Method for preparing spherical magnesium oxide composite and spherical magnesium oxide composite prepared thereby

Abstract

The present invention provides a method for preparing a spherical magnesium oxide composite, and a spherical magnesium oxide composite prepared thereby, the method comprising: a slurry preparation step of forming a slurry by mixing a magnesium oxide precursor comprising at least one of Mg(OH)2 powder and MgO powder, an inorganic additive, a dispersant, and water; a pH adjustment step of adjusting the pH of the slurry by using a pH adjusting agent; a spray drying step of preparing granular powder from the slurry by using a spray drying method; and a sintering step of subjecting the granular powder to sintering treatment to crystallize the granular powder.

Description

Method for manufacturing a spherical magnesium oxide composite and a spherical magnesium oxide composite manufactured thereby

[0001] The present invention relates to a method for manufacturing a spherical magnesium oxide composite and a spherical magnesium oxide composite manufactured thereby.

[0002] Electronic devices consist of electronic components such as laminates, printed circuit boards, and multilayer circuit boards. Recent electronic devices are equipped with high-capacity power components and manufactured with high-density internal configurations for miniaturization, requiring a higher level of heat dissipation and weight reduction compared to conventional devices. Silica and alumina have been primarily used as fillers in resin compositions for conventional semiconductor encapsulation. However, due to its low thermal conductivity, silica lacks sufficient heat dissipation capacity to handle the increased heat generation resulting from high integration, high power consumption, and high speeds, which poses a problem for the stable operation of semiconductors. On the other hand, while alumina, which has higher thermal conductivity than silica, offers improved heat dissipation, its high density and excessive hardness lead to severe wear on mixing machines, molding machines, and molds.

[0003] Accordingly, magnesium oxide, which possesses higher thermal conductivity and a relatively lower density compared to alumina, is being considered as a material for semiconductor encapsulation resin fillers. However, magnesium oxide powder has a problem in that it cannot maintain stable physical properties due to its higher hygroscopicity compared to alumina powder. Specifically, when magnesium oxide powder is used as a semiconductor encapsulation resin filler, the magnesium oxide reacts with moisture in the air to form magnesium hydroxide on its surface, causing the volume of the filler to expand. This leads to problems such as crack formation and a decrease in thermal conductivity.

[0004] Therefore, in order to effectively use it as a heat dissipation filler, research is needed to manufacture magnesium oxide that has a spherical shape without surface cracks and possesses improved moisture resistance.

[0005] [Prior Art Literature]

[0006] [Patent Literature]

[0007] Republic of Korea Registered Patent Publication No. 10-1878963

[0008] The present invention aims to provide a method for effectively manufacturing a spherical magnesium oxide composite with improved moisture resistance and a spherical magnesium oxide composite manufactured using the same.

[0009] However, the technical problems that the present invention aims to solve are not limited to those mentioned above, and other unmentioned problems will be clearly understood by those skilled in the art from the description below.

[0010] One embodiment of the present invention provides a method for manufacturing a spherical magnesium oxide composite, comprising: a slurry preparation step of mixing a magnesium oxide precursor comprising at least one of Mg(OH)2 powder and MgO powder, an inorganic additive, a dispersant, and water to form a slurry; a pH adjustment step of adjusting the pH of the slurry using a pH adjuster; a spray drying step of manufacturing the slurry into granular powder using a spray drying method; and a sintering step of crystallizing the granular powder by sintering treatment.

[0011] Another embodiment of the present invention provides a spherical magnesium oxide composite produced by the above manufacturing method.

[0012] The method for manufacturing a spherical magnesium oxide composite according to the present invention can produce a magnesium oxide composite having high sphericity and hygroscopicity in a simple manner. In addition, the method for manufacturing a spherical magnesium oxide composite according to the present invention has the advantage of being able to produce spherical magnesium oxide composites of a desired size in large quantities by controlling the rotation speed and the solid content of the slurry during the spray drying step.

[0013] The effects of the present invention are not limited to those mentioned above, and other unmentioned effects will be clearly understood by a person skilled in the art from the description below.

[0014] Figure 1 is a graph showing the sphericity trend of sintered particles according to the pH of the slurry and the solid content of the slurry, based on the composition as in the example.

[0015] Figure 2 shows an SEM image of sintered particles prepared according to Comparative Example 1.

[0016] Figure 3 shows an SEM image of sintered particles prepared according to Comparative Example 2.

[0017] Figure 4 shows an SEM image of sintered particles prepared according to Comparative Example 3.

[0018] Figure 5 shows an SEM image of sintered particles prepared according to Example 2.

[0019] Figure 6 shows an SEM image of sintered particles prepared according to Example 4.

[0020] Figure 7 shows an SEM image of sintered particles prepared according to Example 6.

[0021] Figure 8 shows an SEM image of sintered particles prepared according to Example 9.

[0022] Figure 9 shows an SEM image of sintered particles prepared according to Example 10.

[0023] Figure 10 shows an SEM image of sintered particles prepared according to Comparative Example 4.

[0024] Figure 11 shows an SEM image of sintered particles prepared according to Comparative Example 5.

[0025] Figure 12 shows the XRD analysis results before and after a 72-hour test at 85°C and 85%RH of sintered particles prepared according to Example 4.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by a skilled expert in the art to which this invention pertains. In general, the nomenclature used herein is well known and commonly used in the art.

[0027] The present invention is susceptible to various modifications and may have various embodiments, and specific embodiments are to be described in detail in the detailed description. However, this is not intended to limit the present invention to specific embodiments, and it should be understood that it includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the present invention. In describing the present invention, detailed descriptions of related prior art are omitted if it is determined that such detailed descriptions may obscure the essence of the present invention.

[0028] The terms used in this specification are used merely to describe specific embodiments and are not intended to limit the invention. The singular expression includes the plural expression unless the context clearly indicates otherwise.

[0029] In this specification, when a part is described as "comprising" a certain component, it means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0030] In this specification, when a member is described as being located "on" another member, this includes not only cases where a member is in contact with another member, but also cases where another member exists between the two members.

[0031] The present invention will be described in detail below.

[0032] One embodiment of the present invention provides a method for manufacturing a spherical magnesium oxide composite, comprising: a slurry preparation step of mixing a magnesium oxide precursor comprising at least one of Mg(OH)2 powder and MgO powder, an inorganic additive, a dispersant, and water to form a slurry; a pH adjustment step of adjusting the pH of the slurry using a pH adjuster; a spray drying step of manufacturing the slurry into granular powder using a spray drying method; and a sintering step of crystallizing the granular powder by sintering treatment.

[0033] Slurry manufacturing step

[0034] The above slurry preparation step may involve preparing a mixture by mixing a magnesium oxide precursor containing at least one of Mg(OH)2 powder and MgO powder, an inorganic additive, a dispersant, and water, and then slurrying the mixture.

[0035] In the above slurry preparation step, Mg(OH)2 powder and / or MgO powder may be used as a precursor for magnesium oxide. When MgO is used as a precursor for magnesium oxide, since it reacts with water (H2O) as a solvent and is entirely converted into Mg(OH)2, using MgO powder as a precursor in an aqueous system can be substantially the same as using Mg(OH)2 powder.

[0036] Water is used as the solvent in the above slurry preparation step. Specifically, the water may be distilled water or deionized water. The use of water in the above slurry preparation step has the advantage of facilitating the formation of spherical granules during the spray drying step due to its high surface tension. Furthermore, conventional technology for manufacturing while maintaining the MgO powder state requires the use of organic solvents to maintain the MgO powder state within the slurry, which leads to problems such as volatilization and toxicity of the organic solvents. In contrast, since the present invention uses water as the solvent, the magnesium oxide precursor exists in the aqueous system in the form of Mg(OH)2 powder without dissociating significantly, which has the advantage of being stable and having high safety.

[0037] In order to manufacture a spherical magnesium oxide composite according to the present invention, it is necessary to form spherical granular particles through spray drying and then crystallize them by sintering. That is, in order to form spherical granular particles through spray drying, it is necessary for a magnesium oxide precursor (i.e., Mg(OH)2) to be stably dispersed in a particulate form within the slurry. To this end, the slurry includes a dispersant.

[0038] According to one embodiment of the present invention, the dispersant may be included in an amount of 0.5% to 5% by weight with respect to the solid content of the slurry. Specifically, the dispersant may be included in the slurry in an amount of 1% to 5% by weight, 1% to 4% by weight, 1.5% to 3.5% by weight, or 2% to 3% by weight. When the dispersant is included in the slurry within the above content range, magnesium oxide precursor particles can be dispersed with a high degree of dispersion within the slurry.

[0039] According to one embodiment of the present invention, the dispersant may be a water-soluble dispersant and may dissociate in an aqueous system to evenly disperse the magnesium oxide precursor. Specifically, the dispersant may include a carboxylate-based dispersant. More specifically, the dispersant may include at least one selected from the group consisting of polycarboxylate ammonium salt, polycarboxylate amine salt, polyacrylate sodium salt, polyacrylate calcium salt, polyacrylate potassium salt, and carboxymethylcellulose sodium salt. The dispersant may dissociate in an aqueous slurry to evenly disperse the magnesium oxide precursor, but anions derived from the dispersant may react with Mg₂ cations generated by the partial dissociation of the magnesium oxide precursor to form an insoluble salt. For example, if the above dispersant is a carboxylate-based dispersant, it dissolves in water to produce carboxylate anions, which react with Mg₂ cations dissociated from some magnesium oxide precursors to form an insoluble salt [Mg₂ 2+ + R-COO - → (R-COO)2Mg] This problem may occur. The formation of such insoluble salts can become more problematic when the slurry is mechanically ground to further finer the particles within the slurry. Specifically, this is because when the magnesium oxide precursor (i.e., Mg(OH)2 powder) is finely ground by mechanical grinding of the slurry and the degree of dissociation increases, an environment is created in which insoluble salts can be more easily formed by dissociated Mg2 cations and anions derived from the dispersant.

[0040] For example, if the above dispersant is an ammonium polycarboxylate salt, it can dissolve in an aqueous system and dissociate into a carboxylate anion and an ammonium cation [R-COOH·NH3↔ R-COO - + NH4 + (in aqueous)], at this time, the ammonium cation promotes the dissociation of Mg(OH)2 powder [Mg(OH)2(s) + NH4 +(aq) ↔ Mg 2 [(aq) + 2NH4OH(aq)], Mg₂ cations are generated, and a problem may arise in forming the aforementioned insoluble salt. The carboxylic acid anion lacks stability against Mg₂ cations, so it reacts with the cations dissociated from the slurry precursor to form insoluble salts and exists in the form of precipitates, which hinders the dispersibility of Mg(OH)₂ particles. To resolve this problem and improve the dispersibility of the magnesium oxide precursor in an aqueous system, a pH adjustment step using the pH adjuster described below is required. That is, the pH adjustment step described below allows the magnesium oxide precursor in the slurry to be evenly dispersed by the dispersant, thereby enabling the formation of homogeneous spherical granules through a spray drying step.

[0041] The above-mentioned inorganic additive is intended to provide a metal element other than magnesium to the spherical magnesium oxide composite, and the metal element derived from the above-mentioned inorganic additive may be substituted into the crystal structure of the magnesium oxide crystal grains through a sintering step to form a solid solution, or may form a metal oxide provided on the magnesium oxide crystal grains. The above-mentioned inorganic additive can significantly reduce the reactivity of the spherical magnesium oxide composite with moisture or substantially eliminate reactivity with moisture to provide moisture resistance, and can also ensure economic efficiency by lowering the sintering temperature during the sintering step.

[0042] According to one embodiment of the present invention, the inorganic additive may be selected from the group consisting of oxides, hydroxides, or carbonates comprising at least one selected from the group consisting of Ti, Nb, Zr, Ga, B, Fe, Sn, Mn, Si, V, Ta, Sb, Y, Eu, Er, Al, and Yb. Specifically, the inorganic additive may be an oxide of a metal selected from the group consisting of Ti, Nb, Zr, Ga, B, Fe, Sn, Mn, Si, V, Ta, Sb, Y, Eu, Er, Al, and Yb, or a combination of two or more metal oxides. More specifically, the inorganic additive may comprise at least one metal oxide selected from the group consisting of TiO2, Nb2O5, ZrO2, Ga2O3, Mn2O3, B2O3, Fe2O3, SnO2, MnO2, SiO2, V2O3, V2O5, Ta2O5, Sb2O5, Y2O3, Eu2O3, Er2O3, Al2O3, YbO, and Yb2O3.

[0043] According to one embodiment of the present invention, the inorganic additive may be included in the slurry in an amount of 0.01 mol to 0.3 mol per 1 mol of the magnesium precursor. Specifically, the inorganic additive may be included in the slurry in an amount of 0.01 mol to 0.2 mol, 0.05 mol to 0.2 mol, 0.07 mol to 0.2 mol, or 0.1 mol to 0.2 mol per 1 mol of the magnesium precursor. When the content of the inorganic additive is within the above range, the moisture resistance of the spherical magnesium oxide composite may be significantly improved, and furthermore, the sintering temperature during manufacturing may be lowered. In addition, if the content of the metal element is below the above range, the effect of improving the moisture resistance of the spherical magnesium oxide composite may not be sufficient, and if the content of the metal element exceeds the above range, the formation of crystal grains of the spherical magnesium oxide composite may be hindered due to the metal element or metal oxide.

[0044] According to one embodiment of the present invention, the solid content of the slurry may be 15 volume% to 45 volume%. Specifically, the solid content of the slurry may be 20 volume% to 40 volume%. When the solid content in the slurry is within the above range, spherical granule formation may be more easily achieved during the spray drying step. When the solid content of the slurry is below the above range, the moisture content in the slurry is excessively high, so granule formation may not be achieved well through the spray drying step. In addition, when the solid content of the slurry exceeds the above range, difficulties may arise in the spray drying process due to the increase in viscosity.

[0045] According to one embodiment of the present invention, the viscosity of the slurry may be 100 cPs to 2000 cPs. Specifically, the viscosity of the slurry may be 100 cPs to 1800 cPs, 100 cPs to 1800 cPs, 120 cPs to 1700 cPs, or 140 cPs to 1700 cPs. The viscosity of the slurry may be controlled by using the content of the solids, a dispersant, and a pH adjuster, taking into account the particle size of the desired spherical magnesium oxide composite. The viscosity may be measured by a spindle rotation method using a rotary viscometer (Anton Paar, viscoQC300) under conditions of room temperature (25 ℃) and 100 rpm.

[0046] According to one embodiment of the present invention, the slurry may further include a binder. The binder can be dissolved in water, which is a solvent, to control the viscosity of the slurry, and can strengthen the bonding force between particles during high-temperature drying after the formation of slurry droplets in the spray drying step, thereby enabling the formation of dense crystalline particles.

[0047] According to one embodiment of the present invention, the binder may be included in an amount of 0.05 wt% to 5 wt% with respect to the solid content of the slurry. Specifically, the binder may be included in the slurry in an amount of 0.05 wt% to 5 wt%, 0.05 wt% to 2 wt%, or 0.1 wt% to 1 wt%. When the content of the binder is within the above range, the spherical magnesium oxide composite can be formed into particles with dense crystal grains without cracks.

[0048] According to one embodiment of the present invention, the binder may comprise at least one selected from the group consisting of polyvinyl alcohol, polyvinylpyrrolidone, tributyl phosphate, polyethylene glycol, carboxymethyl cellulose, hydroxypropyl methylcellulose, and guar gum. More specifically, the binder may be polyvinyl alcohol.

[0049] pH adjustment step

[0050] The above pH adjustment step may be a step of adjusting the pH by adding a pH adjuster to the slurry to adjust the pH, thereby adjusting the physical properties of the slurry to be suitable for spray drying. Specifically, the above pH adjustment step may be adjusting the pH of the slurry to 9.9 to 10.5. More specifically, the above pH adjustment step may be adding a pH adjuster dropwise while measuring the pH of the slurry in real time using a pH meter.

[0051] As described above, the dispersant plays a role in increasing the dispersibility of the magnesium oxide precursor in the slurry, but a problem may arise in that it reacts with Mg₂ cations generated by the partial dissociation of the magnesium oxide precursor to form insoluble salts. The pH adjuster controls the dispersibility of the magnesium oxide precursor by controlling the pH of the slurry, thereby suppressing the dissociation reaction of the magnesium oxide precursor to allow it to exist stably within the slurry and preventing the formation of insoluble salts by the carboxylic acid-based dispersant. Specifically, the pH adjustment step can adjust the pH of the slurry to 9.9 to 10.5. If the pH of the slurry is less than 9.9, the formation of insoluble salts is not sufficiently prevented, which may cause the viscosity of the slurry to increase significantly. Consequently, it becomes difficult to perform the spray drying process, and problems may arise such as the formation of cracks or the formation of non-spherical, amorphous granules due to spray drying. In addition, if the pH of the above slurry exceeds 10.5, a problem may occur in which non-spherical, donut-shaped granules are formed by spray drying due to the excessively high pH.

[0052] The above pH adjuster may act as a viscosity control agent by directly affecting dispersibility. Furthermore, the above pH adjuster may play a role in stabilizing the viscosity within the slurry by adjusting the pH of the slurry to within the aforementioned range. Specifically, by adjusting the pH of the slurry to within the aforementioned range, the dissociation of magnesium oxide precursor particles within the slurry is prevented and their dispersibility is increased, thereby stabilizing the viscosity of the slurry.

[0053] According to one embodiment of the present invention, the pH adjuster may comprise at least one selected from the group consisting of ammonium hydroxide, ammonium carbonate, triethanolamine, monoethanolamine, urea, calcium hydroxide, potassium hydroxide, and sodium hydroxide. For example, when the pH adjuster is ammonium hydroxide, the dissociation reaction of the magnesium oxide precursor by the cation of the dispersant (e.g., [Mg(OH)2(s) + NH4 + (aq) ↔ Mg 2 It is also possible to induce the reverse reaction of (aq) + 2NH4OH(aq)]) so that Mg(OH)2 particles can be stably present in the aqueous slurry. Therefore, when the dispersant is an ammonium polycarboxylate salt, ammonium hydroxide may be more suitable as the pH adjuster. As described above, depending on the type of dispersant, the pH adjuster can be appropriately selected and applied to induce the reverse reaction of the dissociation reaction of the magnesium oxide precursor.

[0054] According to one embodiment of the present invention, the step of mechanically grinding the slurry may be further included. The mechanical grinding may utilize a ball mill, bead mill, hammer mill, roll crusher, jet mill, or finish mill, but is not limited thereto; any mechanical grinding method performed in the preparation of the slurry is applicable. Additionally, the mechanical grinding may be performed before adding the pH adjuster, after adding the pH adjuster, or simultaneously with adding the pH adjuster. Through the mechanical grinding, the particle size within the slurry can be homogenized and the dispersibility can be further improved.

[0055] Spray drying stage

[0056] The spray drying method in the above spray drying step may involve introducing the slurry into a spray dryer to form granular particles. Depending on the atomizing method, the spray drying method may be classified into a rotating type using the rotation of a disk or a nozzle type using an air nozzle. According to one embodiment of the present invention, the spray drying method may utilize a rotating spray drying method. In this case, the slurry is conveyed to a rotating disk, and droplets may be formed by the centrifugal force resulting from the high rotational speed of the disk. The droplets sprayed by the rotating spray drying method may be dried at a rapid speed by high-temperature hot air inside the chamber, which may be advantageous for forming spherical granules.

[0057] According to one embodiment of the present invention, the spray drying step may be performed under rotational speeds of 5,000 rpm to 15,000 rpm and temperature conditions of 110 ℃ to 300 ℃. Specifically, the rotational speed of the spray drying step may be 5,500 rpm to 15,000 rpm, 6,000 rpm to 14,000 rpm, 6,000 rpm to 13,000 rpm, 6,000 rpm to 12,000 rpm, or 6,500 rpm to 11,000 rpm. Additionally, the temperature range in the spray drying step may be 130 ℃ to 280 ℃, 150 ℃ to 270 ℃, 180 ℃ to 260 ℃, or 200 ℃ to 250 ℃. Within the above rotational speed range and temperature range, the formation of spherical granular particles can be predominantly controlled through spray drying. Specifically, by controlling within the above rotational speed range, the shape of the particles formed through spray drying can be formed into a spherical shape, and the particle size can be controlled to 10 μm to 300 μm. If the rotational speed and temperature range are exceeded, the formation of particles formed through spray drying may predominantly be amorphous particles, broken particles, or donut-shaped particles, which may not be desirable.

[0058] Sintering stage

[0059] The above sintering step may involve heating and crystallizing the granular particles formed through the above spray drying step.

[0060] According to one embodiment of the present invention, the sintering step may be performed within a sintering temperature range of 1,000 ℃ to 1,800 ℃. Specifically, the sintering temperature may be controlled according to the content of the inorganic additive. Depending on the content of the inorganic additive, the sintering temperature may be 1,200 ℃ to 1,800 ℃, 1,200 ℃ to 1,700 ℃, 1,200 ℃ to 1,600 ℃, or 1,250 ℃ to 1,550 ℃. The sintering temperature is significantly lower than the sintering temperature of general magnesium oxide, and since sintering is possible even at a lower sintering temperature due to increased diffusivity depending on the type and content of the additive, there is an advantage of excellent economic efficiency.

[0061] According to one embodiment of the present invention, after the sintering step, a step of separating and recovering the size of the spherical magnesium oxide composite may be further included. The separation and recovery step may utilize a sieving method, an air-flow classification method, a gravity classification method, or a centrifugal classification method.

[0062] Spherical magnesium oxide complex

[0063] Another embodiment of the present invention provides a spherical magnesium oxide composite produced by the above manufacturing method.

[0064] The spherical magnesium oxide composite may be formed by densely contacting magnesium oxide crystal grains. Specifically, the spherical magnesium oxide composite further comprises a metal element different from magnesium derived from an inorganic additive in a magnesium oxide-based matrix, and due to the presence of said metal element, the formation of magnesium hydroxide on the surface of the magnesium oxide caused by the absorption of moisture from the air can be significantly reduced or prevented. Through this, the spherical magnesium oxide composite can solve the problem of changes in physical properties caused by moisture absorption in general magnesium oxide. In addition, the spherical magnesium oxide composite may also have the advantage of lowering manufacturing costs by lowering the sintering temperature during production due to said metal element.

[0065] According to one embodiment of the present invention, the metal element may include at least one selected from the group consisting of Ti, Nb, Zr, Ga, B, Fe, Sn, Mn, Si, V, Ta, Sb, Y, Eu, Er, Al, and Yb. Specifically, the metal element may include at least one selected from the group consisting of Ti, Nb, Yb, and V.

[0066] The spherical magnesium oxide composite according to the present invention may be a sintered body having magnesium oxide containing the metal element as a base material, or a ceramic having magnesium oxide as a base material. Additionally, the spherical magnesium oxide composite according to the present invention may be a solid solution containing the metal element within the magnesium oxide crystal structure.

[0067] According to one embodiment of the present invention, the metal element may be provided by substituting it at the position of the magnesium element of the magnesium oxide crystal grain. More specifically, the metal element is Mg of the unit cell of the magnesium oxide crystal grain. 2+ At least a portion of it may be provided by being substituted with the above metal element.

[0068] According to one embodiment of the present invention, the metal element may be provided in the form of an oxide on the surface of the magnesium oxide crystal grains. Specifically, the metal element may be provided in the form of an oxide on the interface and / or surface of the magnesium oxide crystal grains. More specifically, the metal oxide may exist as another phase at the magnesium oxide grain boundaries. In this case, the metal oxide may be irregularly present on the surface of the spherical magnesium oxide composite.

[0069] According to one embodiment of the present invention, the metal element may be provided by substituting it at the magnesium element position of the magnesium oxide crystal grain, and at the same time, may be provided in the form of a metal oxide on the surface of the magnesium oxide crystal grain.

[0070] According to one embodiment of the present invention, the content of the metal element may be 0.02 at.% or more and 6 at.% or less with respect to the magnesium element (with respect to 100 at.% of the Mg element). Specifically, the content of the metal element may be 0.02 at.% or more and 5 at.% or less, 0.02 at.% or more and 4 at.% or less, 0.02 at.% or more and 3 at.% or less, 0.02 at.% or more and 2 at.% or less, 0.04 at.% or more and 2 at.% or less, 0.04 at.% or more and 0.4 at.% or less, 0.1 at.% or more and 2 at.% or less, 0.09 at.% or more and 0.5 at.% or less, or 0.1 at.% or more and 0.4 at.% or less with respect to the magnesium element. When the content of the metal element is within the above range, the moisture resistance of the spherical magnesium oxide composite can be significantly improved, and furthermore, the sintering temperature during manufacturing can be lowered. In addition, if the content of the metal element is below the above range, the effect of improving the moisture resistance of the spherical magnesium oxide composite may not be sufficient, and if the content of the metal element exceeds the above range, the metal element or metal oxide may interfere with the formation of crystal grains of the spherical magnesium oxide composite.

[0071] The content of the above metal element can be determined by methods known in the industry, for example, through EDS, WDS, EPMA, XRF, or Rietveld refinement of neutron and X-ray diffraction, and can also be determined through ICP analysis.

[0072] According to one embodiment of the present invention, the particle size of the spherical magnesium oxide composite may be in the range of 10 μm to 300 μm. Specifically, the particle size of the spherical magnesium oxide composite may be 10 μm to 250 μm, 10 μm to 200 μm, or 10 μm to 150 μm. The particle size may refer to the average particle size of the particles.

[0073] According to one embodiment of the present invention, the spherical magnesium oxide composite may have a sphericity of 90% or more. The sphericity refers to a degree of sphericity that can be confirmed as spherical through SEM images, etc., and does not mean a shape with 100% sphericity.

[0074] According to one embodiment of the present invention, the spherical magnesium oxide composite may have a weight gain rate of less than 1% after a moisture resistance test for 72 hours under an atmosphere of 85°C and 85%RH. Specifically, the spherical magnesium oxide composite may have a weight gain rate of less than 0.7% or 0.5% or less after a moisture resistance test for 72 hours under an atmosphere of 85°C and 85%RH. The weight gain rate of conventional magnesium oxide in the moisture resistance test results was generally over 10%, and even when the sintering temperature was increased, the weight gain rate exceeded 1%. In contrast, the spherical magnesium oxide composite according to the present invention exhibits significantly improved moisture resistance results compared to conventional magnesium oxide.

[0075] Hereinafter, the present invention will be described in detail with reference to examples to specifically explain the invention. However, the embodiments according to the present invention may be modified in various different forms, and the scope of the present invention is not to be interpreted as being limited to the embodiments described below. The embodiments of this specification are provided to more completely explain the present invention to those with average knowledge in the art.

[0076] [Examples 1 to 10]

[0077] A slurry was prepared by adding Mg(OH)2 powder as a magnesium oxide precursor, 0.0345 mol% (0.23 wt%) of Nb2O5 per 1 mol (100 wt%) of Mg(OH)2 as inorganic additives, 0.135 mol% (0.27 wt%) of TiO2 per 1 mol (100 wt%) of Mg(OH)2 as inorganic additives, ammonium polycarboxylate salts in the amounts shown in Table 1 below, and 0.5 wt% of polyvinyl alcohol relative to the solid content as a binder to distilled water and stirring. The slurry was further mixed and ground using a ball mill with ZrO2 beads, and the pH of the slurry was adjusted as shown in Table 1 below by adding ammonium hydroxide dropwise while monitoring the pH of the slurry in real time using a pH meter (Metler toledo, SD20).

[0078] Then, the atomizer rotation speed was set to approximately 8,000 rpm and the drying temperature to 215 ℃, and granulation was performed using the spray drying method. Then, the granulated particles were sintered at a temperature of approximately 1,450 ℃ for approximately 2 hours to produce sintered particles. The particle size of the produced sintered particles was measured using a Laser Particle Size Analyzer (Horiba, LA960V2), and the sphericity was evaluated using an SEM image (Hitachi high tech, TM4000II) as the average value of the ratio of the lengths perpendicular to the major and minor axes for more than 15 sintered particles, and is listed in Table 1 below.

[0079] [Comparative Examples 1 to 2]

[0080] Sintered particles were prepared in the same manner as in the example, except that citric acid was used instead of ammonium hydroxide as a pH adjuster to adjust the pH of the slurry as shown in Table 1 below.

[0081] [Comparative Example 3]

[0082] Sintered particles were prepared in the same manner as in the example without applying a pH adjuster.

[0083] [Comparative Examples 4 to 5]

[0084] Sintered particles were prepared in the same manner as in the example, except that ammonium hydroxide was added dropwise to raise the pH of the slurry to greater than 10.5 as shown in Table 1 below.

[0085] Slurry After Spray Drying After Sintering Treatment Solids (vol%) Dispersant (wt%) relative to solids pH Viscosity (cPs) Spray Drying Process Granule Shape Particle Size Range (㎛) Sphericity (%) Comparative Example 1 30 2.5 9.0 4,260 Clogging during spraying Cracking -- Comparative Example 2 30 2.5 9.5 2,170 Clogging during spraying Cracking -- Comparative Example 3 30 2.5 9.8 1,440 Clogging during spraying Amorphous 30 -260 84.8 Example 1 30 2.5 9.9 1,200 Suitable Spherical 40 -260 90.7 Example 2 30 2.5 9.9 1,000 Suitable Spherical 50 -260 92.7 Example 3302.510.07700 Suitable spherical shape 70-23093.1 Example 4302.510.16550 Suitable spherical shape 60-26093.8 Example 5302.510.33300 Suitable spherical shape 50-26093.2 Example 6302.510.49180 Suitable spherical shape 40-26092.1 Comparative Example 4302.510.63100 Donut with difficulty in uniform spraying--Comparative Example 5302.511.0470 Donut with difficulty in uniform spraying--Example 7202.510.095 Suitable spherical shape 20-26090.6 Example 8252.510.0600 Suitable spherical shape 30-26091.7 Example 9352.510.36450 Suitable Spherical Form 60-23092.8 Example 10402.510.32600 Suitable Spherical Form 60-23092.6

[0086] Figure 1 is a graph showing the trend of sphericity of sintered particles according to the pH of the slurry for each solid content of various slurries, based on the composition of the example. As can be seen in Figure 1, it was confirmed that the sphericity of the sintered particles can be controlled to 90% or more through pH control, as long as the solid content of the slurry does not affect the spray drying process.

[0087] Figure 2 shows an SEM image of sintered particles prepared according to Comparative Example 1. Figure 3 shows an SEM image of sintered particles prepared according to Comparative Example 2. Figure 4 shows an SEM image of sintered particles prepared according to Comparative Example 3. Referring to Figures 2 to 4, it was confirmed that when the pH of the slurry is adjusted to less than 9.9, unlike the present invention, severe cracks are formed in the particles, or non-spherical amorphous particles are formed.

[0088] Figure 5 shows an SEM image of sintered particles prepared according to Example 2. Figure 6 shows an SEM image of sintered particles prepared according to Example 4. Figure 7 shows an SEM image of sintered particles prepared according to Example 6. Figure 8 shows an SEM image of sintered particles prepared according to Example 9. Figure 9 shows an SEM image of sintered particles prepared according to Example 10. Referring to Figures 5 to 9, it was confirmed that when the pH of the slurry is adjusted to 9.9 to 10.5 as in the present invention, most of the sintered particles are manufactured in a spherical shape. Furthermore, referring to Figure 7, it was confirmed that metal elements derived from inorganic additives are distributed between MgO crystal grains and / or on the surface of the crystal grains, and such magnesium oxide composites can have significantly improved moisture resistance as described in the experimental examples below.

[0089] Figure 10 shows an SEM image of sintered particles prepared according to Comparative Example 4. Figure 11 shows an SEM image of sintered particles prepared according to Comparative Example 5. Referring to Figures 10 and 11, it was confirmed that when the pH of the slurry is adjusted to be greater than 10.5, unlike the present invention, donut-shaped and amorphous particles, rather than spherical particles, are mainly produced.

[0090] In addition, to evaluate the hygroscopicity of the sintered particles prepared according to the example, a hygroscopicity test was performed on the sintered particles prepared according to Example 4. Specifically, the weight gain rate of the sintered particles prepared according to Example 4 was measured after being left for 72 hours under an atmosphere of 85°C and 85%RH, and the measurement results confirmed that the weight gain rate was only 0.37%. To confirm this, XRD analysis was performed before and after the 72-hour test under 85°C and 85%RH, as shown in the results of Figure 12. According to Figure 12, it was confirmed that after the hygroscopicity test, no magnesium hydroxide phase resulting from moisture absorption was detected in the sintered particles, and the magnesium oxide phase was maintained almost identically to before the test.

Claims

1. A slurry preparation step of forming a slurry by mixing a magnesium oxide precursor comprising at least one of Mg(OH)2 powder and MgO powder, an inorganic additive, a dispersant, and water; A pH adjustment step of adjusting the pH of the slurry using a pH adjuster; A spray drying step of preparing the above slurry into granular powder using a spray drying method; and A sintering step comprising crystallizing the above granular powder by sintering treatment; Method for manufacturing a spherical magnesium oxide complex.

2. In Claim 1, A method for manufacturing a spherical magnesium oxide composite, wherein the pH adjustment step is to adjust the pH of the slurry to 9.9 to 10.

5.

3. In Claim 1, A method for manufacturing a spherical magnesium oxide composite, wherein the solid content of the slurry is 15 volume% to 45 volume%.

4. In Claim 1, A method for manufacturing a spherical magnesium oxide composite, wherein the above-mentioned inorganic additive is selected from the group consisting of oxides, hydroxides, or carbonates comprising at least one selected from the group consisting of Ti, Nb, Zr, Ga, B, Fe, Sn, Mn, Si, V, Ta, Sb, Y, Eu, Er, Al, and Yb.

5. In Claim 1, A method for manufacturing a spherical magnesium oxide composite, wherein the above-mentioned inorganic additive is included in the slurry in an amount of 0.01 mol to 0.3 mol per 1 mol of the magnesium precursor.

6. In Claim 1, A method for manufacturing a spherical magnesium oxide composite, wherein the above-mentioned dispersant comprises a carboxylate-based dispersant.

7. In Claim 6, A method for manufacturing a spherical magnesium oxide composite, wherein the above-mentioned dispersant comprises at least one selected from the group consisting of polycarboxylate ammonium salt, polycarboxylate amine salt, polyacrylate sodium salt, polyacrylate calcium salt, polyacrylate potassium salt, and carboxymethylcellulose sodium salt.

8. In Claim 1, A method for manufacturing a spherical magnesium oxide composite, wherein the above-mentioned dispersant is included in an amount of 0.5% to 5% by weight relative to the solid content of the slurry.

9. In Claim 1, A method for manufacturing a spherical magnesium oxide complex, wherein the above pH adjuster comprises at least one selected from the group consisting of ammonium hydroxide, ammonium carbonate, triethanolamine, monoethanolamine, urea, calcium hydroxide, potassium hydroxide, and sodium hydroxide.

10. In Claim 1, A method for manufacturing a spherical magnesium oxide composite, wherein the above slurry further comprises a binder.

11. In Claim 10, A method for manufacturing a spherical magnesium oxide composite, wherein the binder comprises at least one selected from the group consisting of polyvinyl alcohol, polyvinylpyrrolidone, tributyl phosphate, polyethylene glycol, carboxymethyl cellulose, hydroxypropyl methylcellulose, and guar gum.

12. In Claim 10, A method for manufacturing a spherical magnesium oxide composite, wherein the binder is included in an amount of 0.05 weight% to 5 weight% with respect to the solid content of the slurry.

13. In Claim 1, A method for manufacturing a spherical magnesium oxide composite, wherein the above spray drying step is performed under rotational speeds of 5,000 rpm to 15,000 rpm and temperature conditions of 110 ℃ to 300 ℃.

14. In Claim 1, A method for manufacturing a spherical magnesium oxide composite, wherein the above sintering step is performed within a sintering temperature range of 1,000 ℃ to 1,800 ℃.

15. In Claim 1, A method for manufacturing a spherical magnesium oxide composite, wherein the particle size of the spherical magnesium oxide composite is within the range of 10 μm to 300 μm.

16. In Claim 1, A method for manufacturing a spherical magnesium oxide composite, wherein the spherical magnesium oxide composite has a sphericity of 90% or more.

17. Spherical magnesium oxide composite manufactured by the manufacturing method according to Claim 1.

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