Microcapsules for latent heat storage material and method for producing the same, powder containing the microcapsules for latent heat storage material, and heat storage device containing the powder

Abstract

To provide a microcapsule for a latent heat storage material with high durability.SOLUTION: A microcapsule for a latent heat storage material comprises a metal core containing Zn and Al and a shell that is in contact with the metal core and covers it, wherein the shell of the microcapsule contains Al, Zn and O and has a thickness of 1.0 μm or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to microcapsules for latent heat storage materials and a method for producing the same, a powder containing the microcapsules for latent heat storage materials, and a heat storage device containing the powder. [Background technology]

[0002] Heat storage techniques include sensible heat storage and latent heat storage. Sensible heat storage utilizes the temperature change of a heat storage medium, while latent heat storage utilizes the phase change of a heat storage medium, for example, from a solid phase to a liquid phase.

[0003] Patent Document 1 discloses a latent heat storage material, which is composed of a core particle of an Al-Si alloy and a shell of an Al oxide coating covering the core particle. Regarding the shell, Patent Document 1 discloses that the core particle is subjected to a chemical conversion coating treatment and then to a thermal oxidation treatment, thereby forming an oxide coating.

[0004] Patent Document 2 discloses that the core particles of the latent heat storage material are an alloy (AB alloy) of at least one alloy component A selected from the following Group A and at least one alloy component B selected from the following Group B: Group A: Ca, Si, Bi, Mg, Sb, In, Sn, Al, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Pd, Ag, Au, Pb Group B: Al, Cr, Mn, Si, Mg, Co, Ni Furthermore, Patent Document 2 discloses that the following relationship is satisfied: ΔG A 0 ≧ΔG B 0 (ΔG A 0 ): Standard free energy of oxide formation of the alloy component A (ΔG B 0 ): Standard free energy of oxide formation of the alloy component B

[0005] Patent Document 3 discloses a latent heat storage medium intended to reduce the occurrence of leakage from the core, and has a BET specific surface area of ​​10 m 2 / g or more. It also discloses the use of a specific amine compound during production, particularly during boehmite treatment.

[0006] Non-Patent Document 1 discloses the following three types of alloys. Zn 84 Al 8.7 Mg 7.3 , Zn 88.7 Al 11.3 , Zn 92.2 Mg 7.8 (Each number represents at.%) Non-Patent Document 1 discloses that the possibility of using these alloys as phase change materials for latent heat storage was evaluated. Furthermore, according to the document, the melting points are 344°C, 382°C, and 371°C, respectively, and the heats of fusion are 132 Jg -1 , 118Jg -1 , 106Jg -1 It is stated that it was. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2017 / 200021 [Patent Document 2] International Publication No. 2015 / 162929 [Patent Document 3] Japanese Patent Application Publication No. 2019-203128 [Non-patent literature]

[0008] [Non-Patent Document 1] E. Risue et al., “Zinc-rich eutectic alloys for high energy density latent heat storage applications,” Journal of Alloys and Compounds 705 (2017), p.714-721 Summary of the Invention [Problem to be solved by the invention]

[0009] The temperature range of automobile exhaust is wide, for example, from about 200°C during idling to about 800°C during full-load operation. Automobile exhaust systems are equipped with exhaust purification catalysts. However, if the exhaust temperature is too high, there is a possibility that the performance of the exhaust purification catalyst will decrease and / or deteriorate. Therefore, in order to suppress excessive increases in exhaust temperature, it is conceivable to install a latent heat storage material in the automobile exhaust system to perform heat exchange. On the other hand, if the exhaust temperature is too low, the performance of the exhaust purification catalyst will not be fully demonstrated. From the above perspectives, the present inventors have considered that excessive fluctuations in automobile exhaust temperature may be suppressed by using a latent heat storage material that has an appropriate operating temperature of about 300 to 550°C and an excellent latent heat capacity.

[0010] The inventors then considered using a combination of Al and Zn as a core material suitable for this temperature range, because by adjusting the ratio of Al to Zn, it is possible to adjust the melting point of the Al-Zn binary alloy to fall within the above temperature range.

[0011] However, the properties required of microcapsules for latent heat storage materials are not just the melting point temperature range of the core, but also the ability to maintain their structure even under repeated drastic temperature changes (repeated durability). The key to achieving this repeated durability is the properties of the shell. The shell is formed when some of the core components undergo chemical reactions during oxidation treatment.

[0012] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide highly durable microcapsules for latent heat storage materials. [Means for solving the problem]

[0013] As a result of extensive research, the inventors have found that a highly durable shell can be formed by reducing the rate of temperature rise. This is thought to be because a thick shell is formed by reducing the rate of temperature rise, and this thickness ensures durability. The present invention was completed based on this finding, and in one aspect, includes the following inventions.

[0014] (Invention 1) A microcapsule for a latent heat storage material, comprising a metal core containing Zn and Al and a shell that contacts and covers the metal core, The shell of the microcapsule contains Al, Zn, and O, The shell has a thickness of 1.0 μm or more. Microcapsules for latent heat storage materials. (Invention 2) The microcapsules for latent heat storage materials of Invention 1, wherein Zn is 60 to 95 parts by mass and Al is 5 to 40 parts by mass, assuming that the total mass of Al and Zn in the core of the microcapsule is 100 parts by mass. (Invention 3) 3. The microcapsules for latent heat storage materials according to Invention 1 or 2, wherein the shell has a thickness of more than 2.0 μm. (Invention 4) A powder containing a plurality of microcapsules for a latent heat storage material according to any one of Inventions 1 to 3. (Invention 5) The powder of invention 4, having an average particle size of 20 to 100 μm. (Invention 6) The powder of invention 5, having an average particle size of 30 to 50 μm. (Invention 7) A heat storage device comprising the powder according to any one of inventions 4 to 6. (Invention 8) The heat storage device according to invention 7, which is installed on the outer periphery of an exhaust passage of an automobile. (Invention 9) A method for producing microcapsules for latent heat storage materials according to any one of Inventions 1 to 3, which comprises sequentially subjecting Zn-Al alloy particles to boehmite treatment and oxidation treatment, in which the oxidation treatment involves heating the particles to a holding temperature at a heating rate of 6°C / min or less, and maintaining the particles at the holding temperature in an oxygen-containing atmosphere. (Invention 10) 10. The method according to claim 9, wherein the temperature rise rate is 4°C / min or less. (Invention 11) The method according to invention 9 or 10, wherein the holding temperature is 550°C to 850°C. [Effects of the Invention]

[0015] In one aspect, the microcapsules for latent heat storage materials of the present invention have a shell thickness of 1.0 μm or more, which improves the repetitive durability. [Brief explanation of the drawings]

[0016] [Figure 1] 1 shows a cross-sectional view of a microcapsule for a latent heat storage material in one embodiment (Example 1). The upper image is an SEM photograph, and the three lower images show EDS analysis results for the elements O, Al, and Zn, respectively. [Figure 2] An enlarged photograph of the photograph in Figure 1 is shown. DETAILED DESCRIPTION OF THE INVENTION

[0017] <1. Microcapsules for latent heat storage materials> (1-1. Overall composition of microcapsules) In one embodiment, the microcapsules for latent heat storage materials according to the present invention contain Al and Zn. The melting point of Al is 660.3°C, and the melting point of Zn is 419.5°C. Therefore, increasing the ratio of Zn to Al can lower the melting point of the microcapsules. Furthermore, despite the lower melting point, microcapsules containing Al and Zn have the characteristic of having a large latent heat per volume upon melting. Furthermore, because Al has a large volume expansion coefficient upon melting, adding Zn, which has a small volume expansion coefficient upon melting, can mitigate the volume expansion during the phase change from solid to liquid. However, if the ratio of Zn added to Al is too high, an AlOOH film, which serves as a precursor to an aluminum oxide film, is not sufficiently formed during the boehmite treatment. This is thought to make it difficult to form a sufficient aluminum oxide film during the subsequent oxidation treatment. Therefore, there is an appropriate content ratio of Al to Zn.

[0018] Therefore, in the core of the microcapsules for latent heat storage material according to a preferred embodiment of the present invention, the Zn content is 60 to 95 parts by mass, and the Al content is 5 to 40 parts by mass (wherein the total mass of Al and Zn in the core of the microcapsule is 100 parts by mass). In the core of the microcapsules for latent heat storage material according to a more preferred embodiment of the present invention, the Zn content is 60 to 90 parts by mass, and the Al content is 10 to 40 parts by mass. In the core of the microcapsules for latent heat storage material according to an even more preferred embodiment of the present invention, the Zn content is 60 to 80 parts by mass, and the Al content is 20 to 40 parts by mass.

[0019] The metal core may contain one or more third elements (e.g., Sn, Bi, Cu, In, Ni, etc.). However, in order to prevent unexpected changes in properties, the microcapsule preferably contains Zn and Al in total at 70% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, based on the total mass of the microcapsule. The microcapsule may be composed only of Zn and Al, excluding oxygen (O) and unavoidable impurities.

[0020] In relation to the ratio of Al to Zn described above, in one embodiment, the core volume expansion coefficient of the microcapsules for latent heat storage material according to the present invention upon melting is 5 to 9%, preferably 6 to 9%, and more preferably 7 to 9%. Within these ranges, the oxide film constituting the shell is less likely to be damaged even if physical forces acting on the shell are applied during repeated melting. The core volume expansion coefficient varies depending on the ratio of the constituent elements. For example, the volume expansion coefficient between the solidus temperature and the liquidus temperature can be calculated using Factsage (manufactured by Computational Mechanics Research Center, Ver. 7.3). For example, by setting conditions within the following range, the volume expansion coefficient of an Al-Zn binary alloy at a given composition ratio can be calculated. Database: FTlite ·Elements: Al, Zn Calculated composition: 5 to 40 wt% Al (in 5 wt% increments) Temperature: 0 to 600°C (in 1°C increments) Pressure: 1atm

[0021] In this specification, the volume expansion rate of the microcapsules for the thermal storage latent heat material when melted does not mean an actual measured value but a predicted result by software (Factsage).

[0022] (1-2. Microcapsule structure) In one embodiment, the microcapsules for latent heat storage materials according to the present invention have a metal core containing Zn and Al, and a shell that contacts and covers the metal core.

[0023] The metal core contains Zn and Al. In one embodiment, the Zn and Al in the metal core can be present in the form of a Zn—Al alloy (e.g., a binary alloy of Zn—Al).

[0024] In one embodiment, to prevent unexpected changes in properties, the metal core may contain Zn and Al in a total amount of 70% by mass or more, preferably 90% by mass or more, and more preferably 95% by mass or more. The metal core may be composed only of Zn and Al, excluding unavoidable impurities.

[0025] In one embodiment, the shell contains Al, Zn, and O. In particular, Al, Zn, and O are all detected in the shell region within 300 nm (preferably 200 nm) from the core. Here, the boundary between the core and the shell can be determined based on whether or not O is detected. Preferably, the shell contains several oxides. More specifically, the oxides contained in the shell can include Al2O3, ZnO, and ZnAl2O4. The presence of these oxides can be detected by analyzing a cross section of the microcapsule using EDS (energy dispersive X-ray spectroscopy) or AES (Auger electron spectroscopy). For example, by analyzing the shell of the microcapsule using EDS or AES and overlaying images of Zn, Al, and O, Al2O3, ZnO, and ZnAl2O4 are detected. Furthermore, an additional shell may be provided outside the shell containing Al, Zn, and O. Therefore, the number of layers provided in the microcapsule for latent heat storage material may be one, two, or more, or may be partially two or more. For the same thickness, the number of layers is preferably one because a single layer has higher durability.

[0026] The shell thickness (when the shell is a single layer, the thickness of the single layer; when the shell is composed of multiple layers, the total thickness of the multiple layers) is 1.0 μm or more, preferably more than 2.0 μm, and more preferably 2.5 μm or more. Ensuring a certain thickness allows the strength of the shell to be maintained. On the other hand, the upper limit is not particularly limited, but is typically 3.7 μm or less. In relation to the shell thickness, the microcapsules for latent heat storage materials of the present invention in one embodiment have excellent durability, particularly when subjected to repeated temperature changes from low to high temperatures. In some applications, the microcapsules for latent heat storage materials may be exposed to drastic temperature changes. Therefore, such excellent durability may be beneficial.

[0027] In this specification, the average thickness of the shell is measured by the following method. First, the cross section of the microcapsule is observed using an SEM, and the shell thickness is measured at three or more points per microcapsule, and the average of the measured values ​​is calculated. Then, similar measurements and calculations are performed on three or more microcapsules. Then, the average value for the average value of each microcapsule is calculated.

[0028] Here, the boundary between the shell and the core can be identified by performing elemental analysis of a cross-sectional view (e.g., EDS (Energy Dispersive X-ray Spectroscopy), AES (Auger Electron Spectroscopy), etc.) to confirm the presence or absence of oxygen.

[0029] (1-3. Melting point of microcapsules) In one embodiment, the melting point of the microcapsules for latent heat storage materials according to the present invention is 300 to 550°C. The optimum temperature for an automobile exhaust purification catalyst is approximately 400°C. Therefore, in order to maintain the automobile exhaust temperature at around this temperature, the melting point of the microcapsules is preferably 350 to 450°C, and more preferably 370°C or higher.

[0030] In this specification, the melting point of a microcapsule refers to the melting initiation temperature when differential scanning calorimetry (DSC) is carried out.

[0031] (1-4. Microcapsule size) In one embodiment, the microcapsules for latent heat storage materials according to the present invention are provided in the form of a powder containing a plurality of microcapsules for latent heat storage materials. In one embodiment, the average particle size of the powder is 20 to 100 μm, preferably 30 to 50 μm. If the average particle size is too small, it becomes difficult to ensure the required amount of heat storage. On the other hand, if the average particle size is too large, there is a high possibility that the particles will adhere to each other. This adhesion may occur due to leakage of core components that act as a binder. Therefore, there is a possibility that the shell structure may be damaged.

[0032] The average particle size described in this specification (e.g., the average particle size of the raw material powder and the average particle size of the powder containing the microcapsules for the latent heat storage material) is a value measured using a laser diffraction particle size distribution analyzer (e.g., HORIBA LA-920 or Microtrack Bell MT3000II). More specifically, the volume distribution of the particle group is measured using a laser diffraction particle size distribution analyzer, and the cumulative 50% volume diameter (D50) is regarded as the average particle size.

[0033] (1-5. Latent heat of microcapsules) In one embodiment, the latent heat quantity of the microcapsules for latent heat storage material according to the present invention is 70 to 130 J / g, and in a preferred embodiment, the latent heat quantity is 88 to 110 J / g.

[0034] In this specification, the latent heat of a microcapsule refers to the change in heat flow accompanying a solid-liquid phase change when differential scanning calorimetry (DSC) is performed.

[0035] In a further embodiment, the microcapsules for latent heat storage materials according to the present invention have excellent durability when subjected to repeated temperature changes. More specifically, the microcapsules for latent heat storage materials according to the present invention have a low rate of decrease in latent heat when subjected to repeated temperature changes.

[0036] The rate of decrease in latent heat quantity when temperature changes are repeated can be calculated, for example, by measuring under the following conditions. Heating rate and cooling rate: 50K / min Maximum temperature 600℃ Minimum temperature 350℃ atmosphere atmosphere Repeat 100 times Decrease rate of latent heat = (latent heat after 100 repetitions) ÷ (latent heat after 0 repetitions) × 100

[0037] In a further embodiment, the reduction rate of the latent heat quantity of the microcapsules for latent heat storage material according to the present invention calculated under the above conditions may be 95 to 105% (preferably 96 to 100%). Note that, although theoretically, it is unlikely to exceed 100%, in practice it may exceed 100% due to measurement errors, etc., so taking into account measurement errors, the practical upper limit may be 105%.

[0038] (1-6. Uses of Microcapsules) According to one embodiment of the present invention, a heat storage device is provided that includes powder containing microcapsules for latent heat storage materials. In the microcapsules for latent heat storage materials according to one embodiment of the present invention, the melting point can be easily adjusted to a range of approximately 300 to 550°C, preferably 370°C or higher, by varying the Zn content. Therefore, the microcapsules for latent heat storage materials are suitable for use in, for example, latent heat storage devices, which may be installed in the exhaust system of an automobile to adjust the exhaust temperature. In one embodiment, a heat storage device including powder containing microcapsules for latent heat storage materials can be installed around the exhaust passage of an automobile. Furthermore, the heat storage device can store not only automobile exhaust heat but also various types of unused heat generated within the above-mentioned temperature range.

[0039] <2. Method for manufacturing microcapsules for latent heat storage materials> The method for producing microcapsules for latent heat storage materials according to the present invention will be described below by way of example.

[0040] (2-1. Raw materials) First, Zn-Al binary alloy particles are prepared as raw materials. The content ratio of Al and Zn in the Zn-Al binary alloy particles can be adjusted appropriately depending on the required properties. Typically, the Zn-Al binary alloy particles are provided in the form of powder. In one embodiment, the average particle size of the raw material powder is 20 to 100 μm. From the viewpoint of forming a shell with few surface defects, the average particle size of the powder is preferably 20 to 50 μm. Furthermore, the Zn-Al composition ratio in the raw material may be set to a value close to the composition ratio required in the final product. Although the composition ratio may vary slightly by going through the manufacturing process described below, the variation is not significant. Therefore, by preparing and manufacturing several raw materials with similar composition ratios, microcapsules with the desired composition ratio can be easily obtained.

[0041] (2-2. Boehmite treatment) Next, the raw material Zn-Al binary alloy particles are subjected to boehmite treatment to form a coating. By performing the boehmite treatment, a precursor of the oxide coating that forms the shell can be formed. Specifically, the raw material Zn-Al alloy particles are placed in high-temperature water to form a coating on the alloy surface. The purity of the water is preferably high. Specifically, distilled water, pure water, deionized water, etc. can be used.

[0042] For example, Zn-Al alloy particles can be subjected to the boehmite treatment under conditions of a water temperature of 60 to 100°C for 3 to 12 hours. The boehmite treatment is preferably carried out with stirring. After the boehmite treatment, the liquid temperature may be lowered to room temperature by cooling, although this is not particularly limited. The particles after the boehmite treatment are then recovered, suction filtered, and dried. The reason for drying the particles after the boehmite treatment is to remove excess moisture from the particle surface. (2-3. Oxidation treatment) Next, the Zn-Al binary alloy particles that have been subjected to the boehmite treatment are subjected to an oxidation treatment. More specifically, high-temperature treatment is performed in an oxygen-containing atmosphere. By performing the oxidation treatment after the boehmite treatment, a shell having an oxide film can be formed.

[0043] The oxidation treatment is carried out at the holding temperature described below, but the temperature rise rate is slowed when the temperature is raised to the holding temperature. When the temperature rise rate is slowed to a certain level, the thickness of the shell itself increases. As a result, the strength of the shell increases.

[0044] Typically, the temperature rise rate may be 6°C / min or less, preferably 4°C / min or less. The lower limit is not particularly limited, and may be, for example, more than 0°C / min or 1°C / min or more. Such a temperature rise rate is also preferable from the viewpoint of mass production. For example, in mass production, a reactor having a physically large size is often used, and therefore, it is often difficult to achieve a rapid temperature change.

[0045] The oxygen-containing atmosphere may be any atmosphere containing oxygen, such as an oxygen atmosphere in which 99.5% pure oxygen is supplied at a flow rate of 200 mL / min, or an air atmosphere. From the viewpoint of mass production, an air atmosphere is preferable. The holding temperature may be, for example, 550 to 850°C, preferably 650 to 850°C.

[0046] The temperature rise rate is calculated using the following formula: Heating rate = (holding temperature - heating start temperature) / (time required to reach the holding temperature after heating start)

[0047] On the other hand, when the temperature is lowered from the holding temperature, the temperature lowering rate is not particularly limited and may be any rate, for example, the temperature lowering rate may be −1° C. / min to −60° C. / min, or may be −1° C. / min to −6° C. / min.

[0048] The time for maintaining the temperature can be, for example, 30 minutes to 10 hours, and preferably 1 hour to 5 hours.

[0049] The key to the oxidation treatment is to proceed with the oxidation reaction under mild conditions. For example, the oxidation reaction can be carried out under mild conditions by slowing the temperature rise rate and / or setting the atmosphere to air instead of pure oxygen. This allows the growth of the membrane thickness to be promoted while maintaining the microcapsule structure.

[0050] The scale of the oxidation treatment is not particularly limited, but for example, the amount of sample per batch is 5 g or more, and in the case of mass production, it is 50 g or more, preferably 75 g or more, and more preferably 100 g or more.

[0051] Here, "per batch" refers to the unit in which particles come into contact with each other. For example, in the case of a fluidized bed, it refers to one fluidized reaction bed. For example, in the case of a rotary kiln, it refers to the interior of one rotating rotary kiln. In the case of a roller hearth kiln, it refers to one sagger that is fed into the kiln (even if multiple saggers are fed at once, there is no possibility of particles in different saggers coming into contact with each other, so in the case of a roller hearth kiln, it refers to one sagger). [Example]

[0052] Examples of the present invention will be described below together with comparative examples. These examples are provided for a better understanding of the present invention and its advantages, and are not intended to limit the present invention.

[0053] Example 1 (1. Preparation of powder containing microcapsules for heat storage latent heat material) The powder containing the microcapsules for the thermal storage latent heat material of Example 1 was prepared by the following procedure.

[0054] (1-1. Raw material powder) First, a Zn-Al binary alloy powder (Zn-30% by mass Al) with a Zn mass ratio of 70% and an Al mass ratio of 30% was prepared by rotary disk atomization. The average particle size of the powder was measured using a laser diffraction particle size distribution analyzer (Microtrack Bell, MT3000II) and found to be 20-50 μm.

[0055] (1-2. Boehmite treatment) 300 mL of distilled water was placed in a beaker and heated. While stirring at 500 rpm using a hot stirrer, 10 g of the powder prepared above was added to the 300 mL of distilled water. Then, boehmite treatment was performed while continuing stirring. During the boehmite treatment, the amount of water in the beaker was maintained by adding distilled water.

[0056] (1-3. Oxidation treatment) The powder was then placed in a sample pan of a tabletop tubular furnace (Koyo Thermo Systems Co., Ltd., model: KTF055N). The amount of sample placed in one sample pan (i.e., the amount of sample per batch) was 5 g. Next, the powder was left to stand under atmospheric conditions with air supplied at a flow rate of 200 mL / min, and then oxidized. The conditions for the oxidation treatment in Example 1 were as follows: Heating rate: 3K / min Holding temperature: 700℃ Holding time: 1h Cooling rate: -50K / min

[0057] The temperature increase rate and the temperature decrease rate were calculated according to the following formula. Heating rate = (holding temperature - 25°C) / (time required to reach the holding temperature from 25°C) Cooling rate = (25°C - holding temperature) / (time required to reach 25°C from the holding temperature after starting cooling)

[0058] (2. Characterization) The powder containing the microcapsules for a thermal storage latent heat material of Example 1 obtained by the above procedure was subjected to the following property analysis.

[0059] (2-1. Cross-sectional observation using SEM) A groove was formed on the surface of the carbon piece using a cutter. A powder sample containing microcapsules for thermal storage latent heat material was embedded in the groove. Next, the surface and particles of the carbon piece were polished using a CP (cross section polisher) (more specifically, using an Ar ion beam) to expose the particle cross section. This particle cross section was then etched using Ar ions (etching conditions were as follows: beam energy 3000 eV, ion current 4.0 μm, gas pressure 8.0 × 10 -2 The particle cross sections were then observed using a SEM (Hitachi High-Technologies Corporation, Model SU-70).

[0060] As shown in FIG. 1, it was confirmed that the particles according to Example 1 had a shell formed on the particle surface that covered the metal core.

[0061] (2-2. EDS (Energy Dispersive X-ray Spectroscopy) Analysis) After forming a particle cross section using the method described in the previous section "(2-1. Cross-section observation by SEM)", EDS analysis (manufactured by Hitachi High-Technologies Corporation, Model SU-70) was carried out.

[0062] As a result, as shown in Figure 1, an oxide film containing Al, Zn, and O was formed in Example 1. Zn and Al were also detected in both the core and shell portions.

[0063] Overlaying the images of O, Al, and Zn showed that these three elements were present in the shell (including oxides such as Al2O3, ZnO, and ZnAl2O4).

[0064] Figure 2 shows an enlarged photograph of the cross section shown in Figure 1. As can be seen by comparing it with the 2.5 μm scale bar, the shell was significantly thicker, exceeding 2.5 μm. This was also the case in areas other than those shown in the enlarged photograph.

[0065] (2-3. Latent heat amount) The latent heat quantity of the microcapsules for the thermal storage latent heat material was determined by differential scanning calorimetry (DSC) (manufactured by Rigaku Corporation, model DSC8231). The latent heat quantity of the particles of Example 1 was 97 J / g.

[0066] (2-4. Durability test) The temperature was raised and lowered 100 times at a rate of 50 K / min. The maximum temperature was 600°C and the minimum temperature was 350°C. This was carried out in an air atmosphere. The latent heat was then measured according to the procedure described in the previous section "(2-3. Latent Heat Amount)". The rate of change in the amount of accumulated heat before and after the durability test was calculated according to the following formula. As a result, the rate of decrease in the latent heat of the particles of Example 1 was 101%. Decrease rate of latent heat = (latent heat after 100 repetitions) ÷ (latent heat after 0 repetitions) × 100

[0067] (2-5. Film Thickness Measurement) The cross section of the microcapsule was observed using an SEM, and the shell thickness was measured at four points for each microcapsule, and the average value was calculated. Similar measurements and calculations were performed on six microcapsules. The average value for each microcapsule was then calculated. As a result, the film thickness of the particles according to Example 1 was 3.4 μm.

[0068] (2-6. Volume expansion rate) The core volume expansion rate of the heat storage latent heat material microcapsules when melted was calculated based on the composition ratio of the raw material particles using Factsage (manufactured by Computational Mechanics Research Center, Ver. 7.3, conditions are as follows) between the solidus temperature and the liquidus temperature. As a result, the volume expansion rate of the particles according to Example 1 was 8.2%. Database: FTlite ·Elements: Al, Zn Calculated composition: 5 to 40 wt% Al (in 5 wt% increments) Temperature: 0 to 600°C (in 1°C increments) Pressure: 1atm

[0069] (2-7.Average particle size) The average particle size of the microcapsules for the thermal storage latent heat material was measured using a laser diffraction particle size distribution analyzer (Microtrack Bell, MT3000II). As a result, the particle size of the particles according to Example 1 was 42.5 μm.

[0070] (2-8. Melting Point) The melting point of the microcapsules for the thermal storage latent heat material was determined by differential scanning calorimetry (DSC) (manufactured by Rigaku Corporation, model DSC8231), and the result was that the melting point of the particles according to Example 1 was 377°C.

[0071] (2-9. Mass ratio of Al and Zn in microcapsules) The microcapsules for thermal storage latent heat material were crushed so as to destroy the core / shell structure. The crushed samples were analyzed using an X-ray diffractometer (Rigaku, model SmartLab). The results were then subjected to quantitative analysis using the RIR (Reference Intensity Ratio) method to determine the mass ratio of Zn and Al. For example, the mass ratio of Al was calculated as Al / (Al + Zn) × 100. Note that the mass ratio of Zn and Al referred to here refers to the mass ratio of pure Zn and pure Al. In other words, it does not include Zn compounds (e.g., oxides) or Al compounds (e.g., oxides). As mentioned above, the boundary between the core and shell can be determined based on whether or not O is detected. Therefore, although the object to be crushed and analyzed includes the shell and core, the detected pure Zn and pure Al are essentially derived from the core.

[0072] The RIR values ​​used were those listed in the Powder Diffraction File (PDF) database of the International Diffraction Data Center. The analytical conditions were set as follows: ·X-ray source: CuKα ray Measurement range: 2θ=10°~120° Step: 0.01° Scan speed: 20.0° / min Detector: High-speed one-dimensional detector D / teX Ultra Tube voltage: 40kV ·Tube current: 30mA As a result, the particles according to Example 1 were composed of 26 mass % Al and the remaining 74 mass % Zn.

[0073] <Examples 2 and 3> Microcapsules for a thermal storage latent heat material were produced under the same conditions as in Example 1. However, the holding temperatures during the oxidation treatment were set to 800° C. and 600° C. Also, similar to Example 1, various properties were analyzed. The oxidation conditions and results are shown in Tables 1 and 2.

[0074] <Comparative Examples 1 and 2> Microcapsules for a thermal storage latent heat material were produced under the same conditions as in Example 1. However, the holding temperatures during the oxidation treatment were set to 900° C. and 1000° C. Also, similar to Example 1, various properties were analyzed. The oxidation conditions and results are shown in Tables 1 and 2.

[0075] In Examples 1 to 3, the shell was thick and the degree of decrease in latent heat was small. In Comparative Example 1, although the shell thickness was ensured, particles adhered to each other, and the powder or microcapsule structure was not maintained. Therefore, particle size measurement was not possible. Furthermore, durability (rate of decrease in latent heat) when the temperature was repeatedly increased and decreased was inferior to that of the Examples. In Comparative Example 2, all of the Al and Zn in the core portion were oxidized. Furthermore, in Comparative Example 2, the degree of adhesion between particles was higher than in Comparative Example 1, making it impossible to measure not only particle size but also other properties. [Table 1] [Table 2]

Claims

1. A microcapsule for a latent heat storage material, comprising a metal core containing Zn and Al and a shell that contacts and covers the metal core, The shell of the microcapsule contains Al, Zn, and O, The shell has a thickness of 1.0 μm or more. A microcapsule for a latent heat storage material, When the total mass of Al and Zn in the core of the microcapsule is 100 parts by mass, Zn is 60 to 95 parts by mass and Al is 5 to 40 parts by mass. Microcapsules for latent heat storage materials.

2. The microcapsule for a latent heat storage material according to claim 1, wherein the shell has a thickness of more than 2.5 μm.

3. A powder containing a plurality of microcapsules for latent heat storage materials according to claim 1 or 2.

4. The powder according to claim 3, having an average particle size of 20 to 100 μm.

5. The powder according to claim 4, having an average particle size of 30 to 50 μm.

6. A heat storage device comprising the powder according to any one of claims 3 to 5.

7. 7. The heat storage device according to claim 6, which is installed on the outer periphery of an exhaust passage of an automobile.

8. 3. The method for producing microcapsules for latent heat storage materials according to claim 1 or 2, comprising sequentially subjecting the Zn-Al alloy particles to a boehmite treatment and an oxidation treatment, wherein the oxidation treatment comprises heating the particles to a holding temperature at a temperature increase rate of 6°C / min or less, and maintaining the particles at the holding temperature in an oxygen-containing atmosphere, A manufacturing method in which the holding temperature is 550°C to 850°C.

9. The method according to claim 8, wherein the temperature rise rate is 4°C / min or less.

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