JP7551445B2 - 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 a 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 enough to match the size of the electronic device and has a high driving force for transporting heat.

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 were applied to the magnetic fluid drive device described in Patent Document 1, the change in magnetization of the magnetic particles contained in the magnetic fluid due to temperature changes was small, and a high driving force for transporting heat could not be obtained. This resulted in a small amount of heat transport.

Therefore, an object of the present invention is to provide a composition having a high driving force for transporting heat. Another object of the present invention is to provide a heat transport device using the composition.

The present invention relates to a composition comprising particles including magnetic particles, a dispersant , and an aqueous medium,
the magnetic particles contain at least two or more elements selected from the group consisting of Zn, Mn, Fe, Ni, Sr, Mg, and Ca;
the dispersant comprises a polycarboxylic acid or a salt thereof,
the dispersant is present in an amount of 5 parts by mass or more and 100 parts by mass or less with respect to 100 parts by mass of the magnetic particles,
The composition is characterized in that the relationship between the attractive force F ₂₅ with which a magnet attracts the composition at 25° C. and the attractive force F ₉₀ with which a magnet attracts the composition at 90° C. satisfies F ₂₅ -F ₉₀ ≧10 g force.
The present invention also provides a method for producing a composition comprising particles including magnetic particles, a dispersant, and an aqueous medium, the method comprising the steps of:
A step of preparing magnetic particles containing two or more elements selected from the group consisting of Zn, Mn, Fe, Ni, Sr, Mg, and Ca;
Providing a dispersant containing a polycarboxylic acid or a salt thereof;
preparing a mixture by mixing the magnetic particles, the dispersant, and the aqueous medium such that the amount of the dispersant is 5 parts by mass or more and 100 parts by mass or less with respect to 100 parts by mass of the magnetic particles;
obtaining the composition from the mixture;
The present invention relates to a method for producing a composition comprising the steps of:

The present invention also relates to a heat transport mechanism comprising a heat transport device having a flow path through which a composition flows, a magnetic field application unit that applies a magnetic field to the composition, and a heating unit that heats a portion of the composition, wherein the composition is the above-mentioned composition .

The present invention provides a composition having a high driving force for transporting heat, and a heat transport device using the composition.

FIG. 1 is a diagram illustrating a method for measuring the attractive force with which a magnet attracts a 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. 4 is a schematic diagram showing in detail a magnetic field application unit of the heat transport device of FIG. 3. FIG. 4 is a diagram showing an example of a transport device incorporating the heat transport device of FIG. 3 . 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 an oil-based medium is used as a medium in the composition, there is a risk of fire if the oil-based medium leaks from a heat transport device exposed to high temperatures. In addition, when a composition containing magnetic particles is used for heat transport, in order to increase the amount of heat transport, it is necessary to increase the flow rate of the composition. 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 aqueous medium has a low viscosity. Therefore, by using an aqueous medium as a medium for dispersing magnetic particles, the viscosity of the composition itself can be reduced. Furthermore, 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.

In the present invention, the relationship between the attractive force F ₂₅ of the magnet at 25° C. and the attractive force F ₉₀ of the magnet at 90° C. satisfies F ₂₅ -F ₉₀ ≧10 gF. Here, a method for measuring the attractive force acting on a composition will be described with reference to FIG. 1. 1.0 mL of composition 1 and an inert gas such as nitrogen or argon are put into a sample tube 2 (cross-sectional area of 5 cm ² ) and sealed, and a weight 8 is placed on the sample tube 2. The weight 8 is used to reduce the effect of buoyancy acting on the sample tube 2 in the hot water bath 7. In addition, the sample tube 2 is fixed to a ceramic plate 6, and a hot water bath 7 capable of adjusting the temperature of the composition 1 in the sample tube 2 is placed on the ceramic plate 6. The temperature in the hot water bath 7 can be measured using a thermometer, a thermocouple, or the like. Furthermore, a polystyrene foam 4 with a permanent magnet 5 fixed on one side is placed on an electronic balance 3, and the ceramic plate 6 is placed so that the distance between the permanent magnet 5 and the bottom surface of the sample tube 2 is 8 mm. Here, a circular magnet with a diameter of 30 mm and a surface magnetic flux density of 0.4 T is used as the permanent magnet 5. The polystyrene foam 4 is used to reduce the effect of the permanent magnet 5 on the electronic balance 3.

When measuring the attractive force _F25 of the composition by the magnet at 25°C, the temperature in the water bath is set to 25°C, and the sample tube containing composition 1 is left to stand in the water bath for 5 minutes to set the temperature of composition 1 to 25°C. After standing, the scale on the electronic balance is read. Next, the temperature in the water bath is set to 25°C, and an empty sample tube containing no composition is left to stand in the water bath for 5 minutes to read the scale on the electronic balance. The difference between the scale when the sample tube containing composition 1 is used and the scale when the empty sample tube is used is taken as _F25 .

When measuring the attractive force F ₉₀ with which a magnet attracts a composition at 90°C, F ₉₀ is calculated in the same manner as F ₂₅ , except that the temperature in the water bath is changed to 90°C.

By using magnetic particles that have a property that magnetization decreases with increasing temperature, a difference in magnetization occurs between the magnetic particles in composition 1 at 25°C and the magnetic particles in composition 1 at 90°C. That is, the magnetic particles in composition 1 at 25°C have a higher magnetization than the magnetic particles in composition 1 at 90°C. Therefore, composition 1 at 25°C is more easily attracted by magnet 5 than composition 1 at 90°C. As a result, the value measured on the electronic balance when composition 1 at 25°C is used is higher than the value measured on the electronic balance when composition 1 at 90°C is used. That is, the larger the value measured on the electronic balance, the larger the value of the attractive force F with which the magnet attracts the composition. In particular, if the difference between the value measured when composition 1 at 25°C is used and the value measured when composition 1 at 90°C is used is 10 g weight or more, the difference in magnetization between the magnetic particles in composition 1 at 25°C and the magnetic particles in composition 1 at 90°C becomes large. This provides a high driving force for transporting heat.

Even when the magnetic fluids described in Patent Documents 2 and 3 were used, the relationship between the attractive force F ₂₅ with which a magnet attracts a composition at 25° C. and the attractive force F ₉₀ with which a magnet attracts a composition at 90° C. was F ₂₅ -F ₉₀ <10 g force.

Each ingredient is described in detail below.

[Composition]
The composition of the present invention contains particles, including magnetic particles, and an aqueous medium.

<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)
Here, in 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, based on the total mass of the composition. If the content of the magnetic particles in the composition is less than 20.0 parts by mass, the total magnetization of the magnetic particles contained in the composition will be small, and the driving force for transporting heat may not be sufficient. If the content of the magnetic particles in the composition exceeds 50.0 parts by mass, the viscosity of the composition may increase due to the high concentration of solids, and the flow rate may decrease. It is more preferable that the content of the magnetic particles is 30.0 parts by mass or more and 40.0 parts by mass or less, based on the total mass of the composition.

<Dispersant>
The particles preferably contain a dispersant. The dispersant is capable of dispersing the magnetic particles in an aqueous medium. The dispersant is preferably a polycarboxylic acid-based dispersant. The polycarboxylic acid-based dispersant is capable of stably dispersing the magnetic particles due to electrostatic repulsion caused by the carboxyl group and steric hindrance caused by the use of a resin.

The polycarboxylic acid dispersant is preferably a polymer having a unit derived from a monomer selected from the group consisting of acrylic acid, methacrylic acid, and maleic anhydride, or a salt thereof. Here, a unit means a unit structure corresponding to one monomer. The unit constituting the polycarboxylic acid dispersant is preferably a unit derived from at least one monomer selected from the group consisting of acrylic acid esters, methacrylic acid esters, maleic acid esters, styrene, styrene sulfonic acid, and olefins. In particular, the polycarboxylic acid dispersant is preferably polyacrylic acid or a salt thereof.

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

The dispersant adheres to the magnetic particles and coats the particle surface, making it possible to stably disperse the magnetic particles in an aqueous medium. Here, coating the particle surface with the dispersant does not necessarily mean that the entire particle is covered, but may be partial, and the layer of dispersant that coats the particle does not have to be uniform.

The amount of dispersant used is preferably 5 parts by mass or more and 100 parts by mass or less, and more preferably 10 parts by mass or more and 50 parts by mass or less, per 100 parts by mass of magnetic particles. If the amount of dispersant is too small relative to the magnetic particles, the magnetic particles may not be able to be stably dispersed. 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 smaller flow rate of the composition and a smaller amount of heat transport of the composition.

The mass average molecular weight of the dispersant is preferably 3,000 or more and 20,000 or less. If the mass average molecular weight is less than 3,000, it may be difficult to stably disperse the magnetic particles. If the weight average molecular weight exceeds 20,000, the viscosity of the composition increases, and the flow resistance of the composition increases. This may result in a smaller flow rate of the composition, and a smaller amount of heat transport of the composition. 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 based on the total mass of the composition.

[Cumulative 50% particle diameter (D ₅₀ ) based on volume of particles]
The particle preferably has a volume-based cumulative 50% particle size ( _D50 ) of 200 nm or less. If _D50 exceeds 200 nm, the particles may be difficult to stably disperse. Also, _D50 is preferably 10 nm or more. If _D50 is less than 10 nm, the specific surface area of the particles becomes large and the particles are easily oxidized in an aqueous medium.

Here, when using the magnetic fluid described in Patent Document 2, it is necessary to use a large amount of sodium dodecylbenzenesulfonate, which contributes to the dispersion of magnetic particles, in order to stably disperse the magnetic particles. It is presumed that if the viscosity of a magnetic fluid with a large content of dispersant is adjusted to an appropriate value, the content of magnetic particles in the magnetic fluid will be small, and the total magnetization of the magnetic particles in the magnetic fluid will decrease, resulting in F ₂₅ -F ₉₀ < 10 g weight.

The _D50 of the particles in the magnetic fluid described in Patent Document 3 was a value exceeding 1 μm. It is presumed that the large _D50 of the particles results in the existence of parts in which multiple magnetic domains are randomly arranged in the magnetic particles, resulting in parts that are difficult to align by a magnetic field, reducing the magnetization of the magnetic particles themselves, resulting in _F25 - _F90 <10 g force.

[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 the D ₉₀ exceeds 500 nm, the particles may be difficult to disperse stably.

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

<Aqueous medium>
The aqueous medium preferably 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 a dispersant for dispersing the magnetic particles to the obtained magnetic particle paste, the dispersant is directly attached to the surface of the magnetic particles, making it possible to disperse the magnetic particles in water.

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. 2 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 unit 23 that applies a magnetic field to the composition 1, and a heating unit (heat source) 22 that heats a part of the composition 1 (see Fig. 2(a)). Here, in Fig. 2, the direction in which the composition flows in the flow path is indicated by an arrow X.

In FIG. 2(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) of the magnetic field application unit 23 as the boundary, and the composition does not flow (see FIG. 2(b)). However, during heating, the magnetic volume force F2 acting on the right side of the center of the magnetic field application unit, 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 3 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 4 is a schematic diagram showing in detail the magnetic field application section of the heat transport device of Figure 3. 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 4, 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, N and S poles, 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 4, a part of the flow path 11 is configured to become 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 the configuration of a transport device in which the heat transport device described in Figure 3 is incorporated into a cooling system for an electric vehicle. Transport devices include vehicles, ships, elevators, belt conveyors, etc. Below, a vehicle equipped with wheels as a drive mechanism is used as an example, but the transport device is not limited to this and may be 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.

In addition, in electric vehicles, it may be necessary to cool inverters such as IGBTs and other heat sources such as batteries. 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, it may not be desirable to simply arrange them in series. The heat transfer device using this magnetic fluid can be arranged in parallel, as shown in Figure 6. In Figure 6, the magnetic fluid 1 cooled by the cooler 33 branches into the flow paths of the drive motor 31 and inverter 35, receives 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 and heat transport mechanism using this magnetic fluid require no electricity and have a small number of parts, making them suitable for use in cooling systems for electric vehicles. This cooling system can also be used in hybrid vehicles, which are equipped with both an internal combustion engine and a motor.

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 part whose temperature has risen due to radiant heat or heat transmission from the outside serves as the heating part (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, 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 3, A-6114 (manufactured by Toa Gosei) with a solid content of 40% by mass was used, and the weight average molecular weight was 10,000. For sodium polyacrylate 4 to 6, those prepared by a general method were used, and the weight average molecular weights were 5,500, 9,000, and 50,000, respectively.

[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 configuration 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 water, and the content (parts) of methanol. All contents are solid content amounts. In the lower part of Tables 3 to 5, F ₂₅ -F ₉₀ (gF) and viscosity (mPa·s) are shown as the properties of the composition, and the volume-based cumulative 50% particle diameter D ₅₀ (nm) is shown as the property of the particles. In Tables 3 to 5, methanol is a type of water-soluble organic solvent.

[Method of measuring _F25 - _F90 ]
F ₂₅ -F ₉₀ (gF) was measured by the method shown in Figure 1. Specifically, the method is as follows. 1.0 mL of composition 1 and nitrogen gas were placed in a glass sample tube 2 (volume 30 mL, outer diameter Φ30 mm x height 63 mm, cross-sectional area 5 cm ² ) and sealed. Then, a weight of 300 g was placed on the sample tube. A neodymium magnet (outer diameter Φ30 mm x height 15 mm) having a surface magnetic flux density of 0.4 T was used as the permanent magnet 5, and this neodymium magnet was placed on one side of a 100 mm high polystyrene foam.

The sample tube 2 was fixed to a ceramic plate 6 having a thickness of 0.5 mm, and a plastic water bath 7 having a thickness of 1 mm was placed on the ceramic plate 6, which was capable of adjusting the temperature of the composition 1 in the sample tube 2. Furthermore, the ceramic plate 6 was placed so that the distance between the neodymium magnet 5 and the bottom surface of the sample tube 2 was 8 mm. A GH-300 (manufactured by A&D) was used as an electronic balance for measuring the gravitational force.

The temperature in the water bath was set to each temperature (25°C, 90°C), the composition was left to stand at each temperature for 5 minutes, and the scale on the electronic balance was read. This was done three times, and the average value of the scale at each temperature was calculated. Next, the temperature in the water bath was set to each temperature (25°C, 90°C), an empty sample tube in which no composition was enclosed was left to stand in the water bath for 5 minutes, and the scale on the electronic balance was read. From the average value of the scale at each temperature and the scale when measuring the empty sample tube, F ₂₅ (gF) and F ₉₀ (gF) were calculated, respectively, and the value of F ₂₅ -F ₉₀ (gF) was obtained.

[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 magnetic 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.

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 configuration of the magnetic particles in each composition, the content (parts) of the magnetic particles in the composition, the content (parts) of the dispersant, and the content (parts) of water. All contents are solid content amounts. In the lower part of Table 7, F ₂₅ -F ₉₀ (gF) and viscosity (mPa·s) are listed as the characteristics of the composition, and the cumulative 50% particle size D ₅₀ (nm) on a volume basis is listed as the characteristic of the particles.

(Composition 18)
Ferricoloid TS-50K (manufactured by Ichino Chemicals) based on kerosene, an oil-based medium, was used as the magnetic particles. _{F 25} -F ₉₀ was 8.8 gF, the viscosity of the composition was 13.1 mPa·s, and the D ₅₀ of the particles was 11 nm.

(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 configuration 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, in the lower part of Tables 8 and 9, F ₂₅ -F ₉₀ (gF), viscosity (mPa·s), and cumulative 50% particle diameter D ₅₀ (nm) on a volume basis are shown as the characteristics of the composition. 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 was defined as an acceptable level and C was defined as an unacceptable level. The evaluation results are shown in Table 10.

(Driving force)
A: F ₂₅ -F ₉₀ ≧10 gF. C: F ₂₅ -F ₉₀ <10 gF.

(Flow rate)
A heat transport device as shown in Fig. 3 was fabricated and a drive test of the composition was carried out. As the magnetic field application section, as shown in Fig. 4, 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 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. The total length of the flow path 11 was 1200 mm.

As shown in Figure 4, 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.

It is preferable that the difference in flow rate of the composition at 60°C and 80°C is 9.0 mL/min or more.

In Comparative Example 1, the driving force of the composition was at an unacceptable level C, and the difference in flow rate (mL/min) between 60°C and 80°C was lower than in the Examples. This is because the _D50 of the particles in the composition was as large as 1 μm, and there were parts in the magnetic particles where multiple magnetic domains were randomly arranged, resulting in parts that were difficult to align by a magnetic field, and the magnetization of the magnetic particles themselves was reduced. This indicates that the driving force for heat transport of the composition was reduced.

In Comparative Example 2, the driving force of the composition was at an unacceptable level C, and the difference in flow rate (mL/min) between 60°C and 80°C was 0.0. In order to stably disperse the magnetic particles, it is necessary to use a large amount of sodium dodecylbenzenesulfonate, which contributes to the dispersion of the magnetic particles. When the viscosity of a composition with a large content of dispersant is adjusted to an appropriate value, the content of magnetic particles in the composition becomes small, indicating that the driving force for heat transport is reduced.

In Comparative Example 3, like Comparative Example 2, sodium dodecylbenzenesulfonate was used as a dispersant for the magnetic particles. In an attempt to increase the driving force for heat transport, the concentration of magnetic particles in the composition was increased, but the composition gelled and did not flow.

In Comparative Examples 4 and 5, the driving force of the composition was at an unacceptable level C, and the difference in flow rate (mL/min) between 60°C and 80°C was 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 1, the driving force of the composition was at an unacceptable level C, and the difference in flow rate (mL/min) between 60°C and 80°C was lower than in the Examples. This indicates that the driving force for heat transport was reduced because the medium in the composition was an oil-based medium.

In Comparative Example 6, the water content was low, so the dispersant did not function adequately and the magnetic fluid could not be dispersed in the medium.

Claims (19)

A composition containing particles including magnetic particles, a dispersant , and an aqueous medium,
the magnetic particles contain two or more elements selected from the group consisting of Zn, Mn, Fe, Ni, Sr, Mg, and Ca;
the dispersant comprises a polycarboxylic acid or a salt thereof,
the dispersant is present in an amount of 5 parts by mass or more and 100 parts by mass or less with respect to 100 parts by mass of the magnetic particles,
A composition, wherein the relationship between the force of attraction _F25 with which a magnet attracts said composition at 25° C. and the force of attraction _F90 with which a magnet attracts said composition at 90° C. satisfies _F25 - _F90 ≧10 g force. The composition according to claim 1, wherein the weight average molecular weight of the dispersant is 3,000 or more and 20,000 or less. 3. The composition according to claim 1, wherein the particles have a cumulative 50% particle size on a volume basis of 200 nm or less. 4. 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 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 magnetic particles contain at least two elements selected from the group consisting of Zn, Mn, and Fe. 9. The composition of claim 1, wherein the magnetic particles are ferrite particles. The composition according to claim 1 , wherein the viscosity of the composition is from 1.5 mPa·s to 30 mPa·s. The composition according to any one of claims 1 to 10 , wherein the difference in flow rate of the composition at 60°C and 80°C is 9.0 mL/min or more. 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. 13. The composition of claim 12 , 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 14 , further comprising a cooling section for cooling a portion of the composition. A heat transport mechanism according to claim 14 or 15 ;
A heat transport device having a heat source for heating a portion of said composition. The heat transport device according to claim 16 ;
The structure and
A transportation device equipped with a drive mechanism. An apparatus comprising the heat transport mechanism according to claim 14 or 15 . A method for producing a composition containing particles including magnetic particles, a dispersant, and an aqueous medium, comprising the steps of:
A step of preparing magnetic particles containing two or more elements selected from the group consisting of Zn, Mn, Fe, Ni, Sr, Mg, and Ca;
Providing a dispersant containing a polycarboxylic acid or a salt thereof;
preparing a mixture by mixing the magnetic particles, the dispersant, and the aqueous medium such that the amount of the dispersant is 5 parts by mass or more and 100 parts by mass or less with respect to 100 parts by mass of the magnetic particles;
obtaining the composition according to any one of claims 1 to 13 from the mixture through
A method for producing a composition comprising:

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