid treatment). The strong acid used for this acid treatment is preferably a mineral acid, and examples thereof include hydrochloric acid, hydrofluoric acid, sulfuric acid, nitric acid, and aqua regia. As the strong acid, one kind may be used, or two or more kinds may be used.

The concentration of the strong acid used in the acid treatment is, for example, 1 to 50% by mass. The acid treatment temperature is, for example, 70 to 150 ° C. The acid treatment time is, for example, 0.1 to 24 hours. Further, the acid treatment can be performed under reduced pressure, normal pressure, or pressure. After such acid treatment, the solid content (including the nanodiamond adherent) is washed with water, for example, by decantation. It is preferable to repeatedly wash the solid content with water by decantation until the pH of the precipitate reaches, for example, 2 to 3. When the content of the metal oxide in the crude nanodiamond product obtained by the detonation method is small, the above acid treatment may be omitted.

(Oxidation process)
The oxidation treatment step is a step of removing graphite from the crude nanodiamond product using an oxidizing agent. The crude nanodiamond product obtained by the detonation method contains graphite (graphite), which does not form nanodiamond crystals out of the carbon released by the explosive used due to partial incomplete combustion. Derived from graphite. For example, graphite can be removed from the crude nanodiamond product by allowing an oxidizing agent to act in an aqueous solvent after undergoing the above acid treatment. Further, by acting an oxidizing agent, an oxygen-containing group such as a carboxyl group or a hydroxyl group can be introduced into the surface of nanodiamond.

Examples of the oxidizing agent used in this oxidation treatment include chromic acid, chromic anhydride, dichromic acid, permanganic acid, perchloric acid, nitric acid, mixtures thereof, and at least one acid selected from these and others. Examples of mixed acids with acids (such as sulfuric acid) and salts thereof. Above all, it is preferable to use a mixed acid (particularly, a mixed acid of sulfuric acid and nitric acid) because it is environmentally friendly and has an excellent action of oxidizing and removing graphite.

The mixing ratio (former / latter; mass ratio) of sulfuric acid and nitric acid in the mixed acid is, for example, 60/40 to 95/5, even under pressure near normal pressure (for example, 0.5 to 2 atm). For example, it is preferable in that graphite can be efficiently oxidized and removed at a temperature of 130 ° C. or higher (particularly preferably 150 ° C. or higher; the upper limit is, for example, 200 ° C.). The lower limit is preferably 65/35, more preferably 70/30. The upper limit is preferably 90/10, more preferably 85/15, and even more preferably 80/20. When the mixing ratio is 60/40 or more, the content of sulfuric acid having a high boiling point is high, so that the reaction temperature becomes, for example, 120 ° C. or more under pressure near normal pressure, and the graphite removal efficiency tends to improve. is there. When the mixing ratio is 95/5 or less, the content of nitric acid that greatly contributes to the oxidation of graphite increases, so that the efficiency of removing graphite tends to improve.

The amount of the oxidizing agent (particularly the mixed acid) used is, for example, 10 to 50 parts by mass, preferably 15 to 40 parts by mass, and more preferably 20 to 40 parts by mass with respect to 1 part by mass of the crude nanodiamond product. The amount of sulfuric acid used in the mixed acid is, for example, 5 to 48 parts by mass, preferably 10 to 35 parts by mass, and more preferably 15 to 30 parts by mass with respect to 1 part by mass of the crude nanodiamond product. The amount of nitric acid used in the mixed acid is, for example, 2 to 20 parts by mass, preferably 4 to 10 parts by mass, and more preferably 5 to 8 parts by mass with respect to 1 part by mass of the crude nanodiamond product.

When the above mixed acid is used as the oxidizing agent, a catalyst may be used together with the mixed acid. By using a catalyst, the efficiency of removing graphite can be further improved. Examples of the catalyst include copper (II) carbonate and the like. The amount of the catalyst used is, for example, about 0.01 to 10 parts by mass with respect to 100 parts by mass of the crude nanodiamond product.

The oxidation treatment temperature is, for example, 100 to 200 ° C. The oxidation treatment time is, for example, 1 to 24 hours. The oxidation treatment can be performed under reduced pressure, normal pressure, or pressure.

If the metal oxide that could not be completely removed remains in the nanodiamond even after the above acid treatment step, the primary particles interact very strongly with each other to form an aggregate (secondary). It takes the form of particles). In such a case, the nanodiamond may be allowed to act with alkali and hydrogen peroxide in an aqueous solvent. As a result, the metal oxide remaining on the nanodiamond can be removed, and the separation of the primary particles from the adherent can be promoted.

After the above oxidation treatment step, it is preferable to remove the supernatant by, for example, decantation. Further, at the time of decantation, it is preferable to wash the solid content with water. Although the supernatant liquid at the beginning of washing with water is colored, it is preferable to repeatedly wash the solid content with water until the supernatant liquid becomes visually transparent.

(Drying process)
The production method of the present invention may include a drying step. For example, after evaporating the liquid content from the nanodiamond-containing solution obtained through the above oxidation treatment step using a spray drying device, an evaporator, or the like, the residual solid content generated thereby is heated and dried in a drying oven. dry. The heating and drying temperature is, for example, 40 to 150 ° C. By undergoing such a drying step, a nanodiamond adhering body (an adhering body of nanodiamond particles) can be obtained as a powder.

Further, the nanodiamond may be subjected to an oxidation treatment (for example, oxygen oxidation) or a reduction treatment (for example, hydrogenation treatment) in the gas phase, if necessary. By performing the oxidation treatment in the gas phase, nanodiamonds having many C = O groups on the surface can be obtained. Further, by performing the reduction treatment in the gas phase, nanodiamonds having many CH groups on the surface can be obtained. In particular, it is preferable to include an oxygen oxidation step from the viewpoint that it is easy to obtain a nanodiamond dispersion composition having excellent dispersibility of nanodiamonds through the submerged plasma treatment step.

(Oxygen oxidation process)
As the oxidation treatment, oxygen oxidation in which nanodiamond powder that has undergone the oxidation treatment step and, if necessary, another step such as a drying step is heated in a gas atmosphere containing oxygen using a gas atmosphere furnace. It is preferable to carry out the process. In the oxygen oxidation step, specifically, nanodiamond powder is arranged in a gas atmosphere furnace, oxygen-containing gas is supplied or passed through the furnace, and the inside of the furnace reaches a temperature condition set as a heating temperature. Is heated and oxygen oxidation treatment is carried out. The temperature condition of this oxygen oxidation treatment is, for example, 250 to 500 ° C. In order to realize a negative zeta potential for the nanodiamond particles contained in the produced nanodiamond dispersion, the temperature condition of this oxygen oxidation treatment is preferably relatively high, for example, 400 to 450 ° C. is there. Further, the oxygen-containing gas used in the oxygen oxidation step may be a mixed gas containing an inert gas in addition to oxygen. Examples of the inert gas include nitrogen, argon, carbon dioxide and helium. The oxygen concentration of the mixed gas is, for example, 1 to 35% by volume.

(Hydrogenation process)
In order to realize a positive zeta potential for the nanodiamonds contained in the produced nanodiamond dispersion composition, a hydrogenation step may be performed after the oxygen oxidation step. In the hydrogenation step, the nanodiamond powder that has undergone the oxygen oxidation step is heated in a gas atmosphere containing hydrogen using a gas atmosphere furnace. Specifically, hydrogen-containing gas is supplied or passed through a gas atmosphere furnace in which nanodiamond powder is arranged, and the temperature inside the furnace is raised to the temperature condition set as the heating temperature to generate hydrogen. Chemical processing is carried out. The temperature condition of this hydrogenation treatment is, for example, 400 to 800 ° C. Further, the hydrogen-containing gas used in the hydrogenation step may be a mixed gas containing an inert gas in addition to hydrogen. Examples of the inert gas include nitrogen, argon, carbon dioxide and helium. The hydrogen concentration of the mixed gas is, for example, 1 to 50% by volume.

(Submerged plasma treatment process)
In the submerged plasma treatment step, the nanodiamonds are subjected to plasma treatment in the liquid to disperse the nanodiamonds. The submerged plasma treatment can be performed using a known or conventional plasma generator. The submerged plasma treatment is performed using, for example, a reaction vessel in which a pair of electrodes for generating plasma are inserted so that the tips of the electrodes face each other and have a gap.

Examples of the liquid to be subjected to the plasma treatment in the liquid include water and an organic solvent. Examples of the organic solvent include those exemplified and described as the dispersion medium described later. Of these, water is preferable from the viewpoint of being able to generate plasma in the liquid more efficiently and disperse the nanodiamonds. As the above liquid, only one kind may be used, or two or more kinds may be used.

The concentration of nanodiamonds in the liquid in the plasma treatment step in the liquid is preferably 1 to 15% by mass, more preferably 2 to 8% by mass. When the concentration is 1% by mass or more (particularly 2% by mass or more), the reaction time is shortened. When the concentration is 15% by mass or less, the yield is improved.

The submerged plasma treatment is preferably performed under conditions where the pH exceeds 7. The pH is more preferably more than 7 and 14 or less, still more preferably 7.5 to 12, and particularly preferably 8 to 10. It is presumed that nanodiamonds (particularly nanodiamonds that have undergone oxygen oxidation treatment) are easily hydrophilized or oxidized by performing the submerged plasma treatment under conditions exceeding pH 7, and are susceptible to the effects of the submerged plasma treatment. The dispersibility in the obtained nanodiamond dispersion composition is more excellent. The pH may be adjusted so as to meet the above pH conditions. A known or commonly used pH adjuster such as sodium hydroxide can be used to adjust the pH.

Nanodiamonds subjected to submerged plasma treatment preferably have a negative zeta potential. In this case, it is presumed that the nanodiamonds are easily oxidized by the plasma treatment, and the dispersibility of the nanodiamonds is more excellent.

The submerged plasma treatment is a treatment involving heat generation, and is carried out at a temperature of, for example, 49 to 90 ° C., preferably 50 to 85 ° C., and a reaction time of, for example, about 1 minute to 3 hours, preferably about 10 minutes to 2 hours. Is preferable.

The distance between the electrodes that generate plasma (the distance between the tips of the pair of electrodes) is not particularly limited, but is, for example, 0.1 to 20 mm, preferably 0.2 to 15 mm, and more preferably 0.5 to 10 mm. Is. When the distance between the electrodes is within the above range, heat generation can be suppressed and plasma treatment can be sufficiently performed. Generally, when plasma-treating an electrolytic solution, hydrogen radicals are mainly generated when the distance between electrodes is short (for example, 2 mm or less), while hydroxyl radicals are generated when the distance between electrodes is long (for example, 5 mm or more). The distance between the electrodes is important, such as the occurrence of radicals becoming the mainstream. However, the manufacturing method of the present invention can surprisingly disperse nanodiamonds in a liquid over a wide range of interelectrode distance conditions.

After the above-mentioned in-liquid plasma treatment step, if necessary, after distilling off the liquid used for the in-liquid plasma with an evaporator or the like, a solvent may be newly mixed and stirred, that is, the solvent may be exchanged.

As described above, the nanodiamond dispersion composition in which nanodiamonds are dispersed in the dispersion medium can be obtained by the production method of the present invention.

According to the production method of the present invention, a nanodiamond dispersion composition having excellent dispersibility of nanodiamond can be obtained without crushing by bead mill treatment using zirconia beads. Further, according to the production method of the present invention, since the nanodiamond dispersion composition can be obtained by using a known plasma generator, the scale-up is easy and the productivity is excellent.

[Nanodiamond dispersion composition]
The nanodiamond dispersion composition of the present invention contains at least a dispersion medium, nanodiamonds dispersed in the dispersion medium, and tungsten. The nanodiamond dispersion composition of the present invention is a dispersion composition obtained by the production method of the present invention, and contains tungsten derived from an electrode.

In the nanodiamond dispersion composition of the present invention, nanodiamond particles are dispersed in a dispersion medium in nano size. The average dispersed particle diameter (D50, median diameter) of the nanodiamond particles in the nanodiamond dispersion composition of the present invention is preferably 1 to 100 nm, more preferably 2 to 80 nm, more preferably 5 to 50 nm, still more preferably 10. It is ~ 30 nm. The average dispersed particle size can be measured by a dynamic light scattering method. When the average dispersed particle size of the nanodiamond particles is within the above range, the dispersibility of the nanodiamond particles in the nanodiamond dispersion composition is excellent.

The content ratio of nanodiamond in the nanodiamond dispersion composition of the present invention is, for example, 0.1% by mass or more and 5.0% by mass or less, preferably 0.2% by mass or more and 4.0% by mass or less, more preferably 0. It is 5.5 mass ppm or more and 3.0 mass% or less, more preferably 1 mass ppm or more and 2.0 mass% or less, and may be 1 to 100 mass ppm. The nanodiamond dispersion composition of the present invention is more excellent in dispersibility in the dispersion medium at a content ratio in the above range.

The dispersion medium is a medium for dispersing nanodiamonds, and examples thereof include water, organic solvents, and ionic liquids. As the dispersion medium, only one kind may be used, or two or more kinds may be used.

The organic solvent includes, for example, a protic organic solvent and an aprotic organic solvent, and includes a polar organic solvent and a non-polar organic solvent.

The organic solvent has an SP value [(cal / cm ³ ) ^0.5 : Fedors calculated value] at 25 ° C., for example, 7 to 23, preferably 7 to 17, more preferably 7 to 15, and even more preferably 7 to. 13, more preferably 7 to 12, particularly preferably 7 to 10.

Further, the above-mentioned organic solvent has a relative permittivity at 25 ° C., for example, 1 to 40, preferably 2 to 3. The relative permittivity in this specification is a value described in the Chemical Handbook, 5th Edition, Basic Edition, Maruzen Co., Ltd., and the Chemical Society of Japan. For the relative permittivity, an organic solvent was injected into a glass cell with an ITO transparent electrode having a cell gap of 10 μm, and the electric capacity of the obtained cell was measured using a model 2353LCR meter (measurement frequency: 1 kHz) manufactured by NF Co., Ltd. It can also be obtained by measuring at 25 ° C. and 40% RH.

The polar organic solvent has an SP value at 25 ° C. of, for example, 10.0 or more, preferably 10.0 to 23.0, and more preferably 10.0 to 15.0. The non-polar organic solvent has an SP value at 25 ° C. of, for example, less than 10.0, preferably 7.5 to 9.5, and more preferably 8.0 to 9.3. The polar organic solvent has a relative permittivity at 25 ° C., for example, 15 to 40, preferably 15 to 35, and more preferably 18 to 35. The non-polar organic solvent has a relative permittivity at 25 ° C. of, for example, 1 or more, preferably less than 15, more preferably 1 to 10, and even more preferably 1 to 5.

Examples of the protic organic solvent include methanol (SP value: 13.8, relative permittivity: 32.6), ethanol (SP value: 12.6, relative permittivity: 24.30), and 1-propanol (SP). Value: 11.8, relative permittivity: 20.1), monovalent alcohol having 1 to 5 carbon atoms such as isopropyl alcohol (SP value: 11.6, relative permittivity: 19.92); carbon such as ethylene glycol Examples thereof include polyhydric alcohols of numbers 2 to 5.

Examples of the aproton organic solvent include toluene (SP value: 9.14, relative permittivity: 2.379), o-xylene (SP value: 9.10), aromatic hydrocarbons such as benzene; cyclohexane and the like. Alicyclic hydrocarbons; aliphatic hydrocarbons such as n-hexane (SP value: 7.29); halogenated hydrocarbons such as carbon tetrachloride, methylene chloride, ethylene dichloride, chloroform; isopropyl ether, tetrahydrofuran (SP). Values such as ethers such as diethyl ether (SP value: 7.25); ethyl acetate (SP value: 8.75), esters such as butyl acetate (SP value: 8.70); acetone (SP value) : 9.07, relative permittivity: 20.7), methyl ethyl ketone (SP value: 8.99), cyclohexanone (SP value: 9.80) and other ketones.

The nanodiamond dispersion composition of the present invention contains at least tungsten. The content ratio of tungsten in the nanodiamond dispersion composition of the present invention is, for example, 10 to 2000 mass ppm, preferably 15 to 1750 mass ppm, more preferably 20 to 1500 mass ppm, still more preferably 25 to 1250 mass ppm. ..

The content ratio of zirconia in the nanodiamond dispersion composition of the present invention is, for example, 60 mass ppm or less, preferably 40 mass ppm or less, and more preferably 20 mass ppm or less. According to the production method of the present invention, nanodiamonds can be dispersed without going through a crushing step using a bead mill such as zirconia, so that mixing of zirconia from the bead mill can be avoided, and the above-mentioned zirconia concentration can be avoided. Nanodiamond dispersion composition can be obtained.

The content ratio of tungsten and zirconia shall be determined based on the amount of W or Si detected based on the dispersion liquid whose content ratio is known by detecting W by high frequency inductively coupled plasma emission spectroscopy (ICP emission spectroscopy). Can be done.

The nanodiamond dispersion composition of the present invention preferably has a haze value of 5 or less, more preferably 3 or less, and even more preferably 1 or less. Since the nanodiamond dispersion composition of the present invention is excellent in dispersibility of nanodiamond particles, the nanodiamond dispersion composition having the above haze value can be obtained. The haze value can be measured based on JIS K 7136.

The nanodiamond dispersion composition of the present invention may consist only of a dispersion medium, nanodiamond, and tungsten, or may contain other components. Other components include, for example, surfactants, thickeners, coupling agents, dispersants, rust preventives, corrosion inhibitors, freezing point lowering agents, defoamers, abrasion resistant additives, preservatives, colorants and the like. Can be mentioned. As the other components, only one kind may be used, or two or more kinds may be used.

The nanodiamond dispersion composition of the present invention can be preferably used, for example, as an additive that imparts the characteristics of fine nanodiamond particles to a resin or the like (for example, a heat or photocurable resin, a thermoplastic resin, or the like). .. Examples of the characteristics of the nanodiamond particles include mechanical strength, high refractive index, thermal conductivity, insulating property, antioxidant property, crystallization promoting action, and dendrite suppressing action. The composition obtained by adding the nanodiamond dispersion composition of the present invention to a resin is, for example, a functional hybrid material, a thermal function (heat resistance, heat storage, thermoconductivity, heat insulation, etc.) material, and photonics (organic EL element). , LED, liquid crystal display, optical disk, etc.) material, bio / biocompatible material, coating material, film (hard coat film for touch panel and various displays, heat shield film, etc.) material, sheet material, screen (transmissive transparent screen, etc.) ) Materials, fillers (fillers for heat dissipation, fillers for improving mechanical properties, etc.), heat-resistant plastic substrates (substrates for flexible displays, etc.), lithium-ion batteries, etc. can be preferably used. In addition, the nanodiamond dispersion composition of the present invention is preferably used as an anti-friction agent or a lubricant (initial familiar use, present lubrication use, etc.) applied to sliding parts of mechanical parts (for example, automobiles, aircraft, etc.). Can be used.

Hereinafter, the present invention will be described in more detail based on Examples, but the present invention is not limited to these Examples.

Example 1
The nanodiamond dispersion composition was produced through the following steps.

(Generation process)
First, the process of producing nanodiamonds by the detonation method was performed. In this step, first, a molded explosive equipped with an electric detonator was installed inside a pressure-resistant container for detonation, and the container was sealed. The container is made of iron and the volume of the container is 15 m ³ . As the explosive, 0.50 kg of a mixture of TNT and RDX was used. The mass ratio of TNT to RDX (TNT / RDX) in this explosive is 50/50. Next, the electric detonator was detonated and the explosive was detonated in the container (generation of nanodiamonds by the detonation method). Next, the temperature of the container and its inside was lowered by leaving it at room temperature for 24 hours. After this cooling, the crude nanodiamond products adhering to the inner wall of the container (including the adherents of nanodiamond particles and soot generated by the above detonation method) are scraped off with a spatula, and the nanodiamonds are removed. The crude product was recovered.

(Acid treatment process)
Next, an acid treatment step was carried out on the nanodiamond crude product obtained by carrying out the above-mentioned formation step a plurality of times. Specifically, the slurry obtained by adding 6 L of 10% by mass hydrochloric acid to 200 g of the crude nanodiamond product was heat-treated for 1 hour under reflux under normal pressure conditions. The heating temperature in this acid treatment is 85 to 100 ° C. Next, after cooling, the solid content (including nanodiamond adherents and soot) was washed with water by decantation. The solid content was repeatedly washed with water by decantation until the pH of the precipitate was from the low pH side to 2.

(Oxidation process)
Next, an oxidation treatment step was performed. Specifically, 6 L of 98% by mass sulfuric acid and 1 L of 69% by mass nitric acid were added to a precipitate (including nanodiamond adherents) obtained through decantation after acid treatment to form a slurry, which was then added to form a slurry. This slurry was heat-treated for 48 hours under reflux under normal pressure conditions. The heating temperature in this oxidation treatment is 140 to 160 ° C. Next, after cooling, the solid content (including the nanodiamond adherent) was washed with water by decantation. The supernatant liquid at the beginning of washing with water was colored, and the solid content was washed with water repeatedly by decantation until the supernatant liquid became visually transparent.

(Drying process)
Next, 1000 mL of the nanodiamond-containing liquid obtained through the above-mentioned washing treatment was spray-dried (drying) using a spray-drying device (trade name "Spray Dryer B-290", manufactured by Nippon Buch Co., Ltd.). Process). As a result, 50 g of nanodiamond powder was obtained.

(Oxygen oxidation process)
Next, 4.5 g of the nanodiamond powder obtained as described above was allowed to stand in the core tube of a gas atmosphere furnace (trade name "gas atmosphere tube furnace KTF045N1", manufactured by Koyo Thermo System Co., Ltd.), and the core tube was placed. After continuing to pass nitrogen gas at a flow rate of 1 L / min for 30 minutes, the flowing gas is switched from nitrogen to a mixed gas of oxygen and nitrogen, and the mixed gas is passed through the core tube at a flow rate of 1 L / min. Continued. The oxygen concentration in the mixed gas is 4% by volume. After switching to the mixed gas, the temperature inside the furnace was raised to 400 ° C., which is the set heating temperature. The rate of temperature rise was 10 ° C./min up to 380 ° C., which is 20 ° C. lower than the set heating temperature, and 1 ° C./min from 380 ° C. to 400 ° C. thereafter. Then, while maintaining the temperature condition in the furnace at 400 ° C., the nanodiamond powder in the furnace was subjected to oxygen oxidation treatment (oxygen oxidation step). The processing time was 3 hours.

The zeta potential of the nanodiamond powder obtained as described above was measured by a laser Doppler electrophoresis method using an apparatus manufactured by Malvern (trade name "Zetasizer Nano ZS"). The nanodiamond dispersion liquid subjected to the measurement was diluted with ultrapure water so that the nanodiamond concentration was 0.2% by mass, and then subjected to ultrasonic irradiation with an ultrasonic cleaner. The zeta potential measurement temperature is 25 ° C. As a result of this measurement, the zeta potential of the nanodiamond dispersion was -38 mV.

(Submerged plasma treatment process)
Next, 6 g of nanodiamond was mixed with 114 g of water so that the concentration of nanodiamond was 5% by mass to prepare a slurry, and an aqueous sodium hydroxide solution was added to adjust the pH to 9.9. A plasma generating electrode was inserted into a reaction vessel so that the distance between the electrodes was 5 mm, a pH-adjusted slurry was transferred thereto, and a submerged plasma reaction was carried out at room temperature for 1 hour while stirring the slurry with a rotor. .. The product name "MPP04-A4-200" (manufactured by Kurita Seisakusho Co., Ltd.) was used as the plasma generator.

After allowing the slurry liquid after the reaction to stand, the supernatant liquid was collected and subjected to a centrifugal separation treatment (centrifugal force 13000 × g, centrifugation time 15 minutes) to recover the sedimented solid content. 2 g of IPA (SP: 11.5) is added to the solid content recovered in this manner, and ultrasonic treatment is performed for 10 minutes using an ultrasonic treatment device (trade name "ASU-10", manufactured by AS ONE Corporation). To obtain a nanodiamond dispersion composition.

The particle size distribution of the nanodiamond particles in the obtained nanodiamond dispersion composition is subjected to a dynamic light scattering method (non-contact backscattering method) using an apparatus manufactured by Malvern (trade name "Zetasizer Nano ZS"). The average dispersed particle size (D50) of the nanodiamond particles was determined by 13.7 nm. At this time, the nanodiamond concentration was 0.28% by mass, and it was confirmed that tungsten was contained in a proportion of 50% by mass or less. The nanodiamond concentration was calculated from the absorbance at 350 nm. The tungsten concentration was determined by ICP emission spectroscopy.

Example 2
In the submerged plasma treatment step, a nanodiamond dispersion composition was produced in the same manner as in Example 1 except that the distance between the electrodes was 1 mm. When the average dispersed particle size (D50) of the nanodiamond particles was determined, it was 15.2 nm. At this time, the nanodiamond concentration was 0.21% by mass, and the tungsten concentration was 1000% by mass.

Example 3
The production step, the acid treatment step, the oxidation treatment step, the drying step, and the oxygen oxidation step were carried out in the same manner as in Example 1, and then the hydrogenation step was carried out using the gas atmosphere furnace in the oxygen oxidation step. Specifically, nitrogen gas is continuously passed through a gas atmosphere furnace in which nanodiamond powder that has undergone an oxygen oxidation step is arranged at a flow rate of 1 L / min for 30 minutes, and then the flowing gas is transferred from nitrogen. The gas was switched to a mixed gas of hydrogen and nitrogen, and the mixed gas was continuously passed through the core tube at a flow rate of 1 L / min. The hydrogen concentration in the mixed gas is 2% by volume. After switching to the mixed gas, the temperature inside the furnace was raised to the set heating temperature of 600 ° C. The heating rate was 10 ° C./min. Then, while maintaining the temperature condition in the furnace at 600 ° C., the nanodiamond powder in the furnace was subjected to hydrogen oxidation treatment. The processing time was 5 hours. Using the nanodiamond powder that had undergone the hydrogenation step, a submerged plasma treatment step was carried out in the same manner as in Example 1 to produce a nanodiamond dispersion composition. The average dispersed particle size (D50) of the nanodiamond particles was determined and found to be 23.3 nm. At this time, the nanodiamond concentration was 0.006 mass%, and it was confirmed that tungsten was contained in a proportion of 50 mass ppm or less.

Example 4
In the submerged plasma treatment step, a nanodiamond dispersion composition was produced in the same manner as in Example 3 except that the distance between the electrodes was 1 mm. The average dispersed particle size (D50) of the nanodiamond particles was determined and found to be 22.3 nm. At this time, the nanodiamond concentration was 0.007 mass% and the tungsten concentration was 800 mass ppm.

Example 5
Using the nanodiamond powder obtained in the drying step, a nanodiamond dispersion composition was produced in the same manner as in Example 1 except that it was subjected to a submerged plasma treatment step without going through an oxygen oxidation step. When the average dispersed particle size (D50) of the nanodiamond particles was determined, it was about 79 nm. At this time, the nanodiamond concentration was 0.081 mass%, and it was confirmed that tungsten was contained in a proportion of 50 mass ppm or less.

Example 6
In the submerged plasma treatment step, a nanodiamond dispersion composition was produced in the same manner as in Example 5 except that the distance between the electrodes was 1 mm. When the average dispersed particle size (D50) of the nanodiamond particles was determined, it was about 52 nm. At this time, the nanodiamond concentration was 0.063% by mass, and the tungsten concentration was 850% by mass.

As a summary of the above, the configuration of the present invention and variations thereof are described below.
[Appendix 1] A production step of obtaining a crude nanodiamond product by a roaring method, an oxidation treatment step of removing graphite from the crude nanodiamond product obtained in the production step using an oxidizing agent, and the oxidation treatment step were performed. A method for producing a nanodiamond dispersion composition, which comprises an in-liquid plasma treatment step of subjecting nanodiamonds to plasma treatment in a liquid to disperse the nanodiamonds.
[Appendix 2] After the production step and before the submerged plasma step (preferably before the oxidation treatment step), the crude nanodiamond product obtained in the production step contains a strong acid (preferably containing a mineral acid). A strong acid, more preferably a strong acid containing one or more acids selected from the group consisting of hydrochloric acid, hydrofluoric acid, sulfuric acid, nitric acid, and aqua regia) is allowed to act to remove the metal oxide. , The method for producing a nanodiamond dispersion composition according to Appendix 1.
[Appendix 3] The method for producing a nanodiamond dispersion composition according to Appendix 1 or 2, wherein the oxidizing agent contains a mixed acid of two kinds of acids (preferably a mixed acid of sulfuric acid and nitric acid).
[Appendix 4] The mixing ratio (former / latter; mass ratio) of sulfuric acid and nitric acid in the mixed acid is 60/40 to 95/5 (preferably 65/35 to 90/10, more preferably 70/30 to 85). The method for producing a nanodiamond dispersion composition according to Appendix 3, which is / 15, more preferably 70/30 to 80/20).
[Appendix 5] After the acid treatment step and before the liquid plasma treatment step, the nanodiamond crude product obtained through the acid treatment step is subjected to alkali and hydrogen peroxide in an aqueous solution to cause a metal. The method for producing a nanodiamond dispersion composition according to any one of Supplementary note 1 to 4, which comprises a step of removing an oxide.
[Appendix 6] After the oxidation treatment step, the supernatant is removed and the solid content is washed with water, and the solid content is repeatedly washed with water until the supernatant is visually transparent. The method for producing a nanodiamond dispersion composition according to any one.
[Supplementary Note 7] The nanodiamond dispersion composition according to any one of Supplementary notes 1 to 6, which comprises a drying step of drying the nanodiamond-containing solution obtained through the oxidation treatment step to obtain a nanodiamond adherent. Manufacturing method.
[Appendix 8] The method for producing a nanodiamond dispersion composition according to Appendix 7, which comprises an oxygen oxidation step of heating the nanodiamond adhering body obtained after the drying step in an oxygen-containing gas atmosphere.
[Appendix 9] Any one of Appendix 1 to 8, which comprises an oxygen oxidation step of heating nanodiamonds in an oxygen-containing gas atmosphere after the oxidation treatment step and before the submerged plasma treatment step. The method for producing a nanodiamond dispersion composition according to 1.
[Appendix 10] The method for producing a nanodiamond dispersion composition according to any one of Supplementary notes 1 to 9, wherein nanodiamonds having a negative zeta potential are dispersed in the submerged plasma treatment step.
[Supplementary Note 11] The method for producing a nanodiamond dispersion composition according to any one of Supplementary notes 1 to 10, wherein the in-liquid plasma treatment step is performed under a condition where the pH exceeds 7.
[Supplementary Note 12] The method for producing a nanodiamond dispersion composition according to any one of Supplementary notes 1 to 11, wherein the in-liquid plasma treatment step is performed in water.
[Appendix 13] The method for producing a nanodiamond dispersion composition according to any one of Supplementary notes 1 to 12, wherein the in-liquid plasma treatment step is performed at 49 to 90 ° C. (preferably 50 to 85 ° C.).
[Appendix 14] The submerged plasma treatment step is performed under the condition that the distance between the electrodes that generate plasma is 0.1 to 20 mm (preferably 0.2 to 15 mm, more preferably 0.5 to 10 mm). The method for producing a nanodiamond dispersion composition according to any one of 13.

[Appendix 15] A nanodiamond dispersion composition containing a dispersion medium, nanodiamond particles dispersed in the dispersion medium, and tungsten.
[Appendix 16] The method for producing a nanodiamond dispersion composition according to Appendix 15, wherein the nanodiamond particles are dispersed in the dispersion medium in a nano size.
[Appendix 17] The average dispersed particle diameter (D50, median diameter) of the nanodiamond particles in the nanodiamond dispersion composition is 1 to 100 nm (preferably 2 to 80 nm, more preferably 5 to 50 nm, still more preferably 10 to 10 to 30 nm). The method for producing a nanodiamond dispersion composition according to Appendix 15 or 16.
[Supplementary Note 18] The method for producing a nanodiamond dispersion composition according to any one of Supplementary notes 15 to 17, wherein the dispersion medium contains an organic solvent.
[Appendix 19] The organic solvent has an SP value [(cal / cm ³ ) ^0.5 : Fedors calculated value] at 25 ° C. of 7 to 23 (preferably 7 to 17, more preferably 7 to 15, still more preferably 7 to 7 to]. 13. The method for producing a nanodiamond dispersion composition according to Appendix 18, further preferably 7 to 12, particularly preferably 7 to 10).
[Supplementary Note 20] The method for producing a nanodiamond dispersion composition according to Supplementary note 18 or 19, wherein the organic solvent has a relative permittivity of 1 to 40 (preferably 2 to 3) at 25 ° C.
[Appendix 21] The content ratio of the tungsten in the nanodiamond dispersion composition is 10 to 2000 mass ppm (preferably 15 to 1750 mass ppm, more preferably 20 to 1500 mass ppm, still more preferably 25 to 1250 mass ppm. ). The method for producing a nanodiamond dispersion composition according to any one of Appendix 15 to 20.
[Appendix 22] The content of zirconia in the nanodiamond dispersion composition is 60 mass ppm or less (preferably 40 mass ppm or less, more preferably 20 mass ppm or less) according to any one of Appendix 15 to 21. Method for producing nanodiamond dispersion composition.
[Appendix 23] The method for producing a nanodiamond dispersion composition according to any one of Appendix 15 to 22, wherein the haze value is 5 or less (preferably 3 or less, more preferably 1 or less).

S1 generation step S2 oxidation treatment step S3 oxygen oxidation step S4 liquid plasma treatment step

Claims (5)

1. A production step of obtaining a nanodiamond crude product by the detonation method, an oxidation treatment step of removing graphite from the nanodiamond crude product obtained in the production step using an oxidizing agent, and a liquid nanodiamond that has undergone the oxidation treatment step. A method for producing a nanodiamond dispersion composition, which comprises a submerged plasma treatment step of dispersing nanodiamonds by subjecting them to plasma treatment.
2. The production of the nanodiamond dispersion composition according to claim 1, which comprises an oxygen oxidation step of heating the nanodiamonds in an oxygen-containing gas atmosphere after the oxidation treatment step and before the liquid plasma treatment step. Method.
3. The method for producing a nanodiamond dispersion composition according to claim 1 or 2, wherein in the submerged plasma treatment step, nanodiamonds having a negative zeta potential are dispersed.
4. The method for producing a nanodiamond dispersion composition according to any one of claims 1 to 3, wherein the in-liquid plasma treatment step is performed under a condition where the pH exceeds 7.
5. A nanodiamond dispersion composition containing a dispersion medium, nanodiamond particles dispersed in the dispersion medium, and tungsten.

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