WO2024204485A1 - Spherical magnesium oxide, production method for same, thermally conductive filler, and resin composition - Google Patents

Abstract

The purpose of the present invention is to provide: spherical magnesium oxide that high sphericity and excellent filling properties with respect to resin, and that exhibits little increase in viscosity when kneaded with resin; and a production method for the same.　The present invention is spherical magnesium oxide comprising 0.05-2.0% titanium and 100-1,500 ppm iron, wherein volume-based cumulative 50% particle diameter (D50) as found by laser diffraction particle size distribution measurement is in the range of 3-200 μm, and sphericity as observed from an SEM image is 1.00-1.20.

Description

Spherical magnesium oxide, its manufacturing method, thermally conductive filler, and resin composition

The present invention relates to spherical magnesium oxide and a method for producing the same, as well as a thermally conductive filler containing the spherical magnesium oxide and a resin composition containing the same.

Silica, alumina, etc. have traditionally been used as thermally conductive fillers, but silica has low thermal conductivity and is insufficient at dissipating heat to cope with the increase in heat generated by recent trends such as high integration, high power consumption, and high speed, which can cause problems with the stable operation of semiconductors. On the other hand, alumina has a higher thermal conductivity than silica, and improves heat dissipation compared to silica, but alumina's high hardness causes severe wear on kneading machines, molding machines, molds, etc., which is a problem. For this reason, magnesium oxide, which has a thermal conductivity one order of magnitude higher than silica and about twice that of alumina, and is also less hard than alumina, and can suppress wear on each manufacturing equipment, is being considered as a thermally conductive filler.

Various technological developments have been made to obtain magnesium oxide that is more suitable as a thermally conductive filler. Patent Document 1 proposes magnesium oxide in which a boron compound or the like is added to control the aggregation state and particle size distribution. Patent Document 2 proposes spherical magnesium oxide with a smooth and dense surface, which is obtained by adding a lithium compound. Patent Document 3 proposes spherical magnesium oxide with excellent moisture resistance and filling properties, which is obtained by adjusting the boron and iron content within a certain range.

JP 2011-020870 A JP 2016-088838 A JP 2018-131378 A

As shown in Patent Documents 1 to 3, conventionally, the main objective of technological development for magnesium oxide as a thermally conductive filler has been to improve the filling ability. On the other hand, there has also been hope for an improvement in the increase in viscosity that occurs when the filler is filled into a resin, to facilitate resin processing, but technological development from this perspective has not been sufficient to date. Therefore, the objective of the present invention is to provide spherical magnesium oxide that has high sphericity, excellent filling ability into resin, and small increase in viscosity when kneaded into resin, and a method for producing the same.

In order to solve the above problems, the inventors conducted extensive research and discovered that by adjusting the titanium and iron content within a certain range, it is possible to obtain spherical magnesium oxide that has high sphericity, excellent fillability into resin, and small increase in viscosity when filled into resin, and thus completed the present invention. The gist of the present invention is as follows.

[1] Spherical magnesium oxide containing 0.05 to 2.0% titanium and 100 to 1,500 ppm iron, having a volume-based cumulative 50% particle size (D ₅₀ ) in the range of 3 to 200 μm as measured by laser diffraction/scattering particle size distribution measurement, and having a sphericity of 1.00 to 1.20 as measured by SEM photography.

[2] The spherical magnesium oxide of [1], having a cumulative 50% particle diameter (D ₅₀ ) of more than 25 μm and not more than 150 μm.

[3] A thermally conductive filler containing spherical magnesium oxide of [1] or [2].

[4] A resin composition containing the thermally conductive filler of [3].

[5] A method for producing spherical magnesium oxide, comprising the steps of: 1) reacting an aqueous magnesium chloride solution with an aqueous alkali solution to prepare a magnesium hydroxide slurry; 2) drying and calcining the magnesium hydroxide slurry to prepare magnesium oxide; 3) dispersing the magnesium oxide in a solvent to prepare a dispersion, followed by wet-grinding; 4) spray-drying the magnesium oxide dispersion after wet-grinding; and 5) calcining the spherical magnesium oxide granulated by spray-drying, wherein in at least one of steps 1) to 5), the titanium and/or iron content is adjusted so that the spherical magnesium oxide after calcination has a titanium content of 0.05 to 2.0% and an iron content of 100 to 1,500 ppm.

Note that any two or more of the configurations [1] to [5] above can be selected and combined.

The present invention provides spherical magnesium oxide with high sphericity, excellent fillability into resin, and small increase in viscosity when filled into resin, as well as a method for producing the same.

The spherical magnesium oxide of the present invention contains 0.05 to 2.0% titanium and 100 to 1,500 ppm iron, has a volume-based cumulative 50% particle size (D ₅₀ ) in the range of 3 to 200 μm as measured by laser diffraction scattering particle size distribution measurement, and has a sphericity of 1.00 to 1.20 as read from a SEM photograph. In the description of the contents in the specification, % means % by mass, and ppm means ppm by mass, unless otherwise specified. The spherical magnesium oxide of the present invention is intended to be magnesium oxide powder.

First, the spherical magnesium oxide obtained in the present invention has a volume-based cumulative 50% particle size ( _D50 ) measured by laser diffraction/scattering particle size distribution measurement of 3 to 200 μm, preferably 15 to 180 μm, and more preferably more than 25 μm and not more than 150 μm, which is a relatively large particle size range capable of improving heat dissipation performance, and also has high sphericity and excellent filling ability.

In the present invention, sphericity refers to the sphericity that can be read from a scanning electron microscope (SEM) photograph, and should be 1.00 to 1.20, preferably 1.00 to 1.15, and more preferably 1.00 to 1.10. Such sphericity provides excellent filling properties into resin. In the present invention, the lengths of the major and minor axes passing through the center of the particles are measured for 100 particles in an electron microscope photograph taken using an SEM, the ratio of the major axis to the minor axis is calculated, and the average value is taken as the sphericity.

In the present invention, by adjusting the titanium and iron contents of the spherical magnesium oxide within a certain range, it is possible to obtain spherical magnesium oxide with high sphericity and small viscosity increase when filled with resin. Here, the titanium content is 0.05 to 2.0%, preferably 0.08 to 1.5%, and more preferably 0.1 to 1.0%. At the same time, the iron content is 100 to 1,500 ppm, preferably 150 to 1,300 ppm, and more preferably 200 to 1,000 ppm. By mixing the titanium and iron contents in appropriate amounts and in a balanced manner, spherical magnesium oxide with high sphericity and small viscosity increase when filled with resin can be obtained.

The method for producing spherical magnesium oxide of the present invention is not particularly limited, but can be produced, for example, by the following production method: 1) a step of reacting an aqueous magnesium chloride solution with an aqueous alkali solution to prepare magnesium hydroxide slurry, 2) a step of drying and firing the magnesium hydroxide slurry to prepare magnesium oxide, 3) a step of dispersing the magnesium oxide in a solvent to prepare a dispersion liquid, which is then wet-pulverized, 4) a step of spray-drying the magnesium oxide dispersion liquid after wet-pulverization, and 5) a step of firing the spherical magnesium oxide granulated by spray drying, and in at least one or more of the steps 1) to 5), the titanium and/or iron content is adjusted so that the titanium content in the spherical magnesium oxide after firing is 0.05 to 2.0% and the iron content is 100 to 1,500 ppm.

More specifically, the above-mentioned production method can be carried out as follows.
1) A magnesium chloride aqueous solution is reacted with an alkaline aqueous solution to obtain a magnesium hydroxide slurry, and then
2) The slurry is filtered, washed with water, dried, and then calcined to obtain magnesium oxide.
3) The magnesium oxide is dispersed in a solvent, preferably an organic solvent, to obtain a dispersion liquid, which is then wet-pulverized.
4) Spray drying is carried out;
5) The obtained spherical magnesium oxide is fired to obtain the desired spherical magnesium oxide. At this time, a titanium source and/or an iron source are mixed and/or added before the final firing so that the titanium content of the spherical magnesium oxide after the final firing is 0.05 to 2.0% and the iron content is 100 to 1,500 ppm. Specifically, the titanium content and/or the iron source are adjusted by, for example, a) adding a boron source and/or an iron source to an aqueous magnesium chloride solution and/or an alkaline aqueous solution, b) adding a titanium source and/or an iron source to the generated magnesium hydroxide slurry, c) mixing a titanium source and/or an iron source with magnesium oxide obtained by firing magnesium hydroxide, d) adding a titanium source and/or an iron source during wet grinding of magnesium oxide, e) mixing a titanium source and/or an iron source with spherical magnesium oxide granulated by spray drying, or the like, to adjust the titanium content and iron content in the spherical magnesium oxide finally obtained. The titanium content and the iron content may be adjusted in the same process or in different processes.

The titanium source is not particularly limited as long as it is a compound containing titanium, but examples include titanium oxide (anatase type, rutile type), titanium chloride, titanium hydroxide, titanium bromide, titanium fluoride, magnesium titanate, etc.

The iron source is not particularly limited as long as it is a compound containing iron, but examples include iron oxide (II), iron oxide (III), iron tetroxide, iron hydroxide, iron chloride, iron nitride, iron bromide, and iron fluoride.

The titanium source is adjusted so that the titanium content of the spherical magnesium oxide after final firing is 0.05-2.0%. If the titanium content is less than 0.05%, the effect of reducing viscosity is not sufficient. Furthermore, if the titanium content exceeds 2.0%, excessive particle growth and adhesion between particles are likely to occur, making it impossible to obtain spherical magnesium oxide with high sphericity. Then, the iron source is adjusted so that the iron content of the spherical magnesium oxide after final firing is 100-1,500 ppm. In addition to the above titanium content, if the iron content is in the range of 100-1,500 ppm, spherical magnesium oxide with high sphericity tends to be obtained.

The magnesium chloride aqueous solution can be selected from, for example, magnesium chloride hexahydrate, magnesium chloride dihydrate, anhydrous magnesium chloride, bittern, seawater, and combinations thereof.

The alkaline aqueous solution can be selected from, for example, an aqueous sodium hydroxide solution, an aqueous calcium hydroxide solution, ammonia water, and combinations thereof.

The magnesium hydroxide slurry obtained by reacting an aqueous magnesium chloride solution with an aqueous alkali solution is filtered, washed with water, dried, and then calcined to form magnesium oxide, for example, by a method common in the technical field. The obtained magnesium oxide is then dispersed in a solvent to form a dispersion (for example, a slurry), which is wet-pulverized and spray-dried to form granules. The solvent used here is not particularly limited, but any known solvent can be used, such as water-based systems, water-organic solvent mixtures, alcohols such as methanol and ethanol, ketones such as acetone, esters such as ethyl acetate, ethers such as diethyl ether, and aromatic compound solvents such as tetrahydrofuran and toluene.

The method of spray drying is not particularly limited, but it is preferable to use a spray drying method in which a magnesium oxide dispersion (e.g., a slurry) after wet grinding is sprayed from a rotating disk or nozzle to obtain magnesium oxide particles. The operating conditions are appropriately adjusted according to the slurry viscosity, the particle size of the powder in the slurry, the target particle size, and the like. In addition, a dispersant may be appropriately added to the slurry. The operating conditions are not particularly limited, but in the case of the spray drying method, for example, a slurry with a viscosity adjusted to 10 to 3000 cps is sprayed from a rotating disk or nozzle into an air flow at 80°C to 250°C by appropriately adjusting the flow rate, and particles of about 1 to 200 μm can be produced. In addition, it is preferable to adjust the concentration of the dispersion during wet grinding and spraying so that, for example, magnesium oxide is 50 to 70 wt %. Here, by appropriately setting the spray conditions, the sphericity of the obtained spherical magnesium oxide can be adjusted. In addition, by appropriately setting the spray conditions, the cumulative 50% particle size (D ₅₀ ) of the obtained spherical magnesium oxide can be adjusted. The spray drying method is preferred since it can stably obtain particles having a large particle size.

The conditions for sintering the granulated magnesium oxide are not particularly limited as long as they are within the range in which the magnesium oxide particles are sintered, but a temperature of 1000°C to 1800°C is preferable, 1100°C to 1700°C is more preferable, and 1200°C to 1600°C is particularly preferable. The sintering time depends on the sintering temperature, but is preferably 0.5 to 10 hours. If the sintering temperature is less than 1000°C, sufficient sintering will not occur, and if it exceeds 1800°C, the particles will sinter together and form coarse agglomerates, so it is adjusted to the above range.

The spherical magnesium oxide of the present invention can also be surface-treated using a known method for the purpose of improving moisture resistance. When surface-treating the spherical magnesium oxide of the present invention, there are no particular limitations on the surface treatment agent used, but examples that can be used include colloidal silica, silane-based coupling agents, titania sol, titanate-based coupling agents, phosphorus compounds, alumina sol, aluminate-based coupling agents, zirconium-based coupling agents, etc. These may be used alone or in combination of two or more types.

Examples of silane coupling agents include vinyltrichlorosilane, vinyltrialkoxysilane, glycidoxypropyltrialkoxysilane, and methacryloxypropylmethyldialkoxysilane.

Titanate coupling agents include, for example, tetraisopropyl titanate, tetranormalbutyl titanate, tetraoctyl titanate, tetrastearyl titanate, isopropyltriisostearoyl titanate, tetraoctylbis(ditridecylphosphite)titanate, bis(dioctylpyrophosphate)oxyacetate titanate, etc.

The phosphorus compound is not particularly limited as long as it is a compound that can react with magnesium oxide to form a magnesium phosphate compound, but examples include phosphoric acid, phosphates, and acidic phosphate esters. Examples of acidic phosphate esters include isopropyl acid phosphate, 2-ethylhexyl acid phosphate, oleyl acid phosphate, methyl acid phosphate, ethyl acid phosphate, propyl acid phosphate, butyl acid phosphate, lauryl acid phosphate, and stearyl acid phosphate.

Examples of aluminate coupling agents include aluminum isopropylate, monosec-butoxyaluminum diisopropylate, aluminum sec-butylate, aluminum ethyl acetoacetate diisopropylate, aluminum tris(ethyl acetoacetate), and aluminum alkyl acetoacetate diisopropylate.

Examples of zirconium-based coupling agents include normal propyl zirconate and normal butyl zirconate.

The spherical magnesium oxide of the present invention has the advantages of high sphericity, excellent filling properties, and small increase in viscosity when filled into resin, and can therefore be suitably blended into resin as a filler, making it useful as a thermally conductive filler. The thermally conductive filler of the present invention may contain the spherical magnesium oxide of the present invention alone, or may contain the spherical magnesium oxide of the present invention together with other thermally conductive filler materials. The resin composition of the present invention contains the thermally conductive filler of the present invention, and examples of resins that can be used in the present invention include thermosetting resins and thermoplastic resins. Thermosetting resins are not particularly limited, but examples include phenolic resins, urea resins, melamine resins, alkyd resins, polyester resins, epoxy resins, diallyl phthalate resins, polyurethane resins, and silicone resins. Thermoplastic resins are not particularly limited, but examples include polyamide resins, polyacetal resins, polycarbonate resins, polybutylene terephthalate resins, polyolefin resins, polysulfone resins, polyamideimide resins, polyetherimide resins, polyarylate resins, polyphenylene sulfide resins, polyether ether ketone resins, fluororesins, and liquid crystal polymers.

The amount of spherical magnesium oxide in the resin composition of the present invention may be appropriately determined depending on the properties required of the resin composition, and is not particularly limited. However, as an example, spherical magnesium oxide may be used in the range of 0.1 to 100 parts by mass per 100 parts by mass of resin.

The resin composition containing the spherical magnesium oxide of the present invention can be used in various fields depending on the characteristics of the resin. However, since the spherical magnesium oxide of the present invention has excellent thermal conductivity, it can be used particularly preferably in applications where heat dissipation is required. For example, the resin composition of the present invention can be used as a semiconductor encapsulation material with excellent thermal conductivity.

The present invention will be described in detail with reference to the following examples, but these examples are not intended to limit the present invention in any way.

[Measurement and evaluation methods]
(1) Measurement method of iron content The iron content was measured by ICP emission spectrometry. The measurement sample was added to 12N hydrochloric acid (special grade reagent) and heated to completely dissolve, and the iron content was measured using an ICP measurement device (PS3520 VDD, manufactured by Hitachi High-Tech Science Corporation).

(2) Measurement method of titanium content The titanium content was measured using an X-ray fluorescence analyzer (device name: ZSX Primus4, manufactured by Rigaku Corporation). First, the magnesium oxide to be measured was placed in an aluminum ring (φ35 mm), sandwiched between dies, and pelletized using a press (surface pressure 250 MPa) to obtain a measurement sample. This sample was measured in SQX analysis (EZ scan) mode (bulb: Rh (4 kW), atmosphere: vacuum, analysis window: Be (30 μm), measurement diameter: 30 mmφ, measurement range F to U) to determine the titanium content in the magnesium oxide.

(3) Volume-based cumulative 50% particle size ( _D50 )
0.1×10 ⁻³ kg of the measurement sample was precisely weighed, dispersed in 40 mL of methanol, and measured using a laser diffraction scattering type particle size distribution measuring device (MT3300, manufactured by Nikkiso Co., Ltd.).

(4) Sphericity as seen from SEM photographs Magnesium oxide samples were photographed using a scanning electron microscope (SEM) (JSM6510LA, manufactured by JEOL Ltd.) The major and minor axes passing through the center of the particles were measured for 100 randomly selected particles in the electron microscope photographs, and the ratio of the major axis to the minor axis was calculated, and the average value was taken as the sphericity.

(5) Viscosity evaluation during resin filling Spherical magnesium oxide to be evaluated and alumina particles (Denka's "DAW-05" (average particle size: 5 μm)) were mixed at 50% by volume, and this was added to silicone oil (Shin-Etsu Chemical's "KF96-100cs") so that the total filling rate of the spherical magnesium oxide and alumina particles was 75% by volume. This was mixed for 30 seconds at a rotation speed of 2,200 rpm using a rotation/revolution mixer, and then vacuum degassed to obtain a resin composition. The viscosity of the obtained resin composition was measured using a B-type viscometer (TOKIMEC's BL type, measurement conditions: sample temperature 25°C, 6 rpm, rotor No. 4, container dimensions φ26 mm × h46 mm, sample amount 20 mL).

[Examples and Comparative Examples]
Example 1
Anhydrous magnesium chloride (MgCl ₂ ) was dissolved in ion-exchanged water to prepare an aqueous magnesium chloride solution of about 3.5 mol/l. The MgCl ₂ solution and 25% NaOH solution were each pumped into a reactor with a metering pump so that the reaction rate of MgCl ₂ was 90 mol%, and a continuous reaction was carried out to obtain a magnesium hydroxide slurry. Then, titanium oxide/anatase type (manufactured by Teika Co., Ltd., JA-20) was added to the magnesium hydroxide slurry so that the titanium content in the spherical magnesium oxide finally obtained was 0.7%, and iron oxide (II) (manufactured by Hayashi Pure Chemical Industries Co., Ltd.) was added so that the iron content was 250 ppm. Then, the mixture was filtered, washed with water, and dried to obtain magnesium hydroxide. The obtained magnesium hydroxide was fired at 900°C for 1 hour to obtain magnesium oxide. The obtained magnesium oxide was dispersed in an organic solvent to obtain a slurry with a magnesium oxide concentration of 65 wt%. Then, wet grinding was performed using a ball mill for 4 hours, and spray drying was performed by a spray drying method. The resulting spray-dried spherical magnesium oxide was finally fired in an electric furnace at 1400° C. for 1 hour to obtain the desired spherical magnesium oxide.

Example 2
Spherical magnesium oxide was obtained using the same production method as in Example 1, except that titanium oxide was added to the reaction liquid so that the titanium content in the spherical magnesium oxide was 0.39% and iron (II) oxide was added to the reaction liquid so that the iron content was 330 ppm.

Example 3
Spherical magnesium oxide was obtained using the same production method as in Example 1, except that titanium oxide was added to the reaction liquid so that the titanium content in the spherical magnesium oxide was 0.11% and iron (II) oxide was added to the reaction liquid so that the iron content was 330 ppm.

Example 4
Spherical magnesium oxide was obtained using the same manufacturing method as in Example 1, except that titanium oxide was added to the reaction solution so that the titanium content in the spherical magnesium oxide was 0.75% and iron (II) oxide was added so that the iron content was 240 ppm, and the firing temperature in the final firing was 1300°C.

(Comparative Example 1)
Spherical magnesium oxide was obtained in the same manner as in Example 1, except that no titanium source was added to the reaction solution, and iron (II) oxide was added so that the iron content was 240 ppm.

The above measurements and evaluations were carried out for Examples 1 to 4 and Comparative Example 1. The results are shown in Table 1.

As is clear from Table 1, the spherical magnesium oxide of Examples 1 to 4 had high sphericity and the increase in viscosity when filled with resin was kept low. On the other hand, the spherical magnesium oxide of Comparative Example 1 had high sphericity, but the increase in viscosity when filled with resin was large, and its performance as a filler was poor.

From this, it was found that the spherical magnesium oxide of the present invention has a small increase in viscosity when filled into resin, has high sphericity, and is excellent in fillability into resin. Therefore, it was found that the spherical magnesium oxide of the present invention is useful as an excellent resin filler.

The present invention provides spherical magnesium oxide that exhibits a small increase in viscosity when filled into resin, has high sphericity, and is excellent in fillability into resin, as well as a method for producing the same.

Claims (5)

The present invention relates to a spherical magnesium oxide having a volume-based cumulative 50% particle size (D ₅₀ ) in the range of 3 to 200 μm as measured by a laser diffraction/scattering particle size distribution measurement, and a sphericity of 1.00 to 1.20 as measured by a SEM photograph. The spherical magnesium oxide according to claim 1, having a cumulative 50% particle size (D ₅₀ ) of more than 25 μm and not more than 150 μm. A thermally conductive filler containing the spherical magnesium oxide according to claim 1 or 2. A resin composition containing the thermally conductive filler according to claim 3. 1) reacting an aqueous magnesium chloride solution with an aqueous alkali solution to prepare a magnesium hydroxide slurry;
2) drying and calcining the magnesium hydroxide slurry to prepare magnesium oxide;
3) dispersing the magnesium oxide in a solvent to obtain a dispersion liquid, and then wet-grinding the dispersion liquid;
4) spray-drying the magnesium oxide dispersion after wet grinding;
5) Calcining the spherical magnesium oxide granulated by spray drying;
Including,
In at least one of the steps 1) to 5), the titanium and/or iron content is adjusted so that the titanium content in the spherical magnesium oxide after firing is 0.05 to 2.0% and the iron content is 100 to 1,500 ppm.
A method for producing spherical magnesium oxide.