JP7551446B2 - Composition and heat transport device - Google Patents

Description

The present invention relates to a composition and a heat transport device.

Conventionally, heat transport devices such as heat pipes have been used to cool electronic devices. In general, a heat pipe is a heat transport device that transports heat by utilizing the phase change of a medium that occurs when part of a pipe containing the medium is heated. However, as electronic devices become smaller, the heat generation density (the value obtained by dividing the amount of heat generated by the surface area) increases, and even when conventional heat transport devices are used, the processing speed of the electronic devices decreases and breakdowns due to heat generation occur. For this reason, there is a demand for a heat transport device that is small to match the size of electronic devices and has a large amount of heat transport (high efficiency).

Patent Document 1 describes a magnetic fluid drive device that includes a circulation flow path in which a magnetic fluid is sealed, a heating section in the circulation flow path, and a magnetic field application section that applies a magnetic field to the magnetic fluid in the heating section. Specifically, the device uses a magnetic fluid that contains ferrite particles, which are magnetic fine particles that have the property of decreasing magnetization as the temperature increases, and kerosene and hexane, which are oil-based media, and uses the difference in magnetization between the heated and non-heated sections in the circulation flow path to drive the magnetic fluid.

Patent Document 2 describes a magnetic fluid in which the surfaces of ferrite particles are coated with oleic acid and sodium dodecylbenzenesulfonate, a surfactant, and then dispersed in water. Furthermore, Patent Document 3 describes a temperature-sensitive magnetic fluid that contains ferrite particles with 3-mercaptopropionic acid attached to the surface and an aqueous dispersion medium.

JP 2014-134335 A Special Publication No. 7-38328 JP 2018-41807 A

As a result of the inventors' investigations, it was found that even if the magnetic fluids described in Patent Documents 2 and 3 are applied to the magnetic fluid drive device described in Patent Document 1, the storage stability of the magnetic fluid cannot be obtained due to a decrease in the dispersibility of the ferrite particles contained in the magnetic fluid, and the amount of heat transport is reduced.

Therefore, an object of the present invention is to provide a composition that has high dispersibility of magnetic particles and provides storage stability. Another object of the present invention is to provide a heat transport device that uses the composition.

The present invention relates to a composition comprising particles, a dispersant, and an aqueous medium containing water,
The particles include magnetic particles represented by the following formula (1):
The dispersant comprises polyacrylic acid or a salt thereof;
A composition characterized in that the weight average molecular weight of the dispersant is 4,500 or more and 7,000 or less .
(MnO) _x ・(ZnO) _y ・(Fe ₂ O ₃ ) _z ...Formula (1)
Here, x, y, and z satisfy 0.15≦x≦0.40, 0.10≦y≦0.25, 0.48≦z≦0.60, and x+y+z=1.

The present invention provides a composition that has high dispersibility of magnetic particles and provides storage stability, and a heat transport device that uses the composition.

FIG. 1 is a diagram illustrating the principle of heat transport by the composition of the present invention. 1 is a schematic diagram showing an example of a heat transport device of the present invention. 3 is a schematic diagram showing in detail a magnetic field application unit of the heat transport device of FIG. 2. 3 is a diagram showing an example of a transport device incorporating the heat transport device of FIG. 2; FIG. 13 is a diagram showing an example of a parallel arrangement of heat transfer devices according to the present invention.

The following describes in detail the embodiments of the present invention. Unless otherwise specified, the various physical properties are values at a temperature of 25°C.

The composition of the present invention contains particles including magnetic particles and an aqueous medium. When heat transport is performed using a composition containing magnetic particles, the flow rate of the composition needs to be increased in order to increase the amount of heat transport. Here, in order to increase the flow rate of the composition, it is important to reduce the viscosity of the composition and the flow resistance of the composition. Compared to the oil-based medium used in the magnetic fluid described in Patent Document 1, the viscosity of the aqueous medium is low. Therefore, by using an aqueous medium as a medium for dispersing magnetic particles, the viscosity of the composition itself can be reduced. In addition, in order to increase the amount of heat transport, it is necessary to use a medium with a large heat capacity or thermal conductivity. In general, compared to oil-based media, aqueous media have a large heat capacity and thermal conductivity. Therefore, by using an aqueous medium as a medium for dispersing magnetic particles, it is possible to increase the amount of heat transport of the composition.

Furthermore, in addition to the magnetic particles, the particles contain a dispersant containing polyacrylic acid or a salt thereof, and the magnetic particles are dispersed in the dispersant containing polyacrylic acid or a salt thereof. By using polyacrylic acid or a salt thereof as a dispersant, the magnetic particles can be stably dispersed due to electrostatic repulsion caused by the carboxyl groups contained therein and steric hindrance caused by the use of the resin, and the storage stability of the composition is improved.

When using the magnetic fluid described in Patent Document 2, sodium dodecylbenzenesulfonate, which contributes to the dispersion of magnetic particles, adheres to the magnetic particles by physical adsorption via oleic acid and is easily detached. This reduces the dispersibility of the magnetic particles, and the magnetic fluid cannot be stored with stability. In addition, 3-mercaptopropionic acid, which is used in Patent Document 3 as a dispersant for magnetic particles, has a short molecular chain and is therefore less compatible with water. This reduces the dispersibility of the magnetic particles, and the magnetic fluid cannot be stored with stability.

Each ingredient is described in detail below.

[Composition]
The composition of the present invention contains particles and an aqueous medium containing water, and the particles contain magnetic particles and a dispersant containing polyacrylic acid or a salt thereof.

<Magnetic particles>
The magnetic particles may be particles that exhibit superparamagnetism, which is a property exhibited in nanometer-sized particles of ferromagnetic materials that exhibit a property that magnetization decreases when the temperature exceeds the Curie temperature specific to the magnetic material, that is, that magnetization decreases with increasing temperature.

When a magnetic field is applied to particles that exhibit superparamagnetism, the magnetization of the particles aligns in the direction of the magnetic field; when a magnetic field is not applied, the magnetization is not fixed within the particles due to thermal energy, but rotates randomly, resulting in zero magnetization of the particles as a whole. Therefore, by using a composition containing particles that exhibit superparamagnetism as magnetic particles, when a magnet is brought close to the composition, i.e., when a magnetic field is applied to the composition, the magnetized particles are attracted to the magnet. On the other hand, when a magnet is moved away from the composition, i.e., when a magnetic field is not applied to the composition, it becomes difficult for magnetization to occur in the particles, and the particles become difficult to attract to the magnet. In this way, a composition containing particles that exhibit superparamagnetism can be controlled by magnetic force.

Examples of particles exhibiting superparamagnetism include ferrite particles. Here, ferrite refers to a salt of a divalent metal of the type M ^II O.Fe ₂ O _3. Examples of M ^II include Mn, Fe, Co, Ni, Cu, Zn, Mg, Cd, and Ca. As ferrite particles, it is preferable to use magnetite (FeO.Fe ₂ O ₃ ) particles, manganese zinc ferrite ((MnO) _x .(ZnO) _{1-x.Fe 2} O ₃ ) particles, and manganese calcium zinc ferrite ((MnO) _x .(CaO) _y .(ZnO) _{z.Fe 2} O ₃ ) particles. Here, x + y + z = 1.

Among them, it is preferable to use manganese zinc ferrite as the ferrite particles from the viewpoint of high magnetization. In particular, manganese zinc ferrite particles represented by the following formula (1) show a large decrease in magnetization with increasing temperature in the temperature range of 0°C to 100°C, and exhibit strong temperature dependency (thermosensitivity). This provides a high driving force for transporting heat, allowing efficient heat transport.
(MnO) _x・(ZnO) _y・(Fe ₂ O ₃ ) _z ...Formula (1)
In the formula (1), x, y, and z satisfy 0.15≦x≦0.40, 0.10≦y≦0.25, 0.48≦z≦0.60, and x+y+z=1.

The above formula (1) may further contain at least one compound selected from the group consisting of SrO, NiO, MgO, and CaO in a ratio of 0.01 to 0.10. The addition of these compounds improves magnetization, provides a driving force for transporting heat, and allows for more efficient heat transport. In addition, the magnetic particles preferably contain at least two or more elements selected from the group consisting of Zn, Mn, Fe, Ni, Sr, Mg, and Ca. In addition, the magnetic particles preferably contain at least two or more elements selected from the group consisting of Zn, Mn, and Fe.

The content of the magnetic particles is preferably 20.0 parts by mass or more and 50.0 parts by mass or less, and more preferably 30.0 parts by mass or more and 50.0 parts by mass or less, based on the total mass of the composition.

<Dispersant>
The dispersant for dispersing the magnetic particles includes polyacrylic acid or a salt thereof. The dispersant adheres to the magnetic particles to coat the particle surface, making it possible to stably disperse the magnetic particles in an aqueous medium. Here, the dispersant coating the particle surface does not necessarily mean that the dispersant covers the entire particle, but may only cover a portion of the particle, and the layer of the coating dispersant need not be uniform.

Examples of salts of polyacrylic acid include alkali metal salts, ammonium salts, and organic ammonium salts of polyacrylic acid. Examples of alkali metals include lithium, sodium, and potassium. Examples of organic ammonium include alkylamines having 1 to 3 carbon atoms, such as methylamine and ethylamine. Of these, it is preferable that the polyacrylic acid is an alkali metal salt type, such as sodium or potassium, or an organic ammonium salt type.

The amount of polyacrylic acid or its salt used is preferably 5 parts by weight or more and 100 parts by weight or less, and more preferably 10 parts by weight or more and 50 parts by weight or less, per 100 parts by weight of magnetic particles. If the amount of dispersant is too small relative to the magnetic particles, it becomes difficult to stably disperse the magnetic particles, and sufficient storage stability may not be obtained. Furthermore, if the amount of dispersant is too large relative to the magnetic particles, the viscosity of the composition increases, and the flow resistance of the composition increases. This may result in a decrease in the flow rate of the composition, and a decrease in the heat transport amount of the composition.

The weight average molecular weight of polyacrylic acid or its salt is preferably 3000 or more and 20000 or less. If the weight average molecular weight is less than 3000, it becomes difficult to stably disperse the magnetic particles, and sufficient storage stability may not be obtained. If the weight average molecular weight exceeds 20000, the viscosity of the composition increases, and the flow resistance of the composition increases. This may result in a decrease in the flow rate of the composition, and a decrease in the amount of heat transport of the composition. Furthermore, the weight average molecular weight of polyacrylic acid or its salt is preferably 4500 or more and 7000 or less. Here, the weight average molecular weight is the weight average molecular weight calculated in terms of polystyrene by gel permeation chromatography.

The content of the dispersant is preferably 1.0 part by mass or more and 20.0 parts by mass or less, and more preferably 1.0 part by mass or more and 8.0 parts by mass or less, based on the total mass of the composition.

[Cumulative 50% particle diameter (D ₅₀ ) based on volume of particles]
The particle volume-based cumulative 50% particle size ( _D50 ) is preferably 200 nm or less. Here, according to Stokes' equation, the settling speed of the particles increases in proportion to the square of the particle size. Therefore, if _D50 exceeds 200 nm, the settling speed of the particles increases, and the dispersibility of the particles decreases, so that the storage stability of the composition may not be sufficient. Also, _D50 is preferably 10 nm or more. If _D50 is less than 10 nm, the specific surface area of the magnetic particles increases, and they are easily oxidized in an aqueous medium.

[Cumulative 90% particle diameter (D ₉₀ ) based on volume of particles]
The particles preferably have a volume-based cumulative 90% particle size (D ₉₀ ) of 500 nm or less. If D ₉₀ exceeds 500 nm, the dispersibility of the magnetic particles decreases, and the storage stability of the composition may not be sufficient.

_D50 and _D90 refer to the dispersed particle diameter of magnetic particles dispersed in a dispersant, and can be measured by a dynamic light scattering method (DLS method).

<Aqueous medium>
The aqueous medium contains water. The aqueous medium preferably further contains a water-soluble organic solvent. From the viewpoint of the viscosity of the composition, the content of the water-soluble organic solvent is preferably 10 parts by mass or more and 100 parts by mass or less with respect to 100 parts by mass of water. Examples of the water-soluble organic solvent include polyhydric alcohols such as glycol. More specifically, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, and glycerin are included. The content of the aqueous medium is preferably 30.0 parts by mass or more and 80.0 parts by mass or less based on the total mass of the composition. If the content of water is less than 30 parts by mass, the viscosity of the composition increases, so the flow rate of the composition decreases, and as a result, the amount of heat transport may also decrease. If the content of water in the composition exceeds 80 parts by mass, the amount of magnetic particles contained in the composition decreases, so that the driving force for transporting heat may not be obtained sufficiently.

<Other ingredients>
The composition of the present invention may contain other components in addition to the above-mentioned components, if necessary, such as various additives including a pH adjuster, a surfactant, an anti-rust agent, a preservative, an anti-fungal agent, an antioxidant, an anti-reducing agent, an evaporation promoter, and a chelating agent.

The pH adjuster adjusts the pH of the composition. The pH of the composition is preferably 7 or more and 14 or less, more preferably 8 or more and 13 or less, and even more preferably 8 or more and 12 or less. When the composition has a pH in the above range, the carboxyl groups of the polyacrylic acid or its salt, which is the dispersant for the magnetic particles, are ionized and become more compatible with water, allowing the magnetic particles to be stably dispersed in an aqueous medium. Examples of pH adjusters include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, and calcium hydroxide, alkaline earth metal hydroxides, and amine compounds such as triethylamine.

The content of the surfactant is preferably 0.1 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the magnetic particles. By including a surfactant in the composition, it becomes possible to disperse the magnetic particles more stably.

[Method of producing the composition]
The method for producing the composition will be exemplified below, but is not limited to the following method. The method for producing the composition preferably includes a step of producing magnetic particles and a step of dispersing the magnetic particles.

- Process for producing magnetic particles Magnetic particles can be produced by a liquid phase method. Specifically, an alkaline aqueous solution is added to an aqueous solution of the metal salt of the metal that constitutes the magnetic particles to neutralize it, a coprecipitate is produced, and the coprecipitate is heated and reacted to obtain a suspension solution. The initial salt concentration is important for producing magnetic particles. When the aqueous solution of the metal salt and the aqueous solution of the alkaline are mixed, the reaction of particle formation starts. At that time, if the salt concentration is high, particle formation occurs continuously and the grain size increases, so it is preferable to have a low salt concentration when producing magnetic particles.

After the reaction is complete, the suspension is washed with deionized water. Examples of washing methods include decantation, centrifugation, and ultrafiltration. Washing is continued until the salt concentration in the removed suspension is 100 ppm or less. After washing, a high-concentration magnetic particle paste is obtained by centrifugation, heating, vacuum drying, etc.

- Process for dispersing magnetic particles By adding an aqueous solution containing polyacrylic acid or a salt thereof, which is a dispersant for magnetic particles, to the obtained magnetic particle paste, the dispersant is directly attached to the surface of the magnetic particles, and the magnetic particles can be dispersed in water. Since some of the carboxyl groups of the magnetic particles are chemically adsorbed and other carboxyl groups are ionized, the magnetic particles have a dispersing function in water and are stably dispersed in an aqueous medium. Since the magnetic particles and the carboxyl groups are chemically adsorbed and the detachment of the carboxyl groups from the magnetic particles is unlikely to occur, it is believed that thickening can be suppressed. In addition, the concentration of the magnetic particles in the composition can be increased, improving the driving force for transporting heat.

Examples of dispersing machines used to disperse magnetic particles include two-roll mills, three-roll mills, ball mills, pebble mills, Henschel mixers, bead mills, Cobol mills, Tron mills, sand mills, sand grinders, segmented barrier lighters, high-speed impeller dispersers, high-speed stone mills, high-speed impact mills, dispersers, high-speed mixers, nanomizers, homogenizers, and ultrasonic dispersers. There are no particular restrictions on the dispersing conditions, which vary depending on the equipment actually used, but they may be set appropriately so that a uniform dispersion is formed depending on the type and concentration of the magnetic particles to be treated, the type and concentration of the dispersant, and the amount of processing. In addition, excess dispersant may be removed by washing after dispersion.

[Viscosity of the composition]
As described above, the viscosity of the composition affects the flow resistance when flowing through the flow path, and as a result, the flow rate of the composition decreases, and the amount of heat transport decreases. Therefore, it is preferable that the viscosity of the composition of the present invention is low. Specifically, the viscosity of the composition at 25°C is preferably 1.5 mPa·s or more and 30 mPa·s or less. In addition, the viscosity of the composition at 25°C is more preferably 20 mPa·s or less, and even more preferably 10 mPa·s or less. Here, the viscosity of the composition can be measured by a rotational viscometer.

[Heat transport device]
Fig. 1 is a diagram for explaining the principle of heat transport by the composition of the present invention. The principle of heat transport by the composition of the present invention will be explained in detail below. The heat transport device has a flow path 11 through which the composition 1 flows, a magnetic field application section 23 that applies a magnetic field to the composition 1, and a heating section 22 that heats a part of the composition 1 (see Fig. 1(a)). Here, in Fig. 1, the direction in which the composition flows in the flow path is indicated by an arrow X.

In FIG. 1(a), when a magnetic field H is applied to the composition 1 by the magnetic field application unit 23, the composition 1 behaves as a fluid having magnetization M. Here, a magnetic volume force F (M· _▽ H) proportional to the magnetization M and the magnetic field gradient _▽ H acts on the composition to which the magnetic field H is applied. Before heating, the magnetic volume forces F1 and F2 acting on the composition are balanced with the center (dotted line portion) of the magnetic field application unit 23 as a boundary, and the composition does not flow (see FIG. 1(b)). However, during heating, the magnetic volume force F2 acting on the right side of the center of the magnetic field application unit 23, that is, on the composition heated by the heating unit 22, becomes smaller due to the decrease in magnetization M of the magnetic particles due to heating. As a result, during heating, the magnetic volume force F1>magnetic volume force F2, and the composition flows in the X direction.

Figure 2 is a schematic diagram showing an example of the heat transport device of the present invention. The heat transport device has a flow path 11 through which the composition 1 flows, a magnetic field application section 23 that applies a magnetic field to the composition 1, and a heating section 22 that heats a part of the composition 1. The heat transport device preferably further has a cooling section 24, a flow meter 25, and a temperature sensor 28. The temperature sensor 28 is preferably a thermocouple made of two different metal conductors. In addition, the heating section 22 is preferably connected to a voltage/current source 27, and the flow meter 25 and the temperature sensor 28 are preferably connected to a display device 29. In addition, the flow path 11 is preferably connected by a connector 26.

The flow path 11 is made of copper pipes, aluminum pipes, Teflon (registered trademark) tubes, silicon tubes, rubber tubes, etc. It is preferable to use different materials for the flow path depending on the location in the device. In places where heat is input and output, such as the heating unit 22 and the cooling unit 24, it is possible to input and output heat efficiently by using flow paths with excellent thermal conductivity such as copper pipes or aluminum pipes. In other places, it is preferable to use Teflon tubes, which can be freely piped and can reduce flow resistance and increase flow rate.

Figure 3 is a schematic diagram showing in detail the magnetic field application section of the heat transport device in Figure 2. Here, the magnetic field application section 23 is arranged so that the magnets 13 face each other across the flow path 11. The magnetic field application section 23 is arranged so that there is one maximum point of the magnetic field strength. Examples of the magnets 13 used in the magnetic field application section include permanent magnets and electromagnets. In particular, as shown in Figure 3, the magnetic field application section 23 includes a permanent magnet magnetic circuit including the magnet 13 and a yoke 14, which is an iron core for connecting two magnets, the N pole and the S pole, with magnetic flux, thereby forming a heat transport device that enables heat transport by heating alone without using an external power source. Also, in Figure 3, a part of the flow path 11 is configured to be the heating section 22.

The heating unit 22 applies a temperature gradient to the composition 1 within the flow path 11. Examples of the heating means of the heating unit include an electric heater, an air heater, and a lamp heater. It is preferable that a portion of the heating unit 22 faces the magnetic field application unit 23 via the flow path 11.

Figure 5 is a diagram illustrating an example of a transportation device in which the heat transport device described in Figure 3 is incorporated into a cooling system for an electric vehicle. Examples of transportation devices include vehicles, ships, elevators, and belt conveyors. In the following, a vehicle equipped with wheels as a drive mechanism is used as an example, but the invention is not limited to this and may be any transportation device equipped with various drive mechanisms.

The electric vehicle cooling system mounted on an electric vehicle 30, which is a transport device, is composed of a drive motor 31, magnetic fluid 1 as a refrigerant, a reservoir 32 that temporarily stores the magnetic fluid 1, a cooler 33 that cools the magnetic fluid 1, and a flow path 34 that connects these. The electromagnet in the drive motor 31, which is provided on the body (frame) and serves as a heating unit (heat source), generates heat when the motor is driven. Note that the heating unit provided on the body includes not only those that are provided directly on the exterior of the vehicle, but also those that are attached via members to the internal space covered by the exterior.

The magnetic properties of the magnetic fluid 1 decrease as a result of receiving this heat, and a flow is generated by the magnetic force of the electromagnets in the motor.

The magnetic fluid 1 that receives heat from the drive motor 31 passes through the reservoir 32 and the cooler 33 to remove the heat, and circulates again as a refrigerant for the drive motor 31.

Furthermore, in electric vehicles, cooling of inverters such as IGBTs, batteries, etc. may be required. These generate heat when driven, so cooling is required to keep them at an appropriate temperature, but since the appropriate temperature for each is different, simply arranging them in series may not be desirable. The heat transfer device using this magnetic fluid can be arranged in parallel, as shown in FIG. 5. In FIG. 5, the magnetic fluid 1 cooled by the cooler 33 branches into the flow paths of the drive motor 31 and inverter 35, receives the heat generated by the drive motor 31 and inverter 35, merges in the reservoir 32, is cooled again by the cooler 33, and circulates. A magnet 36 is placed near the heat generating part of the inverter section to drive the magnetic fluid. It is also possible to branch it to cool the battery 37. A magnet 36 is also placed near the heat generating part of the battery section. By adjusting the strength of the magnet 36 placed near the heat generating part of the inverter 35 and battery 37 and the flow resistance of the flow path, it is possible to adjust the flow rate to be optimal for the drive motor 31, inverter 35, and battery 37.

In another embodiment of the present invention, a heat transport mechanism may be configured that includes a flow path 11 through which the composition 1 flows, and a magnetic field application unit 23 that applies a magnetic field to the composition 1. It may further include a cooling unit 24, a flow meter 25, and a temperature sensor 28. In other words, the heat transport mechanism does not include a heating unit (heat source) itself, but is a mechanism that assumes that the heating unit (heat source) is included on the side of the device on which the heat transport device is mounted.

Conversely, the above-mentioned heat transport device may be constructed by further arranging a heating section (heat source) in addition to the heat transport mechanism. For example, the above-mentioned transport equipment includes a heat transport mechanism, a heating section (heat source) such as a drive motor, a body, and a drive mechanism such as wheels.

The heat transport device using this magnetic fluid requires no electricity and has a small number of parts, making it suitable for use in cooling systems for electric vehicles. This cooling system can also be used in vehicles equipped with both an internal combustion engine and a motor, such as hybrid vehicles.

Other application examples of this heat transport device and heat transport mechanism include internal combustion engines of automobiles, solar power generation panels, large displays, large speakers, semiconductors such as CPUs and GPUs, and electrical boards that use these. In other words, it can be applied to a variety of devices that have a heating part (heat source). The present invention also includes devices such as solar panels, where the heating part (heat source) is a part whose temperature has risen due to radiant heat or heat transmission from another heat source.

The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited in any way to the following examples as long as the gist of the invention is not exceeded. Note that "parts" in the descriptions of component amounts refer to "parts by mass."

(Preparation of Compositions 1 to 12)
As shown in Tables 1 and 2, sodium hydroxide was dissolved in water to prepare an alkaline aqueous solution. Also, each of the metal salts shown in Tables 1 and 2 was dissolved in water to prepare an aqueous metal salt solution.

Next, while stirring the sodium hydroxide aqueous solution, each metal salt aqueous solution was dropped at a rate of 2 mL/min to react and produce ferrite particles. The pH of the resulting ferrite particles was adjusted to 11-12 using sodium hydroxide aqueous solution. The resulting suspension was then aged at a temperature of 90°C or higher for 1 hour to obtain a suspension of ferrite particles. The pH of the resulting suspension of ferrite particles was adjusted to 7, and washing with water by magnetic precipitation was repeated. Washing with water was continued until the washing solution no longer became cloudy even when barium chloride aqueous solution or silver chloride aqueous solution was added. The washed particles were concentrated by centrifugation to obtain a magnetic particle paste.

To the obtained magnetic particle paste, sodium polyacrylate, which is a dispersant as described in Tables 1 and 2, and water were added, and the mixture was dispersed using a homogenizer for 6 hours. The concentration of the magnetic particles was then adjusted to obtain each composition. In Tables 1 and 2, the amount of sodium polyacrylate is the solid content.

For sodium polyacrylate 1, T-50 (manufactured by Toa Gosei) with a solid content of 40% by mass was used, and the weight-average molecular weight was 6,000. For sodium polyacrylate 2, one prepared by a general method was used, and the weight-average molecular weight was 5,500. For sodium polyacrylate 3, A-210 (manufactured by Toa Gosei) with a solid content of 40% by mass was used, and the weight-average molecular weight was 3,000. For sodium polyacrylate 4, AC-10P-1 (manufactured by Toa Gosei) with a solid content of 40% by mass was used, and the weight-average molecular weight was 9,000. For sodium polyacrylate 5, one prepared by a general method was used, and the weight-average molecular weight was 20,000.

[Method for measuring weight average molecular weight]
The weight average molecular weight of the dispersant was measured by gel permeation chromatography (GPC) as follows. The resin was dissolved in tetrahydrofuran (THF) at 25° C. for 24 hours. The obtained solution was filtered through a membrane filter to obtain a sample solution. The sample solution was adjusted so that the concentration of the THF-soluble component was about 0.3%. Using this sample solution, the weight average molecular weight of the dispersant was measured under the following conditions.
Apparatus: Waters 2695 Separations Module, Waters RI detector: 2414 detector, Waters column: 4 KF-806M columns, Showa Denko eluent: tetrahydrofuran (THF)
Flow rate: 1.0mL/min
Oven temperature: 40°C
Sample injection volume: 100 μL

When calculating the weight average molecular weight of the dispersant, a molecular weight calibration curve was used that was created using standard polystyrene resins (TSK Standard Polystyrene F-850, F-450, F-288, F-128, F-80, F-40, F-20, F-10, F-4, F-2, F-1, A-5000, A-2500, A-1000, A-500, manufactured by Tosoh Corporation).

Tables 3 to 5 show the composition of the magnetic particles in each composition, the content (parts) of the magnetic particles in the composition, the content (parts) of the dispersant, the content (parts) of the surfactant, and the content (parts) of the water in the composition. All contents are solid content amounts. In addition, the lower part of Tables 3 to 5 shows the viscosity (mPa·s) as a characteristic of the composition, and the cumulative 50% particle size D ₅₀ (nm) on a volume basis as a characteristic of the particles. In Tables 3 to 5, Acetylenol E100 is a nonionic surfactant manufactured by Kawaken Fine Chemicals.

[Method of measuring viscosity]
The viscosity of the composition was measured at 25° C. using a rotational viscometer (RE80 type rotational viscometer, manufactured by Toki Sangyo Co., Ltd.).

[Method of measuring _D50 ]
The _D50 of the particles is a value measured using a particle size measuring device (Nanotrac 150, manufactured by Microtrac) by dynamic light scattering. The measurement conditions are: number of measurements: 3, measurement time: 120 seconds.

(Preparation of Composition 13)
A magnetic particle paste was obtained in the same manner as for compositions 1 to 12. Water was added to the obtained magnetic particle paste to make 600 g, and the temperature was increased to 95° C. to obtain a solution containing magnetic particles. Also, 6.8 g of 3-mercaptopropionic acid was dissolved in 150 mL of water, and the temperature was increased to 60° C. to obtain a solution containing 3-mercaptopropionic acid.

While stirring the solution containing the magnetic particles, a solution containing 3-mercaptopropionic acid was added and reacted at 95°C for 1 hour to allow the magnetic particles to adsorb 3-mercaptopropionic acid. After that, water washing by magnetic precipitation was repeated to remove excess 3-mercaptopropionic acid, and the magnetic particles were concentrated and dried until the solid content was 90% by mass, yielding 33 g of dried magnetic particles.

32 g of dried magnetic particles were added to a solution of 2 g of 24% aqueous sodium hydroxide dissolved in 20 g of water, and the mixture was stirred at high speed for 30 minutes to disperse the magnetic particles. The mixture was then concentrated by magnetic precipitation to obtain composition 13, which contains 45.0 parts of magnetic particles.

(Preparation of Composition 14)
A magnetic particle paste was obtained in the same manner as in compositions 1 to 12. Water was added to the obtained magnetic particle paste to make 500 g, and the temperature was then increased to 80° C. to obtain a solution containing magnetic particles. 20 g of sodium oleate was added while stirring the solution containing the magnetic particles. The solution was stirred at a temperature of 80° C. for 30 minutes to allow sodium oleate to be adsorbed onto the magnetic particles. Thereafter, heating was stopped, and hydrochloric acid was added to neutralize the solution and adjust the pH to 6.5 to 7, obtaining magnetic particles with sodium oleate adsorbed thereto.

The magnetic particles obtained were repeatedly washed with water by magnetic precipitation. The washing was continued until the washing liquid no longer became cloudy even when an aqueous solution of barium chloride was added. The particles were then dehydrated using a centrifugal dehydrator to obtain 42 g of hydrous magnetic particles with a solid content of 70%.

50 g of water and 18 g of 50% aqueous sodium dodecylbenzenesulfonate solution were uniformly stirred, and 20 g of the resulting hydrous magnetic particles were added to obtain composition 14, which contains 20.0 parts of magnetic particles.

(Preparation of Composition 15)
A composition was prepared in the same manner as in composition 14, to obtain composition 15 having a magnetic particle content of 30.0 parts.

(Preparation of Compositions 16 and 17)
Compositions were prepared in the same manner as in compositions 1 to 12, to obtain composition 16 having a magnetic particle content of 17.0 parts and composition 17 having a magnetic particle content of 30.0 parts.

(Composition 18)
Ferricolloid TS-50K (manufactured by Ichino Chemicals) based on kerosene, an oil-based medium, was used as the magnetic particles. The viscosity of the composition was 13.1 mPa·s, and the D ₅₀ of the particles was 11 nm.

Table 6 lists the alkaline aqueous solution (parts), metal salt aqueous solution (parts), and dispersant (parts) used in preparing the compositions. Table 7 lists the magnetic particle configuration in each composition, the magnetic particle content (parts), dispersant content (parts), surfactant content (parts), and water content (parts) in the composition. All contents are solid content amounts. In addition, the lower part of Table 7 lists the viscosity (mPa·s) as a characteristic of the composition, and the cumulative 50% particle size D ₅₀ (nm) on a volume basis as a characteristic of the particles.

(Preparation of Compositions 19 to 26)
Compositions 19 to 26, each having a magnetic particle content of 35.0 parts, were prepared in the same manner as in the case of compositions 1 to 12, to obtain compositions 19 to 26.

Tables 8 and 9 show the composition of the magnetic particles in each composition, the content (parts) of the magnetic particles in the composition, the content (parts) of the dispersant, the content (parts) of the water-soluble organic solvent, and the content (parts) of water in the composition. In addition, the lower part of Tables 8 and 9 shows _F25 - _F90 (gF) and viscosity (mPa·s) as composition properties, and volume-based cumulative 50% particle diameter _D50 (nm) as a particle property.

(Preparation of Compositions 19 to 26)
Compositions 19 to 26, each having a magnetic particle content of 35.0 parts, were prepared in the same manner as in the case of compositions 1 to 12, to obtain compositions 19 to 26.

Tables 8 and 9 show the composition of the magnetic particles in each composition, the content (parts) of the magnetic particles in the composition, the content (parts) of the dispersant, the content (parts) of the water-soluble organic solvent, and the content (parts) of water in the composition. In addition, the lower part of Tables 8 and 9 shows _F25 - _F90 (gF) and viscosity (mPa·s) as composition properties, and volume-based cumulative 50% particle diameter _D50 (nm) as a particle property.

The compositions exemplified below contain 10 to 50 parts by mass of glycol or glycerin per 100 parts by mass of the composition.

<Evaluation>
In the present invention, in the following evaluation criteria, A or B was determined as an acceptable level, and C was determined as an unacceptable level. The evaluation results are shown in Table 10.

(Storage stability)
10 mL of each composition obtained was placed in a glass sample tube (volume 30 mL, outer diameter 30 mm × height 63 mm, bottom area ⁵ cm2) and sealed. After leaving the tube undisturbed for 3 days, the dispersion state of the magnetic particles was visually observed to evaluate storage stability.
A: No change in state was observed. B: Gelled, but redispersed. C: Gelled, but not redispersed.

(Flow rate)
The heat transport device shown in Fig. 1 was prototyped and a drive test of the composition was performed. As the magnetic field application section, as shown in Fig. 3, two neodymium magnets of 60 x 30 x 30 tmm with an easy magnetization axis perpendicular to the flow channel 11 and magnetized in opposite directions, and two magnetic circuits made of yoke material SS400 of 70 x 30 x 10 tmm were arranged with the same poles. Here, the magnetic circuits were arranged to face each other with the flow channel 11 in between.

The flow path 11 was a Teflon (registered trademark) tube with an inner diameter of 4 mm, and the heating section was a copper tube with an inner diameter of 4 mm and a length of 40.0 mm, with the total length of the flow path 11 being 1200 mm.

As shown in Figure 3, the heating section was made of a copper tube whose relative position to the magnetic circuit could be freely changed, and was connected to a DC power source. The temperature of the copper tube was measured using a thermocouple, which acts as a temperature sensor, and the current and voltage were adjusted so that the measured value was between 25°C and 90°C. Each composition was sealed in the flow path to create a heat transport device.

The temperature of the composition in the flow path when not heated was set to 25°C, and a heat transport device was used to change the copper tube temperature (the temperature applied to the composition) to perform a composition drive test and measure the flow rate.

In Comparative Example 1, the composition had an unacceptable storage stability level of C, and the difference in flow rate (mL/min) at 60°C and 80°C was lower than in the Examples. In Comparative Examples 2 and 3, the composition had an unacceptable storage stability level of C, and the flow rates at 60°C and 80°C were both 0.0. This indicates that the driving force for heat transport was reduced due to the reduced storage stability of the compositions in Comparative Examples 1 to 3.

In Reference Examples 1 and 2, the composition had an acceptable storage stability level of A, but the flow rates at 60°C and 80°C were both 0.0. This indicates that the content of magnetic particles in the composition was small, and the driving force for heat transport was reduced.

In Reference Example 3, the storage stability of the composition was at an acceptable level, Class A, but the difference in flow rate (mL/min) between 60°C and 80°C was lower than in the Examples. This indicates that the medium in the composition was an oil-based medium, so the flow rate was low and the amount of heat transport was not large. In Comparative Example 6, the water content was low, so the dispersant did not function sufficiently and the magnetic fluid could not be dispersed in the medium.

Claims (16)

A composition comprising particles , a dispersant, and an aqueous medium containing water,
The particles include magnetic particles represented by the following formula (1):
The dispersant comprises polyacrylic acid or a salt thereof;
A composition characterized in that the weight average molecular weight of the dispersant is 4,500 or more and 7,000 or less .
(MnO) _x ・(ZnO) _y ・(Fe ₂ O ₃ ) _z ...Formula (1)
Here, x, y, and z satisfy 0.15≦x≦0.40, 0.10≦y≦0.25, 0.48≦z≦0.60, and x+y+z=1. The composition according to claim 1, wherein the particles have a cumulative 50% particle size based on volume of 200 nm or less. 3. The composition according to claim 1, wherein the content of the magnetic particles is 20.0 parts by mass or more and 50.0 parts by mass or less, based on the total mass of the composition. The composition according to claim 1 , wherein the content of the dispersant is 1.0 part by mass or more and 20.0 parts by mass or less based on the total mass of the composition. The composition according to claim 4 , wherein the content of the dispersant is 1.0 part by mass or more and 8.0 parts by mass or less based on the total mass of the composition. The composition according to claim 1 , wherein the content of the aqueous medium is 30.0 parts by mass or more and 80.0 parts by mass or less based on the total mass of the composition. the aqueous medium contains a water-soluble organic solvent,
The composition according to claim 1 , wherein the content of the water-soluble organic solvent is 10 parts by mass or more and 100 parts by mass or less with respect to 100 parts by mass of the water. The composition according to claim 1 , wherein the viscosity of the composition is from 1.5 mPa·s to 30 mPa·s. 9. The composition according to claim 1, wherein the magnetic particles contain at least two elements selected from the group consisting of Zn, Mn, Fe, Ni, Sr, Mg, and Ca. The composition according to claim 1 , comprising 10 to 50 parts by mass of glycol or glycerin per 100 parts by mass of the composition. 11. The composition of claim 10 , wherein the glycol is ethylene glycol or propylene glycol. A heat transport mechanism comprising: a flow path through which a composition flows; and a magnetic field application unit that applies a magnetic field to the composition, the composition being the composition defined in claim 1 . The heat transport mechanism according to claim 12 , further comprising a cooling section for cooling a portion of the composition. A heat transport mechanism according to claim 12 or 13 ,
A heat transport device having a heat source for heating a portion of said composition. The heat transport device according to claim 14 ;
The structure and
A transportation device equipped with a drive mechanism. An apparatus comprising the heat transport mechanism according to claim 12 or 13 .

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