JP6703734B2 - Mixed viscous heat storage body and manufacturing method thereof - Google Patents

Description

The present invention relates to a mixed viscous heat storage body and a method for manufacturing the same.

The heat storage is a storage method in which the input/output method is a thermal energy form. Thermal energy is the most used form of energy, and it is thought that the development of technology for storing it will contribute significantly to the effective use of energy as a whole.
In recent years, the importance of heat storage materials has been increasing as the efficiency of energy utilization has been increased due to the effects of expanding power demand, global warming, and the problem of fossil fuel depletion. For example, it is expected to be applied in a wide range of fields such as energy saving and improvement of energy use efficiency by applying it to waste heat from factories, clothing and building materials.
The heat storage method can be roughly classified into three types, that is, a sensible heat storage method, a chemical heat storage method, and a latent heat storage method, depending on the form of heat energy to be stored. The sensible heat storage method is a method of storing heat by utilizing the heat capacity of a heat storage material. The principle of heat storage is simple, there are few technical problems, and water, bricks, concrete, etc. are often used, and it has the advantage of being able to store heat stably in a wide temperature range. Especially for the development of water heat storage technology, various applied researches have been made through the design of air conditioning equipment.
On the other hand, there are problems that the amount of heat storage per unit area is small, a large heat storage tank is required, and heat must be stored at a temperature higher than the operating temperature, resulting in large heat loss.
The chemical heat storage method is a method of storing thermal energy as chemical energy by utilizing a chemical reaction. When heat is released, a reverse reaction occurs and the stored chemical energy is recovered as heat energy. Since the chemical heat storage has a large heat storage density and a small heat loss, it has an advantage that it can store heat at room temperature for a long time. In addition, it is possible to utilize in a wide temperature range by appropriately selecting the reaction system. However, since there are many heterogeneous reaction systems, stability is low, and there is a major problem in constructing a heat storage system that can be sustained for a long period of time.
Latent heat storage is a method of storing heat using latent heat that is generally generated during phase change between a solid and a liquid of a substance. It has the advantages that relatively high heat exchange is possible, the heat storage capacity per unit volume is large, and the apparatus volume and mass can be greatly reduced compared to the sensible heat storage method. The substances used for latent heat storage are roughly classified into organic materials such as paraffin and inorganic hydrate materials, and it is necessary to select an appropriate material according to the temperature range to be used.
As described above, each heat storage system has advantages and disadvantages, and it is important to select a system according to purposes such as usage, place, and budget.

As described above, the latent heat storage has a higher heat storage density than other methods, and is attracting attention because it allows the device to be made compact. Above all, ice heat storage has been developed for cooling. Also, latent heat storage technology has been researched and developed for many applications such as power generation using solar heat, heating and cooling hot water supply, and is expected to have future potential. On the other hand, it is also a technology that has many engineering issues.
FIG. 45 shows a basic conceptual diagram of the latent heat storage method. In the latent heat storage method, in the heat storage process, a heat medium having a temperature T _S supplied from a heat source is caused to flow in contact with the heat storage material to give heat to the heat storage material side to melt the solid phase. At this time, T _S is higher than the melting temperature T ₀ of the latent heat storage material (hereinafter referred to as “PCM”). After melting, it means that heat was stored by the latent heat from the solid phase. The heat release process, the temperature T _{R (<T 0)} cause coagulation by passing a heat medium heat is released from the heat storage material, utilizing heat energy out. By utilizing the above in a cycle, heat can be utilized.
The advantages of latent heat storage are that 1) the heat storage density is large and the heat storage tank volume can be made compact, 2) heat can be taken in and out at a temperature that is almost constant, and 3) the larger the economy, the higher the economy. Be done. On the other hand, the disadvantages are 1) the temperature range is limited, 2) the heat storage material and the heat medium must be separated, and a heat exchange process is required. 3) the heat storage material is problematic in terms of toxicity and environmental safety. There are many things, 4) There are many technical problems, and so on.

The study of using PCM in a heat storage tank was started by Telkes M in 1947. Conventional studies on latent heat storage systems include hydrated crystals of inorganic salts, which have large latent heat of fusion and excellent thermophysical properties as heat storage media, and have excellent storage capacity per unit area, wide melting point range, supercooling and phase. Attention has been focused on basic and applied research on latent heat storage systems that utilize organic substances such as paraffin that are unlikely to cause separation phenomena. For example, Inaba and others use tetradecane as a low-temperature latent heat substance, and the thermal properties of an O/W emulsion containing water as a continuous phase are measured to study the emulsion. As a result, it was clarified that the tetradecane oil droplets in the emulsion cause a supercooling phenomenon. A study by FLTan et al. examined the melting and solidification of various forms of heat storage systems. In order to observe the phase change inside the capsule and the convection phenomenon of the capsule by filling n-octadecane in order to store latent heat, compare it with the experimental result and the analysis result with the CFD (Computational fluid dynamics) program. I went. In addition, Tyagi et al. conducted research on the supercooling behavior of CaCl ₂ .6H ₂ O, which is an inorganic hydration material, and found that the supercooling was reduced by changing the pH.

As mentioned above, a wide range of research has been done from the basic to the applied PCM research. Ideally, PCM should melt and solidify at a constant phase change temperature. However, they actually show irreversible behavior and show their performance degradation. This is a major issue in engineering application of PCM. For example, in the case of salt hydrates, supercooling is a particular problem. Even when cooled, it solidifies at a supercooling temperature which is considerably higher than the temperature at which it originally solidifies. In addition, the metastable region varies depending on impurities and cooling rate, so quantitative evaluation is difficult. As a countermeasure, it is possible to add a nucleating agent, etc., but the nucleating agent also varies depending on the material used and analysis is required. In addition, a phase separation phenomenon occurs in which a solid phase and a liquid phase are separated during use. In addition, the molten salt used for high temperature heat storage is highly corrosive to the container etc. and requires anti-corrosion technology, it is necessary to design to avoid the effect of volume expansion on the structure during phase change, low thermal conductivity, etc. The challenges are.

Sodium sulfate decahydrate (Na ₂ SO ₄ ·10H ₂ O) is a typical inorganic hydrate material and is known as a latent heat storage material. Na ₂ SO ₄ ·10H ₂ O is inexpensive and has a relatively large latent heat amount of about 240 kJ/kg, and many studies have been conducted since the 1940s. Further, since it is harmless to the human body and has a melting point of 32° C., it has the advantage of being easy to use even in a living environment.
Pure Na ₂ SO ₄ ·10H ₂ O has a large degree of supercooling, and phase separation occurs in the process of melting and solidification to form Na ₂ SO ₄ ·7H ₂ O, so the heat storage performance and stability deteriorate. FIG. 1 shows the DSC (differential scanning calorimeter) measurement results of Na ₂ SO ₄ ·10H ₂ O in the temperature range of −40° C. to 80° C. As shown in FIG. 1, a peak due to the endotherm during melting was observed at about 32° C. when the temperature was raised from −40° C. However, on the other hand, when the temperature was lowered from 80° C., the peak due to heat dissipation when the crystal solidified was observed in a state of being divided into three. It is considered that such peak splitting is due to the formation of lower hydrates other than the target decahydrate by phase separation. As described above, the phase separation and the supercooled state lead to a decrease in stability, and it becomes difficult to extract heat at a desired temperature. Thus Na ₂ SO ₄ is newly generated Na 2 _SO 4 · _10H 2 _O and water and the three components are metastable melting heat storage material is not melted to become supercooled state becomes below its melting point in a heterogeneous state Form a meta-stable condition. The latent heat amount linearly increases depending on the amount of Na ₂ SO ₄ ·10H ₂ O produced, and thus reduces the performance of the heat storage system. To address these decreases, nucleating agents are typically added to encourage growth. Further, by adding a thickener or the like to increase the viscosity of the entire system and preventing the precipitated Na ₂ SO ₄ particles from precipitating, an equilibrium state can be maintained and phase separation can be prevented. As described above, the initial latent heat quantity of pure Na ₂ SO ₄ ·10H ₂ O is about 240 kJ/kg. However, it decreases to about 64 kJ/kg after 20 to 40 measurements. In the system containing 9.3 wt% thickener, the initial latent heat amount is reduced to about 85% compared to the pure one, but it is possible to maintain the latent heat amount of 106 kJ/kg even after 200 measurements. There is a report that it shows a stable value after that.

Further, in recent years, as one of the measures for preventing phase separation, a method has been adopted in which the melt is confined in a microstructure so that the melt is solidified in the structure. By confining the melt within the microstructure, the water molecules that are released when the higher hydrated salts form lower hydrated salts on endotherm will be in the vicinity of the hydrated salts. Therefore, the hydrated salt can easily take in this water during heat radiation. The basic principle itself is the same as the phase separation prevention measure by adding a thickener. One of the methods for preventing phase separation utilizing such a microstructure is microencapsulation.

A microcapsule is a capsule whose diameter is in the micrometer range when it is regarded as a sphere. However, if the manufacturing method is the same in principle, those with diameters in the millimeter or nanometer range are also called microcapsules. The role of the microcapsules is to protect the contents called core substances or nuclear substances from the external environment. It also has the function of controlling the rate at which the core substance is released to the outside. Due to such a function, microcapsules are used in a wide range of fields. The manufacturing principle is different from the usual one. To make fine microcapsules, the core material is made into fine particles and dispersed in an appropriate medium, and then the fine particles are covered with a film. In particular, the latter process is called microencapsulation. A large number of encapsulation methods have been reported, and they can be roughly classified into a chemical method utilizing a chemical reaction, a physicochemical method utilizing a physicochemical change, and a physical method mainly utilizing a physical or mechanical operation. Can be classified. In addition, it is necessary to select a microencapsulation method depending on the physicochemical/biochemical properties of the substance to be encapsulated, the physical properties of the wall material used, and what kind of function is expected by encapsulation. The method can be roughly divided into the case of using the deposition of the wall material on the interface of the core substance and the case of forming the coating film by using the reaction at the interface, separately from the above-mentioned method. If the former is the interface deposition method and the latter is the interface reaction method, they can be classified as shown in Table 1. In the present invention, the in-situ polymerization method, which is widely and generally used among the interfacial reaction methods, has been focused on.

The in situ polymerization method is a method in which a monomer or a catalyst is added to one of two immiscible phases to cause a polymerization reaction at the interface to form a uniform film on the surface of the core substance. The principle is shown in FIG. The advantage of this method is that the core substance is not limited to a liquid, and a solid or gas can be used. Synthesis of microcapsules with melamine resin as a membrane substance, capsules with crosslinked polystyrene that gives styrene monomer from the outside of W/O emulsion, and capsules that give styrene monomer from the inside of O/W emulsion and contain isooctane inside Has been reported. In addition to polymers, research has been conducted on the synthesis of inorganic wall microcapsules, and synthetic examples of spherical particles having inorganic walls have been reported. For example, hydrated iron oxide spherical particles, zinc oxide spherical particles, calcium carbonate spherical particles, alkaline earth metal silicate spherical particles, and silica wall spherical particles have been reported.
As described above, the microcapsules can be applied to a wide range of fields with various materials, whether organic or inorganic. It is still used in recording materials, medicines, artificial organs, agricultural materials, display materials, fragrances/cosmetics, foods, etc.

In addition, it is a latent heat storage material that is used as a building material by using a material containing a latent heat storage material such as paraffin and a gelling agent. There is known a latent heat storage material having a phase change temperature within a temperature range between the minimum temperature and the maximum temperature of the outer surface receiving the heat (see Patent Document 1). In this example, there is no disclosure of the compounding ratio of sodium sulfate and the polymer, and sufficient heat storage property is not obtained.

WO2013/176050

In the present invention, the heat storage material-containing capsule particles are synthesized by applying the microcapsule technique to Na ₂ SO ₄ ·10H ₂ O, which is a kind of heat storage material. Inclusion of the heat storage material in the capsule particles can be expected to prevent leakage during melting and reduce phase separation. In addition, we tried to synthesize particles containing heat storage material. Moreover, the influence of the catalyst and the surfactant was examined, and an attempt was made to shorten the synthesis time of 24 hours. After that, the function of the catalyst was considered and the mechanism of particle formation was considered.
In addition, the aim was to improve the heat storage performance by increasing the particle size and increasing the amount of Na ₂ SO ₄ ·10H ₂ O inside the particles. In addition, the method of synthesizing hollow silica nanoparticles was applied to particles containing heat storage material, and polyethylene glycol was dissolved in water, which is the continuous phase of the W/O emulsion, to improve emulsion stability and to synthesize particles on the order of micrometers.
In addition, we aimed to further improve the thermal characteristics by changing the polymer used and synthesizing particles containing heat storage material in the same way and utilizing the difference in the interaction.

In the present invention, in order to utilize latent heat special heat utilizing solid-liquid phase change between substances, it is necessary to synthesize capsule particles in which a heat storage material is included inside the particles. In order to obtain higher heat storage performance, it is ideal that the particles are filled with a heat storage material. In addition, it is expected that the larger the particle size, the more the heat storage performance can be exhibited by minimizing the influence of silica.
It has also been reported that capsule particles can be synthesized by adding a sodium sulfate aqueous solution to a cyclohexane solvent to form a W/O emulsion and coating the surface with silica. However, the influence of the amount of catalyst used and the control of particle size have not been established, and there are many unclear points regarding the influence. In addition, the particle synthesis time is set to 24 hours, which is also a problem for application because it is very long. The particle formation mechanism has not been clarified, so it is necessary to clarify the influence of reaction conditions and the mechanism.
Therefore, in the present invention, the influence of the catalyst and the surfactant was examined, the synthesis time was shortened, and then the action of the catalyst was examined and the particle formation mechanism was examined.
A surfactant is used to stabilize the emulsion. The effect of the difference in particle size of the capsule particles on the thermal characteristics has not been clarified yet. As a result, synthesizing particles having a particle size having desired characteristics is considered to be a very important point for application. Generally, the size of the emulsion diameter affects the surfactant concentration. Therefore, the effect of changing the surfactant concentration on the particle size was investigated, and whether control of the particle system was possible was investigated.
In addition, stabilization of the emulsion is considered to be one of the very important factors in considering particle formation. Therefore, it was considered important to investigate the effect of surfactants on particle formation. Therefore, we investigated the effect of surfactants on encapsulation by changing the surfactant type.
The presence of NH ₄ ^{+ that} acts as a catalyst in the hydrolysis and condensation polymerization reaction of TEOS is important. Therefore, we optimized the catalyst concentration during capsule particle synthesis. The synthesis was performed by adjusting the amount of water in the reaction system in order to investigate the timing of the hydrolysis and condensation polymerization reaction of TEOS. It is also reported that the silica shell coating proceeds near the interface of the emulsion due to electrostatic interaction between the amine catalyst having a cation and the anionic surfactant. Therefore, we investigated the mechanism of catalytic action in the reaction by controlling the electrical interaction of the catalyst in the reaction by changing the pH during the synthesis. Based on the above, an attempt was made to shorten the long reaction time of 24 hours. In order to improve the catalytic activity, 3-3 diaminodipropylamine, which has a total of 3 amino groups at both ends and inside, and ammonia, which is widely used as a catalyst, are used to influence the reaction time and the effect of catalyst species on particle formation. Examined.

INDUSTRIAL APPLICABILITY According to the present invention, a heat storage material corresponding to various shapes such as a bag shape and a box shape can be easily obtained by using a mixed viscous material of a polymer and an inorganic salt. The viscosity can be adjusted by the blending ratio of the polymer and the inorganic salt. It can also be used as a powder by encapsulation. Since the heat storage property is obtained even when it is made into a nano size, it is possible to impart visible light transparency and knead into a coating material or a film.

FIG. 1 is a graph showing the DSC measurement results of Na ₂ SO ₄ ·10H ₂ O according to the present invention. FIG. 2 is a principle diagram of microencapsulation by a polymerization method. FIG. 3 is a flow chart of capsule particle synthesis when the surfactant is changed. FIG. 4 is a flowchart showing a particle synthesis procedure in which the catalyst species are changed. FIG. 5 is an SEM image in the TED mode. FIG. 6 is a graph showing the DSC measurement results at various surfactant concentrations. FIG. 7 is an SEM image showing particles when different kinds of surfactants are used. FIG. 8 is a graph showing the DSC measurement results of Span80. FIG. 9 is an SEM image showing particles when the amount of water was adjusted. FIG. 10 is a graph showing the DSC measurement results of synthetic particles in a water amount control system and a normal system. FIG. 11 is an SEM image showing particles synthesized with NH ₃ as a catalyst and a reaction time of 12 hours. FIG. 12 is an SEM image showing particles synthesized under the conditions of 3-3′ diaminodipropylamine catalyst, reaction time (a) of 6 hours, and (b) of 12 hours. FIG. 13 is a graph showing the relationship between shear rate and viscosity when using each catalyst. FIG. 14: is a flowchart which shows the procedure at the time of synthesize|combining by changing the aqueous solution concentration of the sodium sulfate decahydrate used as a heat storage material. FIG. 15 is a flow chart showing the procedure of synthesis without adding a polymer in the aqueous phase. FIG. 16 is a flowchart showing a procedure for synthesizing PEG by changing its molecular weight and concentration. FIG. 17 is an SEM image showing particles synthesized by changing the sodium sulfate aqueous solution concentration. FIG. 18 is a graph showing XRD (X-ray analysis) results. FIG. 19 is a graph showing the results of DSC (differential scanning calorimetry). FIG. 20 is a graph showing the results of repeated measurement of particles synthesized under the condition of sodium sulfate 10%. FIG. 21 is a graph showing the relationship between the amount of heat absorption and the number of cycles obtained from repeated measurements. FIG. 22 is an SEM image in the state where no PEG was added. FIG. 23 is a conceptual diagram showing an image of additive-free silica shell formation. FIG. 24 is a graph showing a DSC measurement comparison under the presence or absence of a polymer. FIG. 25 is an SEM image showing particles synthesized under the condition of changing the PEG concentration. FIG. 26 is an EDS image showing particles, where (a) is 3.0 wt %, (b) is 7.5 wt %, and (c) is 9.0 wt %. FIG. 27 is a graph showing the results of Raman spectroscopy measurement. FIG. 28 is a graph showing the results of TG measurement of PEG-Na ₂ SO ₄ . FIG. 29 is a graph showing the DSC measurement results of particles. FIG. 30 is a conceptual diagram showing an image of sodium sulfate uptake according to PEG concentration. FIG. 31 is a structural formula of a polymer. FIG. 32 is a flow chart showing the synthesis procedure under the condition that the polymer is changed. FIG. 33 is an SEM and EDS image of synthetic particles under PAA conditions. FIG. 34 is an SEM and EDS image of synthetic particles according to PEI conditions. FIG. 35 is an SEM and EDS image of synthetic particles under PVA conditions. FIG. 36 is an SEM and EDS image of synthetic particles under PVP conditions. FIG. 37 is a graph showing the XRD measurement result of each sample. FIG. 38 is a graph showing the DSC measurement result of each synthesized particle. FIG. 39 is a graph showing the relationship between the shear rate and the viscosity of a polymer aqueous solution and a polymer/sodium sulfate aqueous solution. FIG. 40 is a graph showing the relationship between the shear rate and the viscosity of the polymer aqueous solution excluding PVA and the polymer/sodium sulfate aqueous solution. FIG. 41 is a graph showing the relationship of the temporal change of emulsion diameter under PEI conditions. FIG. 42 is a graph showing the relationship of the temporal change of emulsion diameter under PVA conditions. FIG. 43 is a graph showing the relationship of the temporal change in emulsion diameter under PVP conditions. FIG. 44 is a conceptual diagram showing a PVP behavior image. FIG. 45 is a basic conceptual diagram showing the latent heat storage method.

For the purpose of inexpensively providing heat storage microcapsules that can be used as powder and have visible light transparency, an aqueous polymer solution, a polymer/sodium sulfate aqueous solution and a water-soluble surfactant are used as an aqueous phase, and octanol and a thickener are used. It was realized by using and as an oil phase and dropping an inorganic salt.

〔material〕
As the core PCM (latent heat storage material), sodium sulfate decahydrate (Wako Pure Chemical Industries, Ltd.) was used. Cyclohexane (Wako Pure Chemical Industries, Ltd.) as a solvent, sodium dodecyl sulfate (Wako Pure Chemical Industries, Ltd.), sorbitan monooleate (Span 80) (Tokyo Chemical Industry Co., Ltd.)) as a surfactant for forming an emulsion), t-octyl Phenoxypolyethoxyethanol (Triton X-100) (Nacalai Tesque) was used. Tetraethyl orthosilicate (TEOS) (Wako Pure Chemical Industries, Ltd.) was used as the silica precursor that became the shell of the particles, and 3-aminopropyltriethoxysilane (APTS) (Shin-Etsu Silicone) was used as the catalyst.

〔Production method〕
A manufacturing flow chart is shown in FIG. Table 2 shows the composition of the reagents used at that time.

Cyclohexane was added to a 50 mL beaker and stirred with heating with a hot stirrer at 60°C. Then, SDS was added to 0.02M and the solution was stirred until it became slightly cloudy. Then, a 2M Na ₂ SO ₄ aqueous solution was added at once and 1-pentanol was also added at once to form an emulsion. After stirring for 15 minutes, the mixture was aged for 1 hour, TEOS was added dropwise with stirring again, APTS was added, and the mixture was reacted for 24 hours. After completion of the reaction, centrifugation was performed and washing with ethanol was performed three times. After washing, it was dried overnight at 10° C. to obtain particles. Although there was no clear description in the report of the amount of APTS as a catalyst, in this example, as shown in Table 2, a predetermined amount of 2 wt% APTS aqueous solution was added. Similarly, the effect of particle formation was investigated by changing the surfactant species. The procedure was the same as in FIG. Table 3 shows the amount of reagents at the time of synthesis. The amount of surfactant was added so as to have the same concentration according to the system of SDS 0.02M.

Table 4 shows the amounts of reagents when the catalyst concentration was changed and synthesis was performed. The synthesis procedure was the same as that shown in FIG.

In order to study the mechanism, the amount of water in the whole system was adjusted and the synthesis was performed. The synthesis procedure was the same as that shown in FIG. Table 6 shows the amounts of reagents at the time of synthesis.
Further, FIG. 4 shows the synthetic procedure when the kind of the catalyst is changed, and Table 5 shows the reagent amount at the time of synthesis.

[Evaluation]
a. SEM
An observation sample was prepared by dispersing the dried particles in ethanol and dropping them on a microgrid. Then, osmium was vapor-deposited with OSMIUM PLASMA COATER OPC60A (Filgen). For the observation, a scanning electron microscope (JSM-7000F, manufactured by JEOL) was used, and the acceleration voltage was 15.0 kV. Secondary Electron Image (SEI) and Transmission Electron Diffraction (TED) modes were used for observation.
b. XRD measurement An X-ray diffraction pattern was measured using an X-ray diffractometer (RINT1000, manufactured by Rigaku) in order to confirm the crystal structure of sodium sulfate. The applied voltage was 40 kV, the applied current was 40 mV, the measurement range was 10 to 70 degrees, and the attachment rotation speed was 60 rpm.
c. A differential scanning calorimeter (Thermo Plus DSC8230, manufactured by Rigak) was used to evaluate the thermal characteristics of the DSC measurement particles. The measurement was carried out under the conditions of the endothermic and exothermic measurement ranges of -40°C to 80°C, the number of cycles of 3 and the rate of temperature increase/decrease of 40°C/min. Further, the measurement was started from a state of being initially cooled to -40°C, lowered to 80°C, and then cooled again to -40°C. The results show the results of the third measurement unless otherwise specified.
d. Viscosity Measurement The viscosity of the mixed solution when the catalyst species was changed was measured under the following conditions using a rotary viscometer (HAAKE Rheo Stress 6000 manufactured by Thermo Fisher Scientific). (Shear speed 200 to 800 m/s, measurement time 60 s, cone c20/Ti)
e. pH measurement
The pH of the solution was measured using a pH meter (METTLER TOLEDO, SevenGo pH meter SG2) under the condition that the APTS concentration was changed.

〔Results and discussion〕
In order to investigate the effect of the particle size due to the difference in the surfactant concentration, the amount of APTS was fixed at 0.70 mL, and the effect on the particle size and morphology when the concentration of SDS as the surfactant was changed was examined. The activator concentration was adjusted to 0.005 to 0.04 M as shown in Table 3 and added.
Fig. 5 shows SEM images of particles synthesized by changing the surfactant concentration. Further, it was found that spherical particles of about 50 to 80 nm were synthesized in (a) and (b). In (c), a state in which fine particles were aggregated was observed. No particles were obtained under the condition that the SDS concentration was 0.005M.
At 0.005M, the surfactant was in a dilute state and did not reach the critical micelle concentration (cmc), which is the minimum concentration required to form micelles, and therefore it is considered that no emulsion was formed and no particles were synthesized. Further, it can be seen from FIG. 5 that the particle size decreases as the surfactant concentration increases. When the concentration is high, micelles are easily formed because the amount of the surfactant present in the solution is large. Therefore, it can be considered that even in an emulsion having a small diameter, it can exist more stably than in a system having a low concentration, and the particle diameter is also reduced.

Figure 6 shows the DSC measurement results. A peak due to melting of sodium sulfate decahydrate was observed around 30° C. at any concentration. It was observed that the freezing point tended to increase with increasing SDS concentration. The increase in freezing point was in the range of about -10°C to 10°C.
From the results of SEM and DSC, it was found that the particle size tends to decrease as the SDS concentration increases. An increase in the freezing point was observed as the particle size decreased. It is considered that crystallization was facilitated because the internal pressure increased as the particle size decreased. It is known from the Young-Laplace equation (Equation 1) that the internal pressure increases in inverse proportion to the particle size. Here, ΔP is the difference between the internal pressure Pi and the external pressure Pg, γ is the surface tension, and r is the particle radius. According to (Equation 1), the smaller the particle size, the larger the internal pressure and the more unstable the internal state. Therefore, it is considered that crystallization is easy even in a high temperature range. As a result, it is considered that the freezing point increased as the particle size decreased. In addition, since silica is present as an external factor in the surroundings, there is a possibility that some nuclei exist and the nucleation is facilitated as compared with the case of the raw material.

Different surfactant species were prepared to investigate the effect of surfactant on emulsion stabilization and particle formation.
FIG. 7 shows an SEM image of particles synthesized using Span 80 or Triton X-100 as a surfactant. In the system using Span 80, spherical particles of about 180 nm were observed.
The TED results also showed that the inside of the particles was partially hollow, and a substance thought to be sodium sulfate was confirmed, suggesting that the particles were encapsulated in the same manner as under the conditions using SDS. On the other hand, on the other hand, in the system synthesized using Triton X-100, spherical particles of about 100 to 200 nm can be observed, but it can be seen from the results of TED that the particles are solid particles. Therefore, it was found that the encapsulated particles could not be synthesized. FIG. 8 shows the result of DSC measurement. In the system using Span 80, a peak due to melting can be confirmed at around 30°C when the temperature is raised, and a peak due to solidification can be confirmed at around 0°C when the temperature is lowered. From the above results, it was found that capsule particles can be synthesized in the system using Span80.
The difference in particle formation due to the difference in the surfactant is explained by the HLB value of the surfactant. The HLB value is a value representing the balance between the lipophilicity and the hydrophilicity of the surfactant and can be calculated by the Griffin method (Equation 2).

According to Formula 2, a substance having more hydrophilic groups with respect to hydrophobic groups has a higher HLB value, and a substance having more hydrophobic groups has a lower HLB value. Therefore, it is generally said that a surfactant having a high HLB value contributes to the stability of an O/W emulsion, and an surfactant having a low HLB value contributes to the stability of a W/O emulsion. Table 7 shows the HLB values of the surfactants used this time. Table 7 shows that Span 80 has a low HLB value and high lipophilicity. Therefore, it is considered that the formation of particles was facilitated by contributing to the stabilization of the W/O emulsion. Since Triton X-100 has a high HLB value of 13.5, it has high hydrophilicity and the emulsion was unstable and collapsed, and it is considered that solid particles were formed.

Particles were synthesized by changing the amount of APTS aqueous solution added to 0.35, 0.70, 1.4, 2.1, and 4.2 mL, and the influence of the catalyst concentration on the particle diameter and morphology was investigated.
Fig. 5 shows SEM images of particles synthesized at each concentration. FIG. 6 shows the XRD measurement result of the obtained particles, and FIG. 7 shows the result of thermal property evaluation by DSC.
From FIG. 5, spherical particles of about 50 to 100 nm were confirmed under the conditions except 4.2 mL. In addition, there was no difference in the particle shape depending on the amount of APTS added, and no consistent tendency was observed in the particle size depending on the amount of APTS added. On the other hand, particles could not be confirmed in the system in which 4.2 mL was added and the catalyst concentration was high. It is considered that this is because the amount of water, which is a solvent, increases as the amount of the catalyst increases, so that the viscosity of the entire system decreases and the emulsion becomes unstable. Under the conditions where particles could be confirmed, TED was observed with the central part of the particles being transmitted. It is considered that this is because Na ₂ SO ₄ inside was partially dissolved by its own water of crystallization, and was observed as a hollow state. There are some particles such as particles synthesized under the condition of 1.4 mL in which some shadows can be observed. It is considered that Na ₂ SO ₄ remained inside without being melted in water of crystallization.
From the XRD measurement results, no change in peak was observed depending on the catalyst concentration. From this, it is considered that the catalyst concentration does not influence the formation of Na ₂ SO ₄ .10H ₂ O inside.
Peaks due to heat absorption and heat dissipation were observed in all the particles obtained by the DSC measurement in FIG. 7. It can also be seen that the heat release peak during solidification decreases with the increase in APTS. As APTS increases, the amount of APTS that does not contribute to particle shell formation also increases. APTS acts as a base catalyst for TEOS. Therefore, it is expected that TEOS will undergo hydrolysis and condensation polymerization reactions other than on the core surface, increasing the amount of solid particles not having PCM as the core. As a result, it is considered that the amount of heat decreased relatively.

It was confirmed that particles can be synthesized under various conditions by changing the surfactant species and the amount of catalyst. Here, the formation mechanism of the latent heat storage material-containing particles will be described in detail. In this example, silica is coated using the hydrolysis reaction of TEOS. At that time, it was investigated at what timing the hydrolysis occurred and the reaction proceeded. In this example, it was investigated whether the water in the APTS aqueous solution contributed to the reaction or the water in the water phase used for emulsion formation contributed by adding the APTS raw material as it was, instead of the APTS aqueous solution.
FIG. 9 shows an SEM image of the synthesized particles. From the SEM observation, only a few solid particles were observed. The particle size was about 80 to 100 nm, and the shape was spherical. The amount of particles observed was also small. FIG. 10 shows a comparison result of DSC measurement between the particles synthesized this time and the particles synthesized by adding 0.70 mL of an APTS aqueous solution. In the DSC measurement, the endothermic peak due to the melting of sodium sulfate decahydrate around 32° C. observed at the time of temperature rise could not be observed. In addition, a small broad peak can be confirmed near 0°C. This is considered to be a peak that appeared because residual water that could not be completely removed during drying solidified. Thus, it was confirmed that the particles obtained under the conditions of this time do not exhibit thermal characteristics. From the above results, it can be inferred that the hydrolysis-condensation polymerization reaction of TEOS mainly proceeds using water in the APTS aqueous solution as a reaction source. Therefore, it is considered that in the system using the APTS raw material, the reaction did not proceed sufficiently and the amount of particles decreased.

Table 8 shows a summary of the pH when 0.70 mL of APTS aqueous solution of each concentration was added to the emulsion form solution. In the column of particle formation, “O” indicates that capsule particles were confirmed, and “X” indicates that neither capsule particles nor solid particles could be confirmed. The case where only solid particles were observed was marked with Δ. From the results in Table 8, it can be seen that no particles were formed when the APTS concentration was 1 wt% or less. Further, it was found that when the APTS concentration was 6 wt% or more, the solid particles were formed although the particles were formed but the capsule particles were not formed. APTS and SDS are believed to react at the emulsion interface due to their electrostatic interaction. Hydrophilic groups in the SDS having a negative charge as amino propyl positive charge (-NH 3 ^₊₎ present in the APTS (-SO 3 ^_-) is present near the interface APTS easily react by interaction is thought to proceed. Under the condition where the APTS concentration is low, the pH of the solvent is low and the value is almost neutral. Therefore, it is considered that APTS did not act sufficiently as a catalyst and TEOS hydrolysis and condensation polymerization reaction did not proceed. In addition, the pH becomes high under the condition of high APTS concentration. The pKa of the aminopropyl group shows a value of about 10.6 at room temperature, and the dissociation equilibrium of the aminopropyl group tends to the nonionic type when the pH becomes 10.6 or higher. Therefore, at high pH, the aminopropyl group becomes charge-neutral and the electrostatic interaction with SDS is weakened. It is considered that solid particles were observed instead of capsule particles because APTS did not collect at the emulsion interface and diffused throughout the solution due to weakened electrostatic interaction. Tatsumi et al. have reported the synthesis conditions of mesoporous silica by using ethanol as a continuous phase, water as a disperse phase, SDS as a surfactant, pH of 2 to 13 and adding APTS and TEOS. According to this report, hydrolysis does not proceed under conditions where the pH is 8 or less, and it is difficult to form silica when the pH is 11 or more due to the decreased interaction as described above.

In order to shorten the synthesis time of 24 hours, we focused on the catalyst to be added and synthesized it using 3-3 diaminodipropylamine, which has many NH ₃ and amino groups that are generally used as TEOS catalysts. Was investigated.
SEM images of the particles synthesized under the condition of (a) 12 hours by adding NH ₃ in FIG. 11, and in FIG. 12 by adding 3-3′diaminodipropylamine (a) for 6 hours and (b) for 12 hours. The SEM image of the particle synthesize|combined on condition is shown. In the system in which NH ₃ was added, no product was observed at a stirring time of 6 hours. From FIG. 9, solid particles were observed when the stirring time was 12 hours. In the system to which 3-3'diaminodipropylamine was added, a state in which the capsule particles partially aggregated was observed at both 6 and 12 hours.
FIG. 13 shows the relationship between the shear rate and the viscosity of each emulsion solution. Since 3-3'diaminodipropylamine has amino groups at both ends and inside, it is considered that the pH is increased and the hydrolysis and condensation polymerization reaction of TEOS are further promoted. Further, in NH ₃ , the amount of water in the entire system increases and the viscosity decreases, whereas 3-3′diaminodipropylamine has a large viscosity itself, and therefore it is considered that the viscosity increases even when an aqueous solution is added. As a result, it is considered that the emulsion was stabilized and silica was likely to be deposited on the surface, and the particles could be formed even in a short reaction time.

We succeeded in synthesizing capsule particles by adding a sodium sulfate aqueous solution in a cyclohexane solvent to form a W/O emulsion and coating the surface with silica. It was revealed that the surfactant concentration mainly affects the particle size in the particle formation process. In addition, since the freezing point of PCM inside changes with the change of particle size, it is suggested that the freezing point can be controlled by controlling the particle size. Further, it has been clarified that it is necessary to select an appropriate surfactant because the contribution to the stability of the W/O emulsion varies depending on the difference in HLB value of the surfactant. Regarding the reaction time required for particle formation, 18 hours was successfully shortened by using 3-3'diaminodipropylamine as a catalyst. At that time, it was suggested that the amino group (catalytic ability) of the catalyst and the viscosity are important factors.

[Synthesis of capsule particles]
In this example, a synthesis method using cyclohexane as a solvent and an aqueous sodium sulfate solution as a core was used. It was revealed that it is possible to reduce the synthesis time by 16 hours by controlling the particle size obtained by changing the surfactant concentration on the order of several tens of nm and further devising a catalyst to be used. However, although it is possible to control the particle size on the order of several tens of nm, larger particles are needed than when aiming at further improvement in heat storage performance. According to the method reported by Zhao et al., it is considered that it is difficult to stably form a larger emulsion because the emulsion is relatively unstable because the aqueous phase is only the sodium sulfate aqueous solution. In order to improve the heat storage performance, it is necessary to design particles such that sodium sulfate is more densely incorporated into the inside even if the particle diameter is the same, or the particle diameter is increased to increase the amount of incorporation. In this example, an attempt was made to improve the heat storage performance by designing the latter by increasing the particle size and increasing the amount of contained sodium sulfate. Seong-Geuh Oh et al. reported the synthesis of spherical hollow silica particles of 3 to 6 μm in which the stability of the emulsion was improved by dissolving a polymer such as polyethylene glycol in water as a dispersed phase. Therefore, we tried to dissolve polyethylene glycol, which is a water-soluble polymer, in the aqueous phase, adjust the viscosity of the aqueous solution, stabilize the emulsion, and increase the particle size. As a result, the size of the particles themselves can be increased and the heat storage performance can be expected to improve. In addition, we investigated the conditions under which particles can be synthesized by fixing the polymer concentration and changing the concentration of sodium sulfate added to the aqueous phase. In order to confirm the effect of the polymer in the aqueous solution as the core and the effect on the stability of the emulsion, the particles were synthesized without adding the polymer to the aqueous phase, and the effect on the particle formation by the presence or absence of the polymer was considered. did. Further, by fixing the sodium sulfate aqueous solution concentration to 50 wt% and changing the polymer concentration, the effect of the interaction between the polymer and sodium sulfate on the improvement of the inclusion amount of sodium sulfate inside the particles and the influence on the particle formation were examined. ..

〔material〕
Polyethylene glycol (PEG) (degree of polymerization 20000, Wako Pure Chemical Industries, Ltd.), 25% ammonia water (Wako Pure Chemical Industries, Ltd.), and sodium sulfate decahydrate (Wako Pure Chemical Industries, Ltd.) were used for core formation. In addition, polyoxyethylene sorbitan monolaurate (Tween 20) as a water-soluble surfactant, 1-octanol (Wako Pure Chemical Industries, Ltd.) as an oil phase, hydroxypropyl cellulose (HPC) as a thickener (Wako Pure Chemical Industries, Ltd.) As the oil-soluble surfactant, sorbitan monooleate (Span 80) (Tokyo Chemical Industry Co., Ltd.) was used. Tetraethyl orthosilicate (TEOS) (Wako Pure Chemical Industries, Ltd.) was used as a silica precursor.

〔Production method〕
It has been reported that a polymer is dissolved in water as a dispersed phase to enhance the stability of the emulsion and to synthesize spherical hollow silica particles of 3 to 6 μm.
HPC was added to octanol, and the mixture was stirred and dissolved at 80° C. for 4 hours using a hot stirrer, dissolved, cooled to room temperature, Span 80 was added, and the mixture was stirred at 40° C. In another container, PEG was added and dissolved in water, Tween 20 was added, and the mixture was stirred for 20 minutes. Then, aqueous ammonia was added to form an aqueous phase. This aqueous phase solution was added dropwise to the oil phase stirred at 40° C. so that the volume ratio of aqueous phase:oil phase was 1:9. After stirring for 30 minutes, TEOS was added dropwise at 30 μL/min using an automatic dropping device.
The particles were synthesized by stirring for 14 hours. After completion of the reaction, centrifugation was performed and washing with ethanol was performed three times. Sodium sulphate decahydrate becomes volatile when left in air at room temperature. Therefore, after washing, it was dried overnight at 10° C. to obtain particles. FIG. 14 shows a procedure for synthesizing sodium sulfate decahydrate used as a heat storage material by changing the aqueous solution concentration. An aqueous solution of sodium sulfate as a heat storage material was added so as to be 10, 50, 100 wt% with respect to the aqueous phase. Table 9 shows the composition of the reagents used in the oil phase and the water phase. FIG. 15 shows the procedure of synthesis without adding a polymer in the aqueous phase. Table 9 shows the composition of the reagents used. FIG. 16 shows the procedure for synthesizing PEG by changing its molecular weight and concentration. Table 10 shows the changed composition.

[Evaluation]
a. SEM
An observation sample was prepared by fixing the dried particles to a brass sample stand to which a carbon tape was attached. Then, osmium was vapor-deposited by OSMIUM PLASMA COATER OPC60A (Filgen). For the observation, a scanning electron microscope (JSM-7000F, manufactured by JEOL) was used, and the acceleration voltage was 15.0 kV. Secondary Electron Image (SEI) mode was used for observation.
b. XRD measurement An X-ray diffraction pattern was measured using an X-ray diffractometer (RINT1000, manufactured by Rigaku) in order to confirm the crystal structure of sodium sulfate. The applied voltage was 40 kV, the applied current was 40 mV, the measurement range was 10 to 70 degrees, and the attachment rotation speed was 60 rpm.
c. A differential scanning calorimeter (Thermo Plus DSC8230, manufactured by Rigak) was used to evaluate the thermal characteristics of the DSC measurement particles. The measurement was performed under the conditions of measurement range of endotherm and calorific value of −40° C. to 80° C., three cycles, and temperature rising/falling rate 10° C./min. Further, the measurement was started from a state of being initially cooled to -40°C, and after being heated to 80°C, it was cooled to -40°C again. The results show the results of the third measurement unless otherwise specified.
d. Raman spectroscopy The Raman spectrum was measured using a laser Raman spectrophotometer (NRS-3100 manufactured by JASCO Corporation) in order to confirm the presence of sodium sulfate decahydrate in the produced particles. A lens having a magnification of 100 times was used as an objective lens, a green laser beam having a wavelength of 532.0 nm was used as an excitation laser, an exposure time was 5 seconds, a laser output was 4 to 6 W, and the number of integration was 16 times.
e. TG measurement In order to quantify the amount of sodium sulfate encapsulated in the polymer, PEG dissolved in an appropriate amount of hexane and the dissolved sodium sulfate incorporated therein were precipitated in an aqueous emulsion solution. The sample was then dried overnight at 10°C. After drying, the sample was heated at 10° C./min to 1000° C., and TG measurement was performed.

〔Results and discussion〕
FIG. 17 shows SEM images of particles produced under the conditions of the sodium sulfate aqueous solution amount of 10, 50, and 100 wt %. As a result of observation by SEM, particles could be observed only in the system in which 10% was added. The particles observed were spherical particles having a particle size of about 3 μm, and the surface was smooth. In addition, nothing other than spherical particles was observed. In the 50% system, it was observed that the microparticles formed spherical micelles and collapsed. In addition, a product having a size of several μm was confirmed outside (arrow portion). It is considered sodium sulfate. Therefore, it is considered that the silica shell and sodium sulfate are separately generated. In the 100% system, spherical particles as observed in the 10% system were not observed, and a product of several μm as observed in the 50% system was observed. FIG. 18 shows the XRD (X-ray analysis) measurement result. A peak of sodium sulfate was observed in all samples by XRD measurement. It was suggested that sodium sulfate was encapsulated inside under the condition of 10 wt %. It is considered that under the conditions of 50 and 100 wt %, particles of sodium sulfate were not formed and the sodium sulfate precipitated outside was detected. Further, a broad peak was observed from 20 to 30 degrees, which shows that amorphous silica was produced. At 10%, the peaks due to sodium sulfate are reduced compared to the other concentrations. This is considered to be because the concentration of sodium sulfate was relatively low and the peak was decreased because the formation of silica particles was confirmed as compared with other systems.
FIG. 19 shows the DSC (differential scanning calorimetry) results of the prepared sample. In the 10% sample, melting and melting peaks of sodium sulfate at around 50° C. and absorption and heat radiation peaks at around 38° C. due to solidification were observed. On the other hand, no peak was observed in the 50 and 100% systems.

FIG. 20 shows the results of repeated measurement of particles synthesized under the condition of 10% sodium sulfate. Further, FIG. 21 shows the relationship between the amount of heat absorption and the number of cycles obtained from repeated measurements. It was found from FIG. 20 that no large change was observed in the amount of stored heat even when continuous measurement was performed. Further, the peak positions are slightly shifted in the first cycle and the second cycle and thereafter. Initially, sodium sulfate crystals were randomly deposited inside the particles, and it is considered that crystallization is incomplete. However, it is considered that the peak shift does not occur from the second time onward because the crystalline state inside the particles is aligned and stabilized by repeating melting and solidification. From FIG. 21, the heat absorption amount is almost stable even if the cycle is repeated. From this, it was found that PCM-encapsulating capsule particles exhibiting stable thermal characteristics can be synthesized under the condition of sodium nitrite sulfate concentration of 10%.

In order to examine whether or not PEG has an effect on particle synthesis and heat storage performance, the effect was examined in a polymer-free system. FIG. 22 shows an SEM image. From the observation with SEM, particles in which the shell of several μm to 10 μm collapsed were observed. As shown in FIG. 22, it was observed that the particle formation did not proceed completely and the silica coating had some holes. It is considered that the viscosity in the aqueous phase is low when the core PEG is not added. Therefore, the emulsion interface is very unstable in the PEG-free state, and it is considered that the state is as shown in FIG. In the state where the viscosity is large and the emulsion is stable, the solvent that diffuses in water as shown in FIG. 23-A can exist stably even at the interface. However, under the PEG-free condition, the viscosity was small and the interface was unstable as compared with the adding condition, and as shown in FIG. Therefore, it is considered that even if the reaction with TEOS proceeded and a silica shell was formed, it did not cover the entire emulsion, and pores were created and the shell collapsed. From this, it is considered that the coating with silica was difficult and the state as shown in FIG. 22 was observed as compared with the system to which PEG was added.
FIG. 24 shows a comparison in DSC measurement of the sample synthesized without adding PEG and the particles synthesized under the condition of 10% aqueous sodium sulfate solution synthesized. As can be seen from FIG. 24, no endothermic peak could be confirmed under the PEG-free condition. This is in agreement with the observation result by SEM, and it can be seen that Na ₂ SO ₄ does not exist under the condition that PEG is not added. From the above results, it can be said that the polymer dissolved in the aqueous phase plays an important role as a core during particle formation and is one of the indispensable factors for the formation of capsule particles.

As described above, it was revealed that the heat storage material-containing particles can be synthesized under the condition of the sodium sulfate aqueous solution of 10 wt %. However, in order to further improve the heat storage performance, it is necessary to take measures such as increasing the amount of sodium sulfate inside. Therefore, an attempt was made to increase the amount of sodium sulfate taken into the particles by increasing the PEG concentration by setting the sodium sulfate aqueous solution concentration to 50 wt %. FIG. 25 shows SEM images of particles synthesized by changing the PEG concentration added to 3.0, 6.0, 7.5, and 9.0 wt% in a system using a molecular weight of PEG of 20000. At a PEG concentration of 6.0 wt %, it was observed that particles could not be completely formed. This behavior was not observed at other concentrations. At 6 wt %, it is considered that the core did not have sufficient stability, silica particles were hard to deposit on the core surface, and the particles could not be completely formed within the reaction time of 14 hours. At other concentrations, particles were observed and there was no difference in their particle size.
FIG. 26 shows EDS images of particles synthesized under the conditions of 3.0, 7.5 and 9.0 wt %. From this, it was found that the particles were silica particles. Similarly, since the mapping of Na can be confirmed on the silica particles, it is considered that sodium sulfate is present inside, and it is suggested that the particles may be capsule particles. However, it is difficult to conclude whether the sodium sulfate exists outside or inside the particle, and it cannot be concluded from the EDS results alone. 27 shows the result of Raman spectroscopy measurement. It is known that a peak attributed to the all-symmetric stretching vibration of sulfate ion appears near 990 cm ⁻¹ in Raman spectroscopy measurement with sodium sulfate. From the measurement results, a peak derived from the vibration of sulfate ion was observed at any concentration, and it was found that sodium sulfate was present in the sample. A peak was similarly observed in the 6 wt% system in which the presence of particles was not confirmed by observation with SEM or the like. It is considered that the sodium sulfate deposited outside was not completely removed by the washing operation and remained in the sample. Further, the respective peak intensities became strong in the order of 7.5 wt>6 wt≧9 wt>3 wt. The intensity parameter I, which defines the peak intensity in the Raman spectrum, is represented by (Equation 3).

Where I ₀ is the incident laser light intensity, T(ν) is the transmittance of the spectroscope, ν is the scattered light frequency, A(ν) is the absorption intensity by the sample, and α(ν) is the Kramers-Heisenberg-Dirac The polarizability expressed by the dispersion formula, and c is the sample concentration. Since I ₀ , T(ν), ν, and A(ν) are constant values depending on the sample, I is proportional to the sample concentration c. Therefore, it is generally considered possible to quantitatively evaluate sodium sulfate in particles using Raman spectroscopy. However, in this example, the Raman spectrum intensity was measured high under the condition of 6.0 wt% in which particles were not formed. The spectral intensity is expected to decrease under the condition that no particles are originally formed. As described above, the Raman spectrum intensity depends on the concentration of the measurement sample. In the 6.0 wt% sample in which particles are not formed, it is considered that the amount of silica present in the sample is smaller than that in the system in which particles can be confirmed. Therefore, it is considered that the amount of sodium sulfate in the sample was relatively large and the strength was observed as described above.

Hexane was added to the emulsion solution, and PEG was deposited while sodium sulfate was included inside. FIG. 28 shows the result of TG measurement of the sample obtained here. The purpose of this example is to quantify the difference in the amount of sodium sulfate incorporated inside the particles due to the difference in PEG concentration. From FIG. 28, at any concentration, the weight reduction started near 300° C. and the weight became almost constant near 400° C. Therefore, it is considered that the thermal decomposition of PEG started at around 300°C and was completely decomposed at about 400°C. This result shows how much sodium sulfate is incorporated with respect to the weight of PEG. Under the conditions of PEG 7.5 and 3.0 wt %, the weight reduction rates are almost the same as 57.1 and 58.2%, respectively. Further, it was 88.7% at 9 wt% and 93.7% at 6.0 wt%. From this, it was suggested that even at 6 wt% where particle formation could not be confirmed, a small amount of sodium sulfate was incorporated inside the emulsion form.
FIG. 29 shows the DSC measurement result of particles excluding 6.0 wt %. From FIG. 29, it was possible to confirm the peak due to heat absorption and heat dissipation in all the measured samples. The amount of heat absorption and heat release was correlated with the result shown in FIG. 28, and particles having a larger amount of sodium sulfate incorporated therein showed higher heat storage properties. That is, under the conditions of PEG 7.5 and 3.0 wt %, there was no difference in the amount taken into the interior and no significant difference was found in the amount of heat storage. At 9.0 wt %, the amount of incorporation into the inside is small and the amount of heat storage is greatly reduced compared to the other concentration conditions. From the above results, it was clarified that the amount of sodium sulfate, which is a heat storage material, taken in was different depending on the difference in PEG concentration used in the aqueous phase.

It is believed that increasing the concentration of PEG increases its interaction with sodium sulfate. Therefore, it is considered that the sodium sulphate incorporated increases as the internal PEG increases. However, the result of this example shows that the heat storage performance is higher under the condition of low concentration of 3 wt% than that of high concentration of 9 wt %. The volume ratio of PEG inside the particles increases as the PEG concentration increases. Therefore, it is expected that sodium sulfate will be difficult to be taken into the inside, while the interaction becomes stronger. Therefore, it is considered that the amount of sodium sulfate taken in by the presence of PEG at a certain concentration or more decreased, and the heat storage performance seemed to deteriorate (see FIG. 30).

By dissolving a water-soluble polymer in the aqueous phase, increasing the viscosity of the aqueous solution, and using the dissolved polymer as a kind of core, we succeeded in synthesizing particles having a heat storage material size of about 5 to 6 μm. It was revealed that the particles synthesized under the condition of 10 wt% of sodium sulfate showed stable performance without a large change in the amount of heat storage after several measurements. In addition, it was suggested that the amount of stored sodium sulfate inside the particles could be controlled to some extent by changing the interaction between the polymer and sodium sulfate, as the amount of heat storage changed by changing the polymer concentration.

[Synthesis of capsule particles]
As described above, it was found that a capsule particle containing a heat storage material therein can be synthesized by dissolving a water-soluble polymer in an aqueous solution and using the dissolved polymer as a core. It was also suggested that the interaction between the polymer and sodium sulfate is related to the amount of sodium sulfate incorporated inside the particles. Although PEG was used as the polymer, it has been reported in the previous research that the hollow silica nanoparticles were successfully synthesized with polyacrylic acid (PAA) as the core. Therefore, in this example, capsule particles were similarly synthesized using various polymers, and the difference in their interaction was utilized to further improve the thermal characteristics. We also investigated the effect of emulsion on stability and particle formation, and evaluated its thermal characteristics to investigate the pervasiveness of application of this process.
The difference in the encapsulation behavior of sodium sulphate due to the difference in the electrostatic interaction was investigated by using the polymer having hydroxy group or carboxy group in the polymer chain.

〔material〕
FIG. 31 shows the structure of each polymer.

〔Production method〕
After adding HPC to octanol and stirring at 80° C. for 4 hours to completely dissolve it, the mixture was cooled to room temperature, Span 80 was added, and the mixture was stirred at 40° C. In another container, PAA, PVA, PVP, and PEI were added to water and dissolved, respectively, and then Teen 20 was added and stirred for 20 minutes. Then, aqueous ammonia was added to form an aqueous phase. This aqueous phase solution was added to the oil layer in a state of being stirred at 40° C. so that the ratio of water phase:oil phase was 1:9. Particles were prepared after stirring for 30 minutes. After completion of the reaction, centrifugation was performed and washing with ethanol was performed three times. After washing, it was dried overnight at 10° C. to obtain particles.
FIG. 32 shows a synthesis flowchart. Table 11 shows the reagent composition in that case. From the results of the previous example, the polymer concentrations were all set to 7.5 wt %.

[Evaluation]
a. SEM
An observation sample was prepared by fixing the dried particles to a brass sample stand to which a carbon tape was attached. Then, osmium was vapor-deposited by OSMIUM PLASMA COATER OPC60A (Filgen). For the observation, a scanning electron microscope (JSM-7000F, manufactured by JEOL) was used, and the acceleration voltage was 15.0 kV. Secondary Electron Image (SEI) mode was used for observation.
b. XRD measurement An X-ray diffraction pattern was measured using an X-ray diffractometer (RINT1000, manufactured by Rigaku) in order to confirm the crystal structure of sodium sulfate.
c. A differential scanning calorimeter (Thermo Plus DSC8230, manufactured by Rigak) was used to evaluate the thermal characteristics of the DSC measurement particles. The measurement was performed under the conditions of measurement range of endotherm and calorific value of −40° C. to 80° C., three cycles, and temperature rising/falling rate of 10° C./min. Further, the measurement was started from a state of being initially cooled to -40°C, heated to 80°C, and then cooled again to -40°C. The results show the results of the third measurement unless otherwise specified. In addition, the integrated value of the peak area was calculated using Thermo Plus2 standard software as the heat storage amount.
d. Viscosity measurement An aqueous solution of each polymer (7.5 wt%) and a mixed aqueous solution of sodium sulfate and polymer (sodium sulfate: 50 wt%, polymer: 7.5 wt%) were used for the rotary viscometer (HAAKE Rheo Stress manufactured by Thermo Fisher Scientific Co.). 6000) was used to measure the viscosity under the following conditions (shear speed 200 to 800 m/s, measurement time 60 s, cone c20/Ti).
e. TG measurement In order to quantify the amount of sodium sulfate contained in the polymer, PEG was added dropwise to the aqueous emulsion solution to dissolve PEG and the sodium sulfate incorporated therein was precipitated. The sample was then dried overnight at 10°C. After drying, the sample was heated to 1000° C. at 10° C./min and TG measurement was performed.

〔Results and discussion〕
33 to 36 show SEM and EDS images of particles synthesized under the conditions using each polymer. First, under the condition in which PAA in FIG. 33 was used as the polymer core, particles having a diameter of 4 μm, a slightly distorted spherical shape, and slight irregularities on the surface were observed. By EDS analysis, Na and S were strongly observed, and Si was spread over the entire field of view, which suggests that the crystals may be sodium sulfate. It can be seen that under the condition that PEI in FIG. 34 is used as the polymer core, particles of about 3 μm with a slightly rough surface are generated. Si was observed on the particles by EDS analysis, and Na and S spread over the entire visual field, suggesting that the particles may be silica particles. Under the conditions using PVA in FIG. 35, it was found that spherical particles having a particle size of about 6 μm and having a smooth surface were generated. Also, from the EDS analysis, stronger mapping of Si, Na, and S can be observed on the particles as compared with other particles. Therefore a possibility that sheet Rikasheru containing sodium sulfate therein is generated is suggested. However, from the results of SEM and EDS, it is difficult to determine whether sodium sulfate is present inside or is in a state of being attached on silica particles. Under the PVP conditions in FIG. 36, it was found that spherical particles having a smooth surface of about 4 μm were generated. EDS analysis clearly showed all mapping on the particles as well as PVA. Therefore a possibility that sheet Rikasheru containing sodium sulfate therein is generated is suggested. Moreover, the result of the XRD measurement of each sample is shown in FIG. The peak of sodium sulfate could be observed in any of the samples. However, some peaks in PAA and PEI conditions are decreasing. This indicates that the absolute amount of sodium sulfate contained in the sample is smaller than the other two. From the results of EDS and XRD alone, it is not possible to discuss whether sodium sulfate exists inside or outside the particles. However, from the above results, predictions can be made regarding the thermal characteristics. In other words, thermal characteristics are not observed under the conditions using PAA and PEI, which are considered to be completely separated from silica and sodium sulfate, and PVA and PVP that may contain sodium sulfate inside the particles It is expected that thermal properties can be observed under the conditions used. Therefore, the thermal characteristics were actually evaluated in the next DSC measurement.
FIG. 38 shows the DSC measurement result of each synthesized particle. From the results, it was possible to confirm the endothermic peak that appears due to the melting of the crystal at the time of temperature increase and the heat release peak due to the solidification of the crystal at the time of temperature decrease under the conditions using PVA and PVP. No peak can be confirmed under the conditions using PAA and PEI. This is in agreement with the trend expected from the EDS results. Table 12 shows the heat storage amount of each sample obtained from the DSC measurement results. Comparing the PVA and PVP type synthesized in this example with the condition of adding 7.5 wt% of the synthesized PEG in the previous example, it can be seen that the amount is reduced to about 1/5. This is considered to be due to the interaction between the polymer and sodium sulfate described below.

Subsequently, the viscosity of each polymer aqueous solution and the viscosity of each aqueous solution prepared by adjusting a 2M sodium sulfate aqueous solution to 50 wt% were measured. The results are shown in Fig. 39.
An aqueous solution of PVA alone has a very high viscosity of 300 mPa/s. On the other hand, the value with sodium sulfate added was much lower than that without sodium sulfate. This is probably because PVA was not sufficiently dissolved under the condition where sodium sulfate was added. Also in this example, under the conditions using PVA, when sodium sulfate was added, the solution became cloudy, and it was observed that undissolved sodium sulfate was dispersed in the solution. Therefore, it is speculated that the solubility of PVA in the solution containing sodium sulfate is significantly reduced. FIG. 40 shows the result of viscosity measurement excluding the conditions using PVA. What is shown by the broken line is the aqueous solution of the polymer alone, and what is shown by the solid line is the mixed aqueous solution of the polymer and sodium sulfate. As described above, the sodium sulfate aqueous solution was adjusted to be 50 wt %. Focusing on the tendency of each polymer, it is roughly divided into two types. PAA and PEI tended to have higher viscosity when sodium sulfate was added. On the other hand, in the case of using PVP, the decrease in viscosity was observed in the case of adding sodium sulfate.
Next, in order to investigate the effect of emulsion stability on the formation of capsule particles, the change in emulsion diameter with time for each polymer condition was examined using DLS. 40 to 43 show the DLS measurement results of each emulsion forming solution. First, paying attention to the PAA conditions in FIG. 41, it can be seen that the emulsion diameter varies greatly over time and is not stable. At 5 minutes, it is distributed over a wide range around 800 nm. It can be seen that after 30 minutes, the particle size was slightly reduced and a sharp peak was observed at 1 hour, resulting in an emulsion diameter of about 500 nm. Under the PEI condition of FIG. 41, it can be seen that there is no core as large as PAA at the beginning and it gradually enlarges with the passage of time and becomes smaller again after 1 h. It is considered that the emulsions are associated with each other and swelled with the passage of time, but the swelled emulsions collapsed after 1 h, and those having a small particle size remained. On the other hand, with other polymers, the emulsion size is relatively stable. In particular, under the condition using PVP in FIG. 43, a wide distribution of about 800 nm is shown at 5 minutes, but the particle size does not change even after a lapse of 15 minutes, 30 minutes, 1 hour, and is almost constant. Therefore, it is considered that the emulsion is stable with little change in diameter over time.
As mentioned above, the measurement of the viscosity and the emulsion diameter by DLS revealed that the behavior was different between the condition using PAA and PEI and the condition using PVA and PVP. Especially in PVP, it was suggested that the emulsion was more stable. One of these factors is considered to be the difference in electrostatic interaction between sodium sulfate and polymer. First, focusing on PEI, PEI is well known as a polymer having a high cation density. Therefore, electrostatic repulsion with sodium ion, which is also a cation, is considered to occur. In addition, it is considered that sodium sulfate is unlikely to precipitate inside the particles because it easily forms a complex with anions such as sulfate ions in the solution. It is also considered that the viscosity decreased because the molecular chain mobility decreased as compared to PEI alone due to the formation of a complex with sulfate ions. In addition, in both PAA and PVA, it was expected that sodium sulfate would be easily incorporated inside due to the electrostatic interaction of the carboxy and hydroxy groups contained in the molecular chain. However, as a result, capsule particles could be synthesized with PVA but not with PAA. This is considered to be a difference due to the strength of the electrostatic interaction between the two functional groups. Regarding PVP, factors different from other polymers are considered. As shown in FIG. 31, PVP is an amphipathic polymer having a hydrophilic group and a lipophilic group in one molecule. In an aqueous solution, it is known to associate the hydrophilic part on the outside and the lipophilic part on the inside. Therefore, it is considered that the mobility of the emulsion decreased due to the rapid association in water, and the stability of the emulsion diameter with the passage of time became higher than that of other polymers. In addition, regarding the decrease in viscosity when sodium sulfate is added, it is speculated that the adsorption of sodium sulfate to PVP in the associated state relaxes the associated state and increases the mobility of the molecular chain. It is considered that the viscosity was thereby decreased (see FIG. 44).

Through this example, it was revealed that the heat storage material-containing particles can be synthesized even when the polymer species used as the core is changed. It was clarified that some polymer particles could be used to synthesize capsule particles depending on the type of polymer used, and some were not, and it was suggested that this was due to the difference in molecular chain behavior due to hydrophobic interaction and interaction with the heat storage material. Therefore, it is considered essential to analyze in detail the interaction between the heat storage material and the polymer used during application, and it is considered necessary to select an appropriate polymer.

In the present invention, by encapsulating the heat storage material in the capsule particles, it can be expected to prevent leakage at the time of melting and to reduce phase separation. Therefore, Na ₂ SO ₄ ·10H ₂ O is used as PCM for microencapsulation. By applying the technology, heat storage material-encapsulating capsule particles were synthesized. Moreover, in the synthesis process, the influence of the synthesis conditions on the particle formation was discussed.
In Example 2, an aqueous sodium sulfate solution was added to a cyclohexane solvent to form a W/O emulsion, and the surface thereof was coated with silica to successfully synthesize capsule particles. It was revealed that the surfactant concentration mainly affects the particle size in the particle formation process. In addition, since the freezing point of PCM inside changes with the change of particle size, it is suggested that the freezing point can be controlled by controlling the particle size. Further, the reaction time required for particle formation was successfully reduced to 18 hours by using 3-3'diaminodipropylamine as a catalyst. At that time, it was found that the amino group (catalytic ability) of the catalyst and the viscosity are important factors.
In Example 2, a water-soluble polymer is dissolved in the aqueous phase, the viscosity of the aqueous solution is increased, and the dissolved polymer is used as a kind of core to synthesize heat storage material-encapsulating particles of about 5 to 6 μm. succeeded in. It was revealed that the particles synthesized under the condition of 10 wt% of sodium sulfate showed stable performance without a large change in the amount of heat storage after several measurements. In addition, it was suggested that the amount of stored sodium sulfate inside the particles could be controlled to some extent by changing the interaction between the polymer and sodium sulfate, as the amount of heat storage changed by changing the polymer concentration.
In Example 3, it was revealed that the heat storage material-containing particles can be synthesized even when the polymer to be dissolved in the aqueous phase is changed. It was suggested that there is a difference in the formation of capsule particles depending on the polymer used, and that it is due to the difference in the molecular chain behavior due to the hydrophobic interaction and the interaction with the heat storage material. Therefore, it is considered essential to analyze in detail the interaction between the heat storage material and the polymer used during application, and it is considered necessary to select an appropriate polymer.
As described above, it was clarified that by applying the microencapsulation technology to PCM, it is possible to synthesize heat storage material-encapsulating particles that do not deteriorate the heat storage performance even after repeated use. It was also clarified that the heat storage performance can be improved by using an appropriate polymer for the internal PCM. Similarly, it is considered that the composition can be applied to various PCMs other than Na ₂ SO ₄ ·10H ₂ O by selecting appropriate compounding ratios and manufacturing conditions.

According to the mixed viscous heat storage material and the method for producing the same according to the present invention, not only can it be used as a transparent heat storage paint or a transparent heat storage film, but it can also be used by kneading it into various coating materials or films.

Claims (6)

In the mixed viscous heat storage material of polymer and inorganic salt,
Polymer aqueous solution, polymer/sodium sulfate aqueous solution and water-soluble surfactant as an aqueous phase, octanol and a thickener as an oil phase,
Wherein by dropping tetraethylorthosilicate inorganic salts, mixing viscous regenerator, characterized in that sodium sulfate is formed inside the silica shell. The viscous regenerator, C. in 3-10Wt% aqueous solution of sodium sulfate, mixed viscous heat storage body according to claim 1, wherein the microencapsulated in 4 to 6 mu m. The mixed viscous heat storage material according to claim 1 or 2, wherein the aqueous phase is a combination of polyethylene glycol and sodium sulfate decahydrate. In the mixed viscous heat storage material of polymer and inorganic salt,
A polymer solution, a polymer / aqueous sodium sulfate and a water-soluble surfactant with the water phase, the octanol and thickener and the oil phase was added dropwise tetraethyl orthosilicate is the inorganic salts, stirred, by combining A method for producing a mixed viscous heat storage material, characterized in that sodium sulfate is formed inside a silica shell . The method for producing a mixed viscous heat storage body according to claim 4, wherein the viscous heat storage body is microencapsulated to a size of 4 to 6 μm in a 3 to 10 wt% sodium sulfate aqueous solution. The method for producing a mixed viscous heat storage material according to claim 4 or 5, wherein the aqueous phase is a combination of polyethylene glycol and sodium sulfate decahydrate.