Latent heat transfer material micro-encapsulated in hard shell, and production method for same

Abstract

Provided is a latent heat transfer material that is micro-encapsulated, said material exhibiting superior mechanical strength and heat resistance. A production method for the latent heat transfer material that is micro-encapsulated in a hard shell comprises: 1) a step in which a perforate hollow silica particle is manufactured; 2) a step in which the phase change material is sealed inside the perforate hollow silica particle by inserting the perforate hollow silica particle in a molten solution of the phase change material and repeatedly subjecting the same to vibrations such as ultrasound oscillations; 3) a step in which the perforate hollow silica particle having the phase change material sealed within is washed in a saturated aqueous solution of the phase change material; and 4) a step in which perhydropolysilazane is used to coat the outer shell of the perforate hollow silica particle with silica.

Claims

1. A hard shell microencapsulated latent heat transport material, comprising: non-porous hollow silica particles comprising porous hollow silica particles having outer shells covered by silica, the non-porous hollow silica particles having a phase change material included therein for causing absorption or discharge of latent heat in response to a temperature change.

2. A hard shell microencapsulated latent heat transport material according to claim 1, wherein further comprising: said phase change material having a phase change temperature at equal to or higher than 80 C. and equal to or lower than 600 C.

3. A hard shell microencapsulated latent heat transfer material according to claim 1, wherein further comprising: said phase change material in said non-porous hollow silica particle, not containing super cooling prevention agent and having smaller super cooling degree than the super cooling degree of said phase change material.

4. A hard shell microencapsulated latent heat transfer material according to claim 1, wherein further comprising: said porous hollow silica particle having a pore diameter of 10 nm200 m and having a particle diameter of 1 m4 mm.

5. A solid having ability to relax a temperature up and down movement, consisting of a material being a mixture or a mixed article of a hard shell microencapsulated latent heat transport material according to claim 1.

6. A thermally conductive fluid including a hard shell microencapsulated latent heat transport material according to claim 1, and a carrier fluid.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 A manufacturing flow of the hard shell microencapsulated latent heat transport material of embodiment 1

(2) FIG. 2 A schematic chart of the hard shell microencapsulated latent heat transport material synthesis of embodiment 1

(3) FIG. 3 A scanning electron microscope image of porous hollow silica particles

(4) FIG. 4 A scanning electron microscope of the non-porous hollow silica particles

(5) FIG. 5 A manufacturing flow of the hard shell microencapsulated latent heat transport material of embodiment 2

(6) FIG. 6 A DSC curve of the hard shell microencapsulated latent heat transport material of embodiment 2

BEST MODE FOR CARRYING OUT THE INVENTION

(7) Hereinafter, embodiments of the present invention will be described in detail below with reference to the drawings. The present invention is not limited to the following embodiment and examples of shown in the figure, and the present invention can be variously changed in design.

Embodiment 1

(8) One embodiment of the manufacturing method of the hard shell microencapsulated latent heat transfer material according to the present invention is explained.

(9) In embodiment 1, disodium hydrogen-phosphate is used as the phase change material. And preparation of the porous hollow silica particle is performed by the following sequence wherein water soluble sodium silicate and poly methyl methacrylate which is a water soluble compound for pore formation are mixed and the mixture is dispersed in an oil phase to be used for synthesis by interfacial reaction employing the W/O/W emulsion method.

(10) Disodium hydrogen-phosphate used as the phase change material is obtained by neutralization reaction of phosphoric acid and sodium salts (sodium hydroxides, sodium carbonates and so on) establishing bondages between 1 phosphoric acid and 2 sodium. There are two kinds of sodium phosphates, the first one is disodium hydrogen-phosphate (crystal) having water of crystallization and the second one is an anhydride of disodium hydrogen-phosphate (anhydride). Here, disodium hydrogen-phosphate (anhydride) is employed.

(11) The manufacturing method of the hard shell microencapsulated latent heat transport material according to embodiment 1 consists of the following 1)4) steps and each step out of the 4 steps is described below in detail. FIG. 1 shows a manufacturing flow of the hard shell microencapsulated latent heat transport material according to embodiment 1. And FIG. 2 shows a schematic chart of the hard shell microencapsulated latent heat transport material synthesis.

(12) 1) Preparation of Porous Hollow Silica Particles (S1)

(13) Water soluble sodium silicate and poly methyl methacrylate which is a water soluble compound for pore formation are mixed and the mixture is dispersed in an oil phase to be used for synthesis by interfacial reaction employing the W/O/W emulsion method.

(14) 2) Enclosure of a Melting Liquid of the Phase Change Material (S2)

(15) By adding porous hollow silica particles to a melting liquid of disodium hydrogen-phosphate which is a phase transition material and subsequently repeating shaking, disodium hydrogen-phosphate is enclosed in the porous hollow silica particles.

(16) 3) Washing of Porous Hollow Silica Particles (S3)

(17) Porous hollow silica particles enclosing disodium hydrogen-phosphate are centrifuged and washed by quasi saturated aqueous solution of disodium hydrogen-phosphate.

(18) 4) Coating of Porous Hollow Silica Particles by Silica (S4)

(19) Coat the outer shell of the washed porous hollow silica particles after washing, with silica using perhydropolysilazane (PHPS)

(20) <Preparation of Porous Hollow Silica Particles>

(21) Water phase 1, oil phase 1 and water phase 2 at the W/O/W emulsion method are explained.

(22) (a) Water Phase 1

(23) 30 gram of 30% concentration sodium silicate aqueous solution and 10 gram of methyl poly methacrylate (molecular weight 9500) aqueous solution and the volume thereof is adjusted to become 36 ml by adding water.

(24) (b) Oil Phase 1

(25) 72 ml of n-hexane, 1 g of surfactant Tween 80 (Polyoxyethylene Sorbitan Monooleate) and 0.5 g of Span 80 (Sorbitan Monoleate) are mixed. (Teen and Span are trademarks)

(26) (C) Water Phase 2

(27) 250 ml (2 mol/l) of ammonium hydrogen carbonate is prepared. (About 39.8 g of ammonium hydrogen carbonate is poured and adjusted to become 250 ml by adding water)

(28) At first, water phase 1 and oil phase 1 are mixed for 1 minute at 8200 rpm using a mixing type homogenizer (refer to FIG. 2 (a)). And the mixture and the water phase 2 are mixed and stirred using a magnetic stirrer for 2 hours at 35 C. (refer to FIG. 2 (b))

(29) Next, the mixture is washed 3 times by water and 1 time by ethanol, and is dried at 100 C. for 12 hours and after that, the mixture is calcined by a condition that 700 C. is reached within 60 minutes.

(30) By the process mentioned above, the porous hollow silica particles are prepared. (Refer to FIG. 2 (c))

(31) By the preparation method described above, the volume ratio for three phases are set as follows; water phase 1:oil phase 1:water phase 2=1:1:7. The volume ratio is not limited to the above and can be adjusted, accordingly. For example, a solution of a ratio 1:8:7 wherein oil ratio is different from the above can prepare the porous hollow silica particles without any problems.

(32) FIG. 3 shows one example of a scanning electron microscope image of prepared porous hollow silica particles. The porous hollow silica particles shown in FIG. 3 have diameters of about 50 m, having innumerable pores. Also, the pore diameter is about 0.5 m.

(33) <2. Enclosure of a Melting Liquid of a Phase Change Material>

(34) An appropriate volume of disodium hydrogen-phosphate which is a phase change material is poured into a beaker and the disodium hydrogen-phosphate is melted at 5065 C.

(35) And, the porous hollow silica particles prepared were poured into melting liquid of disodium hydrogen-phosphate, which is stirred by a magnetic stirrer. (Refer to FIG. 2 (d)) Under a condition wherein the temperature of the melting liquid of disodium hydrogen-phosphate is kept as accurately as possible, the melting liquid of disodium hydrogen-phosphate is enclosed in the porous hollow silica particles by repeated mechanical shocks using ultrasonic radiation or a vortex mixer. (Refer to FIG. 2 (e))

(36) <3. Washing of Porous Hollow Silica Particles>

(37) A mixture of the disodium hydrogen-phosphate melting liquid and the porous hollow silica particles is centrifuged. Then, the porous hollow silica particles are washed by using quasi saturated aqueous solution of disodium hydrogen-phosphate after eliminating the supernatant. The purpose of this procedure is to eliminate the excess disodium hydrogen-phosphate outside of the capsule.

(38) <4. Coating of Porous Hollow Silica Particles by Silica>

(39) After washing the porous hollow silica particles with quasi saturated aqueous solution of disodium hydrogen-phosphate, the supernatant is eliminated. After adding perhydropolysilazane (PHPS) to the porous hollow silica particles after eliminating the supernatant, the porous hollow silica particles are calcined for 34 hours at 200 C. (Refer to FIG. 2 (f)) By this procedure, the outer shell of the porous hollow silica particles can be covered by silica and the hard shell microencapsulated latent heat transport material consisting of non-porous hollow silica particles including disodium hydrogen-phosphate which is a phase transition material can be obtained.

(40) FIG. 4 shows one image example of scanning electron microscope of the non-porous hollow silica particles thus obtained. In the image shown in FIG. 4, pores cannot be observed at the outer shell surface of the silica particles and it is known that the outer shell is completely covered by silica.

(41) The silica particles shown in FIG. 4 includes disodium hydrogen-phosphate (the phase change material) and functions as a hard shell microencapsulated latent heat transfer material. Perfect coverage of the outer shell by silica improves the mechanical strength and heat resistivity of the capsule. The silica particles described here are not crushed by a transport pump or so on when latent heat transport is performed and are chemically stable and superiorly corrosion resistant.

Embodiment 2

(42) In embodiment 2, by another method different from the method according to embodiment 1, the preparation method of the hard shell microencapsulated latent heat transport material including trimethylolethane (TME) is explained.

(43) The TME hydrate has its phase transition temperature at about 15 C. and the phase transition temperature can be adjusted by controlling its concentration. The TME hydrate has a latent heat of 218 (kJ/kg) and its use as a cooling medium of air conditioning systems is expected.

(44) The encapsulation sequence of trimethylolethane (TME) into the hard shell microcapsule is explained below.

(45) The manufacturing method of the hard shell microencapsulated latent heat transport material according to embodiment 2 consists of the following a)d) steps with the flow shown in FIG. 5.

(46) a) Preparation of Porous Hollow Silica Particles (S21)

(47) Water soluble sodium silicate and poly methyl methacrylate which is a water soluble compound for pore formation are mixed and the mixture is dispersed in an oil phase to be used for synthesis by interfacial reaction employing the W/O/W emulsion method.

(48) b) Enclosure of Melting Liquid of the Phase Change Material (S22)

(49) Porous hollow silica particles are poured into the melting liquid of trimethylolethane (TME) which is a phase change material and trimethylolethane (TME) is enclosed in the porous hollow silica particles by decompression.

(50) c) Washing of Porous Hollow Silica Particles (S23)

(51) Porous hollow silica particles having trimethylolethane (TME) enclosed are centrifuged and washed with quasi saturated aqueous solution of trimethylolethane (TME).

(52) d) Coating of Porous Hollow Silica Particles by Silica (S24)

(53) Sodium silicate solution is dropped on the outer shell of the washed porous hollow silica particles and, after that, ammonium carbonate solution is dropped and the porous hollow silica particles are dried to have the outer shell coated with silica.

(54) Below, b)d) mentioned above are explained in detail. Note that a) above is similar to the one explained in embodiment 1 and the explanation is omitted here.

(55) First of all, microcapsules are immersed in TME 25 weight percent aqueous solution inside a test tube. Next, the test tube is decompressed with a 5 (KPa) vacuum pump for 1 hour in order to eliminate air from the inside of the microcapsules. After that, the microcapsules filled with TME are centrifuged to be separated from the residual TME solution. After the separation, the microcapsules are cooled and dried for 1 day.

(56) Next, for covering the pores of microcapsule, 2 mL of sodium silicate solution (10 g, 30% of SiO.sub.2 in 12 mL of water) is dropped on 0.3 g of microcapsules dried under stirring. Furthermore, 2 mL of ammonium carbonate solution (2 mol/L) is dropped on the microcapsules. And, after stirring for 2 hours at 35 C., the microcapsules containing TME hydrate are dried for 1 day at a room temperature.

(57) By the process described above, the pores of microcapsules containing TME hydrate are completely closed. Note that the median diameter of microcapsules containing TME hydrate was 19.0 m.

Embodiment 3

(58) FIG. 6 shows a DSC curve (differential scanning calorimeter) of the hard shell microencapsulated latent heat transport material (TME inclusion hard shell microcapsule) including trimethylolethane (TME) and the endothermic peak of a trimethylolethane (TME) solution of 25 weight percent. The latent heat of the TME solution measured here was about 90.4 (J/kg) and the phase change temperature of the same was 16.8 C. The theoretical latent heat value of the TME 25 weight percent solution is 87.2 (kJ/kg) and this value was in good agreement with the measured value.

(59) Also, for the two heating cycles, the measured latent heats of the hard shell microcapsules including TME were 38.8 (kJ/kg) and 48.6 (kJ/kg), respectively and the corresponding phase change temperatures were 14.8 C. and 18.5 C., respectively. Also, supercooling (a phenomenon wherein a phase does not change at the phase change temperature) is observed and the measured phase change temperatures were 15.3 C. and 15.5 C. Note that, in the graph of FIG. 6, the phase change temperature during a heating cycle is shown to be 18.5 C. and the phase change temperature during a cooling cycle is shown to be 15.3 C.

(60) From the temperature rise curve and the temperature going down curve, it is understood that the phase change temperature of the TME inclusion hard shell microcapsules is similar to the phase change temperature of the 25 weight % TME solution. However note that, in the temperature going down curve, the coagulation temperature of the hard shell microencapsulated TME is 15.3 C. and the coagulation temperature of the TME solution is 3.3 C. From this result, it is understood that the hard shell microcapsule including TME has smaller degree of super cooling than the TME solution.

(61) Also, the mass ratio of the TME hydrate in the microcapsule to the whole mass of the hard shell microcapsule including TME was about 54.4 wt. % calculated from the particle diameter. 54.4 wt. % of 87.2 (kJ/kg) (the latent heat of TME solution at 25 wt. %) is 47.4 (kJ/kg) and this represents the measured latent heat as mentioned above, namely 48.6 (kJ/kg). The above mentioned 48.6 (kJ/kg) well corresponds to the value 47.4 (kJ/kg) calculated from the mass ratio.

(62) Therefore, the hard shell microcapsule including TME prepared has been confirmed to include TME hydrate. Also, it can be said that the endothermic and the exothermic peaks show enough inclusion of TME hydrate inside the microcapsule, with TME hydrate inside the microcapsule being not vaporized.

The Other Embodiment

(63) In the embodiment 1 mentioned above, disodium hydrogen-phosphate was employed as a phase change material. However, by the non-porous hollow silica particles, various phase change materials that change their phases at any temperature below 600 C. can be utilized as the phase change material, being superior in mechanical strength and heat resistivity. For example, as the phase change materials having high phase transition temperature (80500 C.), the materials listed in the table 1 below can be applied. The other phase change materials having the transition temperature below 600 C. can also be utilized.

(64) TABLE-US-00001 TABLE 1 Phase transition Material temperature ( C.) Molten salt LiOHNaOH (30:70) 458 NaOHKOH (50:50) 444 Organic matter Pentaerythritol 188 Poly-ethylene 120-140 Sorbitol 95 Xylitol 92 Propionamid 81.3 Inorganic hydrate MgCl*6H.sub.2O 116-118 Al.sub.2(SO.sub.4).sub.3*10H.sub.2O 112 NH.sub.4Al(SO.sub.4).sub.2*12H.sub.2O 93.5 KAl(SO.sub.4).sub.2*12H.sub.2O 92.5 Mg(NO.sub.3).sub.2*6H.sub.2O 89 Sr(OH.sub.2)*8H.sub.2O 88

INDUSTRIAL APPLICATION POSSIBILITY

(65) This invention is useful as a heat medium of a heat transport device that recovers high temperature heat waste and transport the same to the place where heat is necessary.