KR100337025B1 - Process for Microencapsulat ed Phase Change Material Slurry - Google Patents

Abstract

The present invention relates to a method for preparing a microcapsule latent heat particulate slurry. More specifically, by using in situ polymerization method, phase change material such as paraffinic oil (hereinafter referred to as PCM) can be used as a melamine-formaldehyde resin to be used simultaneously as a heat storage and heat supply medium. A method for producing an encapsulated microcapsule latent heat particulate slurry.

The phase change material is dispersed and emulsified in aqueous solution using an anionic surfactant, PSSA (Poly Styrene Sulfonic Acid), and then the melamine-formaldehyde (MF) resin corresponding to the capsule wall is reacted by in-situ polymerization. It is composed of a process for producing a latent heat particulate slurry.

In this method, microcapsule-type latent heat fine particles having durable walls are manufactured by using a polymer, which is a wall material, to minimize PCM leakage and to increase efficiency as a heat storage medium. Capsules can be prepared.

Description

Process for producing microcapsule latent heat particulate slurry {Process for Microencapsulated Phase Change Material Slurry}

The present invention relates to a method for preparing a microcapsule latent heat particulate slurry. More specifically, by using in situ polymerization method, phase change material such as paraffinic oil (hereinafter referred to as PCM) can be used as a melamine-formaldehyde resin to be used simultaneously as a heat storage and heat supply medium. A method for producing an encapsulated microcapsule latent heat particulate slurry.

All materials change phase according to temperature, and when phase change, materials absorb or release heat without temperature change. At this time, the heat absorbed or released is called latent heat. The use of latent materials, which cause phase changes within the temperature range, can increase the heat storage density.

The microencapsulation method that prevents the outflow of phase change material by using phase change material with high latent heat as internal material and using polymer with compact structure and durability can add new functions different from the method using phase change material. Can be.

The microcapsules are mainly used in the pharmaceutical and food fields. The encapsulation method is known as physical method, mechanical method, and physicochemical method, but the mechanical process method has been applied to the production of capsules of a certain size. There have been many approaches to chemical methods.

Conventional encapsulation technology of the phase change material has been used to prepare the epidermal material first by a mechanical method and to encapsulate the internal material, and then the capsule has been manufactured by a coating method by nozzle injection. In addition, it is a method of storing and using in a flexible container so as to exclude the aggregation and condensation during the phase change of the phase change material and to maintain the particulate properties continuously (KR Sanjay and S. Sengupta, Int. Comm. Heat M ass Transfer , 18, p495-507, 1990) have attempted air conditioning applications over a wide temperature range. The diameters of capsules using conventionally manufactured methods are mainly 3 to 9 cm in diameter, and recently, a technique for producing 2 to 3 mm spherical particles using a spray coater (HK Lee and JH Park, United States Patent 5,709,945, Jan. 20, 1998).

To date, phase change materials have been used for static heat storage, while latent heat particulates are a dynamic concept in the form of a slurry mixed with a transfer medium such as water (H. Takeuchi, AT Pyatenko, IEEE 96082). , 1998) and can also be used for heat transport. When used for heat storage, it is possible to maintain uniform melt without supercooling and phase separation even after repeated heat absorption and release due to the inherent characteristics of capsules, and to maintain the characteristics of continuous phase change materials by preventing aggregation and condensation between phase change materials. . When used in the slurry state for heat storage and transportation, it has the effect of improving the heat transfer efficiency by increasing the micro-convection effect in the fluid.The surface area is increased through atomization of particles, so the heat absorption and release rate is faster, so the heat exchanger heat transfer area is increased. It is small, there is an advantage that the heat transfer density is increased, the heat transfer power is reduced.

In the present invention, in situ polymerization was used as a method for preparing microcapsules. The manufacturing process includes an emulsification process of dispersing a paraffinic oil, which is a phase change material in an aqueous solution, and a condensation reaction of melamine and formaldehyde outside the emulsified oil. A polymer reaction process to form the shell is included. An important procedure in the manufacturing process lies in the selection of a suitable surfactant that allows the melamine-formaldehyde prepolymer to act to be uniformly positioned around the inner phase droplets without destroying the emulsified emulsion. In the present invention, a hydrophilic anionic surfactant was used to prepare a capsule in which agglomeration was not generated while maintaining a uniform size. These protective colloids form a solid and charge boundary layer around each droplet by aligning at the inner phase / outer phase interface in the emulsification step to stabilize the emulsion and prevent the agglomeration caused by the contact between the droplets. It serves to maintain. In addition, the polymerization step of forming the wall crosslinks the partially positively charged melamine-formaldehyde wall material to help the emulsion to stably form the microcapsules. The capsules produced by the in situ polymerization method have the same process of forming the walls of the capsule by polymerization at the interface between the inner phase (oil) and the continuous phase (water), but fundamentally different from the capsules made by the interfacial polymerization. There is. Interfacial polymerization is a method in which polymerization occurs by contacting monomers dissolved in different phases at an interface, but in situ polymerization method used in the present invention is almost carried out by rapid self-condensation reaction at the interface between monomers and dimers of water-soluble amino resins. Microcapsules with a complete polymer shell structure are formed. In the case of interfacial polymerization, which has been used as a microencapsulation method of liquid materials until now, polymerization is possible at a short time at room temperature, but there is a disadvantage in that the wall material is weak and easily broken and the durability is not good for a long time, and the volume of the reaction system is large. The in-situ polymerization method used in this study enables encapsulation of high concentration and high yield, and takes longer reaction time than interfacial polymerization, but obtains a robust and durable capsule. The reaction temperature varies depending on the curing temperature of the material, and usually, since the reaction temperature is higher than the normal temperature, an additional cost for temperature control is required. The two reactants each react in a continuous phase to form a prepolymer, with the polymerization continuing as the size of the prepolymer grows and ultimately the melamine-formaldehyde prepolymer separates into many phases. The crosslinking and polymerization of the prepolymer in aqueous solution depends on the nature of the inner material surrounded by the protective colloid and continues to polymerize until the capsule wall material is completed. In situ polymerization, compared to interfacial polymerization, was used to have high yields and robust and durable wall materials. In situ polymerization was used to suit these properties, which require elasticity in the expansion and contraction of volume due to the phase change of internal materials. The capsules with the melamine-formaldehyde resin film used for this reason are superior to other urea resins in that they are resistant to temperature, humidity, and solvents, but the capsules have an increased viscosity when reacting in aqueous solution or aggregate between particles. There is a difficulty of manufacturing. In order to maintain the protective colloid function and low viscosity in the emulsification step, a microcapsule slurry was prepared using PSSA. The in-situ polymerization method of the present invention can improve the encapsulation yield of a high concentration capsule slurry and injected phase change material.

1 is a process chart of the present invention for preparing a microcapsular latent heat particulate by in situ polymerization method.

2 is a photograph showing a microcapsule shape of the present invention.

3 is a graph showing the particle size distribution of the microcapsules of the present invention.

The present invention will be described in detail with reference to the accompanying drawings as a means for achieving the object as described above and solving the conventional problems as follows.

1 is a microcapsules manufacturing process chart by the in situ polymerization method of the present invention. A jacket-type reactor was used to control the reaction temperature, and the volume ratio of paraffinic oil intedecane (tetradec ane) used as a phase change material and distilled water introduced into the reactor was maintained at 3: 1. The melamine-formalin resin, which will form the microcapsule wall, is mixed at a molar ratio of melamine and formalin at 1: 1.73-1: 2.5 and polymerized at 60 ° C. In the present invention, the surfactant is an anionic surfactant, and a polystyrene sulfonic acid (hereinafter referred to as PSSA) having a molecular weight of 500,000 and a pH of 10wt% aqueous solution at room temperature is 8.0. PSSA, an anionic surfactant, is used to prepare capsules that do not generate aggregation between particles while maintaining a uniform size.

10 g of PSSA was mixed with 90 g of water, stirred at 80 ° C. for 30 minutes, dissolved, cooled, mixed with 100 g of water in 100 g of 10 wt% PSSA aqueous solution, and 70 g of Tetracanane oil corresponding to the internal substance was used at 3,700 rpm. Emulsify sufficiently for minutes to form an emulsion solution.

Thereafter, melamine monomer and formalin (formalin, a typical 37% Formaldehyde aqueous solution) were mixed at a molar ratio of 1: 1.73-1: 2.5, and 3-5 g of glutaraldehyde was added thereto, followed by stirring for 1 minute. After polymerization by adjusting the pH to 4-5 with HCl aqueous solution. At this time, the reaction temperature is maintained at 60 ℃, the reaction time lasts about 4 hours.

Melamine-formalin resins affecting the properties of the capsule wall generally improve the durability of the wall material by controlling the amount of melamine and formalin. In addition, formalin and glutaraldehyde are used to cure the microcapsules to improve the durability of the wall material.

The following examples are representative of the processes for preparing microcapsules of the present invention and these examples do not limit the technical scope of the present invention.

As a reactor of the present invention, a 1 L dual reactor is prepared to maintain stirring and constant temperature, and an stirrer for mechanical stirring and an impeller composed of four wings are used. Tetradecane, an internal substance, was added to the PSSA aqueous solution in the reactor and emulsified at room temperature. Then, melamine and formalin substances corresponding to wall materials were added and the reaction was performed at 60 ° C.

<Example 1>

Step 1: Mix 100 g of 10 g polystyrene sulfonate (PSSA) with 90 g of water, stir at 80 ° C. for 30 minutes, dissolve, and prepare 100 g of cooled 10 wt% PSSA solution.

Step 2: Add 100 g of water to the 10 wt% PSSA aqueous solution of step 1, stir for 1 minute, add 70 g of tetradecane, and emulsify to form an emulsion mixture. The oil is dispersed for 3 minutes at a stirring speed of 1700 rpm at room temperature.

Step 3: 15 g of melamine corresponding to the wall material, 18 g of formalin, and 3 g of glutaraldehyde were added to the mixed solution of the second step (100 g of water, 70 g of tetradecane, emulsified and oil-dispersed in 10 wt% PSSA aqueous solution). Stir for 1 minute.

Step 4: 0.5N of the mixed solution of step 3 (100g of water, 70g of tetradecane was added to an aqueous 10 wt% PSSA solution, emulsified, and 15g of melamine, 18g of formalin, and 3g of glutaraldehyde were added to the oil-dispersed solution). Into the aqueous solution of HCl to adjust the pH value corresponding to the crosslinking conditions of the melamine-formalin resin to maintain a pH of about 4.0.

Step 5: The solution of step 4 is polymerized at 60 ° C. for 4 hours while maintaining a stirring speed of 550 rpm.

Step 6: In order to spray dry the polymerized slurry obtained in step 5, the temperature of the hot air fan was set at 200 ° C., and preheated until the temperature of the drying reactor was 160 to 170 ° C., and then the microcapsule slurry was 10 ml by a pump. The microcapsule type latent heat particulate slurry was prepared by blowing air at 7 to 9 bar while simultaneously conveying the air per minute or less.

<Example 2>

Step 1: The same procedure as in Example 1.

Step 2: The same procedure as in Example 1.

Step 3: The same procedure as in Example 1.

Step 4: The procedure is the same as that in Example 1 except that the pH is maintained at 4.0 to 5.0.

Step 5: The same procedure as in Example 1.

Step 6: The same procedure as in Example 1.

<Example 3>

Step 1: The same procedure as in Example 1.

Step 2: The same procedure as in Example 1.

Step 3: Add 15 g of melamine, 20 g of formalin, and 65 g of water, and mix for 30 minutes at 60 ° C to make a prepolymer. This is added to the mixed solution of the two steps and stirred for 1 minute.

Step 4: Adjust the pH value corresponding to the crosslinking condition of the MF resin by adding 0.5N HCl aqueous solution to the mixed solution of step 3, which maintains the pH of about 4.0 to 5.0.

Step 5: The same procedure as in Example 1.

Step 6: The same procedure as in Example 1.

<Example 4>

Step 1: The same procedure as in Example 1.

Step 2: 100g of water is added to the solution of step 1, followed by stirring for 1 minute, followed by emulsification by adding 70g of tetradecane to form an emulsion mixed solution. Oil dispersion is performed at room temperature for 3 minutes at a stirring speed of 1700 rpm.

Step 3: Melamine 20g, formalin 40g, glutaraldehyde, 5g, 55g of water to the wall material was added to the stirred mixture at 60 ℃ for 30 minutes to prepare a prepolymer and stirred for 1 minute.

Step 4: The pH value corresponding to the crosslinking condition of the MF resin is adjusted by dropwise addition of 0.5N HCl aqueous solution to the mixed solution of step 3 and maintained at pH 4.0 to 5.0.

Step 5: The same procedure as in Example 1.

Step 6: The same procedure as in Example 1.

<Example 5>

Step 1: The same procedure as in Example 1.

Step 2: 100g of water is added to the solution of step 1, followed by stirring for 1 minute, followed by emulsification by adding 70g of tetradecane to form an emulsion mixed solution. Oil dispersion is performed at room temperature for 3 minutes at a stirring speed of 1700 rpm.

Step 3: 20 g of melamine, 35 g of formalin, and 5 g of glutaraldehyde are added to the mixed solution of step 2 and stirred for 1 minute.

Step 4: The pH mixture corresponding to the cross-linking conditions of the MF resin is maintained by adding 0.5N HCl aqueous solution to the mixed solution of step 3 and maintaining the pH at about 4.0 to 5.0.

Step 5: The same procedure as in Example 1.

Step 6: The same procedure as in Example 1.

The microcapsular latent heat particulates obtained by the in situ polymerization method of the present invention react with water or nucleophilic substances at the dispersed oil interface to form a prewall around the inner phase, which is stable and high in strength. . The final microcapsules have an average size of 20 μm as shown in FIG. 2 and can be mass-produced at one time with easy control and encapsulated in a short time. In addition, it can be manufactured in a much finer size than the capsule produced by the conventional mechanical method, and the cross-linking degree is increased compared to the interfacial polymerization method produced by the chemical method, resulting in improved durability and a microcapsule type with a very smooth surface structure. The latent heat fine particles have the advantage that the surface area is increased when flowing from the heat storage or transport to the slurry medium, so that the absorption and release rate of heat is faster and the power required for constant heat transport is reduced.

Claims (5)

In the method for producing a microcapsule latent thermal particulate slurry, a step of preparing a PSSA aqueous solution that is cooled by mixing polystyrene sulfonic acid (PSSA) and water, stirred at 80 ° C. for 30 minutes, dissolved, and Water was added to the PSSA aqueous solution and stirred to add Tetradecane as a phase change material, followed by emulsification to form an emulsion mixed solution, and then dispersing the phase change material at room temperature. Melamine, formalin, Adding 3 to 5 g of glutaraldehyde and stirring the mixture, adjusting HCl to the pH of the melamine-formalin resin to suit the crosslinking conditions, and stirring the solution at 60 ° C. at a stirring rate of 550 rpm. Obtaining a slurry by polymerization for 4 hours, and spray drying the polymerized slurry. Method for preparing microcapsule latent heat particulate slurry The microcapsule-type latent heat particulate slurry according to claim 1, wherein the PSSA aqueous solution is a 10 wt% PSSA aqueous solution which is cooled by mixing 90 g of water in 10 g of polystyrene sulfonate and stirring at 80 ° C. for 30 minutes to dissolve. Way. The method of claim 1, wherein the step of dispersing tetradecane, a phase change material, adds 100 g of water to a 10 wt% PSSA aqueous solution and stirs for 1 minute to add 70 g of tetradecane and emulsifies the mixed solution in an emulsion state at room temperature. Method for producing a microcapsule type latent heat particulate slurry, characterized in that the step of dispersing tetradecane at 1700rpm for 3 minutes. According to claim 1, wherein the step of adjusting the pH suitable for the crosslinking conditions of the melamine-formalin resin is added to the mixed solution of the melamine, formalin, glutaraldehyde 3-5g and stirred for 1 minute 0.5N of the mixed solution Method of producing a microcapsule-type latent heat particulate slurry, characterized in that the step of adding an aqueous solution of HCl to adjust the pH to 4.0 to 5.0. 5. The method of claim 1 or 4, wherein the molar ratio of melamine and formalin in the addition of melamine and formalin is 1: 1.73 to 1: 2.5.