JP2014136654A - Coated magnesium oxide powder and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coated magnesium oxide powder excellent in thermal conductivity and moisture resistance, filling property when used as a filler for a resin, high in flowability of a resin composition after filling, and excellent in moldability as a result.SOLUTION: There is provided a coated magnesium oxide powder having a magnesium oxide powder exhibiting a particle internal cavity amount of 0.3 to 0.8 cm/g, a mode diameter of 0.2 to 1.0 μm and an inflection point diameter of 0.9 μm or more in a mercury penetration-type pore distribution, and a coated layer consisting of a magnesium phosphate compound on at least a part of the surface of the powder, and having the content of phosphorus in the coated magnesium oxide powder of 0.1 to 10 mass%.

Description

  The present invention relates to a coated magnesium oxide powder that can be used as a filler for a resin, and a method for producing the same. Moreover, this invention relates to the heat radiating member which consists of the resin composition containing the said covering magnesium oxide powder, and the said resin composition.

  The electronic device is composed of electronic components such as a laminate, a printed wiring board, and a multilayer wiring board. In electronic parts, resin compositions are usually used for prepregs, spacers, sealants, adhesive sheets, and the like, and various performances or characteristics are required for the resin compositions. For example, as a recent trend, mounting of large-capacity power elements in electronic devices and high-density mounting are seen, and accordingly, heat dissipation and moisture resistance superior to conventional ones are required for resin compositions and their applications. ing.

  Conventionally, silicon dioxide (hereinafter referred to as silica) and aluminum oxide (hereinafter referred to as alumina) have been used as a filler (filler) used in a resin composition for semiconductor encapsulation. However, the thermal conductivity of silica is low, and heat dissipation corresponding to an increase in the amount of heat generated due to high integration, high power, high speed, etc. is insufficient, causing problems in stable operation of the semiconductor. On the other hand, when alumina having higher thermal conductivity than silica is used, the heat dissipation is improved, but since alumina has a high hardness, there has been a problem that the wear of the kneader, the molding machine and the mold becomes severe.

  Therefore, magnesium oxide, which has a thermal conductivity that is an order of magnitude higher than that of silica and approximately twice that of alumina, has been studied as a material for resin fillers for semiconductor encapsulation. However, the magnesium oxide powder has higher hygroscopicity than the silica powder. Therefore, when magnesium oxide powder is used as a resin filler for semiconductor encapsulation, the absorbed water and magnesium oxide are hydrated and the volume of the filler expands, resulting in cracks, reduced thermal conductivity, etc. The problem was occurring. For this reason, providing moisture resistance to the magnesium oxide powder used as the resin filler for semiconductor encapsulation has been a major issue in ensuring long-term stable operation of the semiconductor.

  As a method for improving the moisture resistance of magnesium oxide powder, Patent Document 1 and Patent Document 2 include mixing an aluminum salt or a silicon compound and magnesium oxide powder, filtering off solids, drying, and firing. There is disclosed a method for producing a coated magnesium oxide powder, wherein the surface of the magnesium oxide powder is coated with a coating layer containing aluminum or a double oxide of silicon and magnesium.

JP 2003-34522 A JP 2003-34523 A

  However, although the coated magnesium oxide powder obtained by the above-described method has improved moisture resistance, the powder particles have an angular shape, so that the filling property to the resin is low, and the obtained resin composition There is a problem of low fluidity.

  The object of the present invention is to solve the above-mentioned problems, and is excellent in moisture resistance in addition to thermal conductivity. Further, when used as a filler for a resin, the fluidity of the resin composition after filling is high. An object of the present invention is to provide a coated magnesium oxide powder excellent in moldability and a method for producing the same. Another object of the present invention is to provide a resin composition containing the coated magnesium oxide powder and a heat dissipating member comprising the resin composition.

In the mercury intrusion pore distribution, the present invention has an interparticle void amount of 0.3 to 0.8 cm ³ / g, a mode diameter of 0.2 to 1.0 μm, and an inflection point diameter of 0.9 μm or more. The magnesium oxide powder shown and a coating layer made of a magnesium phosphate compound on at least a part of the surface of the magnesium oxide powder, and the phosphorus content in the coated magnesium oxide powder is 0.1 to 10 mass % Of the coated magnesium oxide powder.

  The present invention also relates to a filler comprising the coated magnesium oxide powder.

  Furthermore, this invention relates also to the resin composition containing resin and the said filler. The said resin composition can be used as heat radiating members, such as an adhesive agent or a semiconductor sealing agent.

Furthermore, the present invention includes B in an amount of 100 to 1000 ppm, Na in an amount of 300 ppm or less, K in an amount of 300 ppm or less, Cl in an amount of 0.02 to 0.5% by mass, and Si in terms of SiO _2. Magnesium oxide powder is obtained by calcining magnesium hydroxide having a purity of 98% or more and containing 0.1 to 0.8% by mass of Ca in terms of CaO in an amount of 0.5% by mass at 1000 ° C to 1200 ° C. Then, the magnesium oxide powder is mixed with a phosphorus compound and fired at 300 ° C. or higher to form a coating layer made of a magnesium phosphate compound on at least a part of the surface of the magnesium oxide powder. The invention also relates to a method for producing a coated magnesium oxide powder.

  According to the present invention, in addition to thermal conductivity, it is excellent in moisture resistance, and further, it has excellent filling properties when used as a filler for a resin, and the fluidity of the resin composition after filling is high. The coated magnesium oxide powder having excellent moldability can be provided.

Electron micrograph of the coated magnesium oxide powder produced in Example 1

  Hereinafter, the present invention will be specifically described.

  The coated magnesium oxide powder of the present invention has a magnesium oxide powder having specific physical properties and a coating layer formed on the surface and made of a magnesium phosphate compound. The coating layer made of a magnesium phosphate compound may be formed on the entire surface of the magnesium oxide powder, or may be formed only on a part of the surface of the magnesium oxide powder. The surface of the magnesium oxide powder that is not covered with the coating layer made of the magnesium phosphate compound may be exposed.

In the present invention, the magnesium oxide powder satisfies an inter-particle void amount of 0.3 to 0.8 cm ³ / g, a mode diameter of 0.2 to 1.0 μm, and an inflection point diameter of 0.9 μm or more. By forming a coating layer made of a magnesium phosphate compound on the surface of such magnesium oxide powder, the coated magnesium oxide powder of the present invention can be suitably used as a thermally conductive filler.

  In addition, each measured value is a numerical value measured in the mercury intrusion type pore distribution measuring device.

  The inflection point diameter and the amount of voids in the particle can be obtained from the cumulative pore volume curve. In the cumulative pore volume curve, the vertical axis represents the fine particle size obtained in order from the largest pore per unit weight of the sample. The cumulative pore volume, which is the cumulative value of the pore volume, is represented, and the horizontal axis represents the pore diameter.

  The inflection point is the point at which the cumulative pore volume curve rises rapidly. Depending on the measurement sample, the number of inflection points is not limited to one, and there may be a plurality of inflection points, but the inflection point with the largest pore diameter is defined as the inflection point of the present invention. The inflection point diameter is the pore diameter at the inflection point.

  If the inflection point diameter is less than 0.9 μm, the amount of fine particles increases, so that a sudden increase in viscosity occurs when filling the resin. Preferably, the inflection point diameter is 0.9 to 1.5 μm.

The amount of voids in the particles is the amount of voids smaller than the aggregated particle diameter present in the particles, and the amount of voids in the particles is the cumulative pores at pore diameters of 0.003 × 10 ^{−6 to} 100 × 10 ⁻⁶ m. The total pore volume represented by the volume is represented by a volume obtained by subtracting the cumulative pore volume at the inflection point.

When the void amount in the particle of the magnesium oxide powder is less than 0.3 cm ³ / g, the void in the particle is small, a sufficient amount of resin does not penetrate into the particle, and the mechanical strength of the resin composition deteriorates. . Moreover, thermal conductivity is also reduced. On the other hand, when the amount of voids in the particles exceeds 0.8 cm ³ / g, the voids in the particles exist deep inside the particles, so that the resin does not reach the inside of the voids sufficiently, and bubbles are generated between the particles and the resin to conduct heat. Sex is reduced. Preferably, the amount of voids in the particle is 0.3 to 0.7 cm ³ / g.

  The mode diameter can be obtained from mercury intrusion pore distribution measurement, and is the pore diameter corresponding to the maximum value of the log differential pore volume distribution curve. When the pore distribution of the magnesium oxide particles of the present invention is measured by a mercury intrusion measuring apparatus, the mode diameter corresponds to the diameter of the gap between the magnesium oxide particles. When the mode diameter of the magnesium oxide powder is less than 0.2 μm, the amount of fine particles increases, so that a sudden increase in viscosity occurs when filling the resin. On the other hand, when the mode diameter exceeds 1.0 μm, the amount of large particles increases, so that the mechanical strength of the resin composition deteriorates. Moreover, thermal conductivity is also reduced. Preferably, the mode diameter is 0.3 to 1.0 μm.

A coating layer made of a magnesium phosphate compound is formed on such magnesium oxide powder. With this coating layer, the moisture resistance of the magnesium oxide powder can be improved. The magnesium phosphate compound is, for example, a compound represented by a composition formula: Mg _x P _y O _z (x = 1 to 3, y = 2, z = 6 to 8).

  Since the coated magnesium oxide powder of the present invention has a coating layer made of a magnesium phosphate compound, it contains phosphorus as a constituent element. Content of phosphorus is 0.1-10 mass% with respect to the covering magnesium oxide powder of this invention. By including phosphorus in such a range, the coated magnesium oxide powder of the present invention can be excellent in moisture resistance. If the phosphorus content is less than 0.1% by mass, sufficient moisture resistance cannot be exhibited. Conversely, when the phosphorus content exceeds 10% by mass, the magnesium phosphate compound not only coats the surface of the magnesium oxide powder, but the magnesium phosphate compound alone forms particles or is coated. Since the layer is too thick, there is a disadvantage that the thermal conductivity is lowered.

  The coated magnesium oxide powder of the present invention is excellent in filling property when filling into a resin and has an advantage that the fluidity of the resin composition after filling is high. can do. As resin which can be used by this invention, a thermosetting resin or a thermoplastic resin is mentioned, for example. Although it does not specifically limit as a thermosetting resin, For example, a phenol resin, a urea resin, a melamine resin, an alkyd resin, a polyester resin, an epoxy resin, a diallyl phthalate resin, a polyurethane resin, or a silicone resin is mentioned. The thermoplastic resin is not particularly limited. For example, polyamide resin, polyacetal resin, polycarbonate resin, polybutylene terephthalate resin, polysulfone resin, polyamideimide resin, polyetherimide resin, polyarylate resin, polyphenylene sulfide resin, polyether ether Examples include ketone resins, fluororesins, and liquid crystal polymers.

  What is necessary is just to determine suitably the compounding quantity of the covering magnesium oxide powder in the resin composition of this invention according to the specification calculated | required by the resin composition, and it is not specifically limited. However, as an example, it may be used in the range of 0.1 to 100 parts by mass of the coated magnesium oxide powder with respect to 100 parts by mass of the resin.

  The resin composition containing the coated magnesium oxide powder of the present invention can be used in various fields depending on the properties of the resin. However, since the coated magnesium oxide powder of the present invention is excellent in thermal conductivity, it can be suitably used particularly in applications where heat dissipation is required. Moreover, the resin composition of this invention can be utilized as a semiconductor sealing material excellent in thermal conductivity and moisture resistance.

  Next, a method for producing the coated magnesium oxide powder of the present invention will be described.

  First, magnesium hydroxide which shows a predetermined physical property is obtained by baking magnesium hydroxide. The concentration of each impurity element contained in the magnesium hydroxide to be fired is adjusted in advance to a predetermined concentration, and the temperature at the time of firing is set to a range of 1000 to 1200 ° C., thereby obtaining magnesium oxide exhibiting predetermined physical properties. It becomes possible.

The different elements in magnesium hydroxide are as follows. B (boron): 100 to 1000 ppm (preferably 300 to 800 ppm), Na (sodium): 300 ppm or less (preferably 200 ppm or less), K (potassium): 300 ppm or less (preferably 200 ppm or less), Cl (chlorine): 0 0.02 to 0.5% by mass (preferably 0.15 to 0.3% by mass), Si (silicon): 0.02 to 0.5% by mass (0.05 to 0.15% by mass in terms of SiO ₂ ) ), Ca: 0.1 to 0.8 mass% (preferably 0.2 to 0.5 mass%) in terms of CaO. The concentration of these different elements can be adjusted by a conventional method. For example, when B is insufficient, it can be adjusted by adding boric acid or magnesium borate. When Cl is insufficient, it can be adjusted by adding hydrochloric acid or magnesium chloride. When Si is insufficient, it can be adjusted by adding sodium silicate, magnesium silicate, calcium silicate or the like. When calcium is insufficient, it can be adjusted by adding calcium hydroxide, calcium oxide, calcium carbonate or the like.

When B in magnesium hydroxide exceeds 1000 ppm, or Na or K exceeds 300 ppm, the obtained magnesium oxide does not satisfy the above-mentioned conditions for the void amount in the particle and / or the inflection point diameter. Moreover, when Ca in magnesium hydroxide is out of the range of 0.1 to 0.8% by mass in terms of CaO, or when Si is out of the range of 0.02 to 0.5% by mass in terms of SiO ₂ The obtained magnesium oxide does not satisfy the conditions of the mode diameter and / or the inflection point diameter described above, and the shape is not rounded. It is preferable to use magnesium hydroxide having a purity of 98% or more.

  Furthermore, it is preferable that the temperature at the time of baking magnesium hydroxide is the range of 1000-1200 degreeC. When the firing temperature is less than 1000 ° C., the obtained magnesium oxide does not satisfy the above-described conditions for the void amount in the particle, the mode diameter, and / or the inflection point diameter. Moreover, when a calcination temperature exceeds 1200 degreeC, the magnesium oxide obtained will not satisfy the conditions of the mode diameter and / or inflection point diameter mentioned above. The firing furnace and firing time are not particularly limited, and may be any firing furnace and firing time in which magnesium hydroxide can be converted to magnesium oxide at the temperature described above.

  The magnesium oxide obtained by firing magnesium hydroxide as described above is coarsely pulverized using a pulverizer as necessary. Thereby, a magnesium oxide powder is obtained. This magnesium oxide powder is mixed with a phosphorus compound and, if necessary, dried at a temperature of about 120 ° C. to 200 ° C., and then pulverized using a ball mill or the like to obtain a powder. By baking this powder at 300 ° C. or higher, a magnesium oxide powder in which a coating layer made of a magnesium phosphate compound is formed on at least a part of the surface can be obtained.

  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, and examples thereof include phosphoric acid, phosphate, and acidic phosphate. These may be used alone or in combination of two or more. Preferably it is acidic phosphate ester. Examples of the acidic phosphate ester 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.

  What is necessary is just to adjust the usage-amount of a phosphorus compound so that content of phosphorus with respect to the whole covering magnesium oxide powder which is a final product may be 0.1-10 mass%. For example, the phosphorus compound can be used in an amount of about 5 to 10% by mass with respect to the magnesium oxide powder.

  The temperature at the time of baking is 300 degreeC or more, Preferably it is about 300-700 degreeC. An example is firing at 500 ° C. for 1 hour. By this firing, the phosphorous compound is converted into a magnesium phosphate compound, whereby a coating layer made of the magnesium phosphate compound can be formed on the surface of the magnesium oxide powder.

  The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

(Measurement method of impurity element concentration)
About Ba and P, after melt | dissolving a sample in an acid, the density | concentration in a sample was computed by measuring mass using an ICP emission spectrometer (brand name: SPS-5100, Seiko Instruments make).

  About Cl, after melt | dissolving a sample in an acid, the density | concentration in a sample was computed by measuring mass using a spectrophotometer (brand name: UV-2550, Shimadzu Corporation make).

About Si and Ca, the density | concentration in a sample was measured using the fluorescent-X-ray apparatus (brand name: SPS-5100, Seiko Instruments make). However, respectively shown as the concentration of SiO ₂ in terms and terms of CaO.

  About Na and K, the density | concentration in a sample was measured using the atomic absorption photometer (brand name: Z-2300, Hitachi High-Technologies make).

(BET specific surface area measurement method)
The specific surface area was measured by a gas adsorption method using a specific surface area measurement apparatus (trade name: Macsorb 1210, manufactured by Mountec Co., Ltd.).

(Measurement of pore distribution)
Measurement of pore distribution (inflection point diameter, interstitial void volume, and mode diameter) Maximum inflection point diameter, interparticle void volume, and log differential pore volume distribution curve obtained by mercury intrusion pore distribution measurement The pore diameter (mode diameter) corresponding to the value was determined under the following conditions. The mercury intrusion pore distribution measuring device was measured using an Autopore 9410 manufactured by Micrometrics. As the mercury, a special grade mercury reagent having a purity of 99.5 mass% or more and a density of 13.5335 × 10 ³ kg / m ³ was used. The measurement cell used was a powder sample cell having an internal volume of 5 × 10 ⁻⁶ m ³ and a stem volume of 0.38 × 10 ⁻⁶ m ³ . The measurement sample was precisely weighed in a mass range of 0.10 × 10 ^{−3 to} 0.13 × 10 ⁻³ kg with a sample having a uniform particle size using a 330 mesh standard sieve (JIS-R8801-87) in advance. The measuring cell was filled. After mounting the measurement cell on the apparatus, the inside of the cell was kept under a reduced pressure at a pressure of 50 μHg (6.67 Pa) or less for 20 minutes. Next, mercury was filled in the measurement cell until the pressure became 1.5 psia (10342 Pa). Thereafter, mercury was injected in a pressure range of 2 psia (13790 Pa) to 60000 psia (413.7 MPa), and the pore distribution was measured.

The following formula (I) (Washburn's formula) was used to convert the intrusion pressure of mercury into the pore diameter.
D = − (1 / P) · 4γ · cosψ (I)
Where D: pore diameter (m),
P: mercury pressure (Pa)
γ: surface tension of mercury (485 dyne · cm ⁻¹ (0.485 Pa · m)),
Ψ: Mercury contact angle (130 ° = 2.26893 rad).

(Method of measuring moisture resistance)
A 10 g sample was weighed in a petri dish and set in a constant temperature and humidity machine (85 ° C./85 Rh%). After being kept in that state for one week, it was dried overnight in a 120 ° C. dryer. After drying, the weight was measured and the weight increase rate was calculated.

(Measurement method of thermal conductivity)
A sample of a high thermal conductivity resin composition having a diameter of 13 mm and a thickness of 2 mm obtained by completely curing the resin added with the product of the present invention is prepared. It was measured. The apparatus used was LFA-457 manufactured by NETZSCH. Specific gravity was measured by the specific heat and Archimedes method, and the thermal conductivity was calculated as the product of thermal diffusivity, specific heat and density.

(Measuring method of melt flow rate)
The resin composition was measured at a measurement temperature of 230 ° C. and a load of 2.16 kg according to JIS-K7210.

(Production method of resin composition)
The resin composition used in the measurement of the melt flow rate was prepared by the following procedure.
After melting 100 g of EEA (ethylene ethyl acrylate copolymer), 333 g of filler was added in small portions over about 10 minutes while observing the kneaded state, and finish kneading was further performed for 10 minutes. The roll interval at this time was 0.5 mm.

  After completion of the kneading, the compound was peeled off, and the recovered compound was cut to about 5 mm square and dried in a vacuum dryer at 90 ° C. for 1 hour to obtain a sample for measuring melt flow rate.

(Method for measuring composition of magnesium phosphate compound)
Using an X-ray diffractometer (trade name: RINT-Ultima III, manufactured by Rigaku), the composition of the magnesium phosphate compound coating layer was measured by an X-ray diffraction method using Cu-Kα rays.

Example 1
Adjusted so that CaO in the magnesium oxide produced by firing is 0.23 mass%, SiO ₂ is 0.07 mass%, Cl is 0.16 mass%, B is 402 ppm, Na is 11 ppm, and K is 9 ppm. The magnesium hydroxide having a purity of 99.2% was baked in an electric furnace at 1100 ° C. for 1 hour to prepare magnesium oxide.

  After pulverizing this magnesium oxide with a power mill, 5% by weight of isopropylpyrophosphate, which is an acidic phosphate, was added to magnesium oxide. Then, after drying at 120 ° C. for 2 hours, the mixture was pulverized with a ball mill and fired at 500 ° C. for 1 hour to obtain a target coated magnesium oxide powder.

  The obtained coated magnesium oxide powder was measured for the impurity element concentration, BET specific surface area, pore distribution, moisture resistance, thermal conductivity, and melt flow rate based on the above-mentioned method, and the results are shown in Table 1.

Moreover, when the composition of the coating layer on the surface of the obtained coated magnesium oxide powder was measured based on the method described above, it was found to be Mg ₂ P ₂ O ₇ .

  FIG. 1 is an electron micrograph of the obtained coated magnesium oxide powder. The particle shape of the coated magnesium oxide powder was spherical. Here, a spherical powder refers to a powder composed of rounded particles without corners, whereas an amorphous powder refers to a powder composed of angular particles in which a plurality of crystal particles are combined. Point to.

(Example 2)
A coated magnesium oxide powder was obtained under the same conditions as in Example 1 except that the firing temperature of magnesium hydroxide was changed to 1175 ° C. Each physical property was measured in the same manner as in Example 1, and the results are shown in Table 1.

(Example 3)
A coated magnesium oxide powder was obtained under the same conditions as in Example 1, except that the CaO of magnesium oxide was adjusted to 0.48% by mass. Each physical property was measured in the same manner as in Example 1, and the results are shown in Table 1.

(Example 4)
A coated magnesium oxide powder was obtained under the same conditions as in Example 1 except that the SiO of magnesium oxide was adjusted to 0.12% by mass. Each physical property was measured in the same manner as in Example 1, and the results are shown in Table 1.

(Example 5)
A coated magnesium oxide powder was obtained under the same conditions as in Example 1 except that the B concentration of magnesium hydroxide was adjusted to 700 ppm. Each physical property was measured in the same manner as in Example 1, and the results are shown in Table 1.

(Example 6)
A coated magnesium oxide powder was obtained under the same conditions as in Example 1 except that the Na concentration of magnesium hydroxide was adjusted to 200 ppm. Each physical property was measured in the same manner as in Example 1, and the results are shown in Table 1.

(Example 7)
A coated magnesium oxide powder was obtained under the same conditions as in Example 1 except that the K concentration of magnesium hydroxide was adjusted to 200 ppm. Each physical property was measured in the same manner as in Example 1, and the results are shown in Table 1.

(Example 8)
A coated magnesium oxide powder was obtained under the same conditions as in Example 1 except that the amount of acidic phosphate used was changed so that the phosphorus content in the coated magnesium oxide powder was 0.18% by mass. Each physical property was measured in the same manner as in Example 1, and the results are shown in Table 1.

Example 9
A coated magnesium oxide powder was obtained under the same conditions as in Example 1 except that the amount of acidic phosphate used was changed so that the phosphorus content in the coated magnesium oxide powder was 4.6% by mass. Each physical property was measured in the same manner as in Example 1, and the results are shown in Table 1.

(Comparative Example 1)
A coated magnesium oxide powder was obtained under the same conditions as in Example 1 except that the firing temperature of magnesium hydroxide was changed to 950 ° C. Each physical property was measured in the same manner as in Example 1, and the results are shown in Table 2.

(Comparative Example 2)
A coated magnesium oxide powder was obtained under the same conditions as in Example 1 except that the firing temperature of magnesium hydroxide was changed to 1400 ° C. Each physical property was measured in the same manner as in Example 1, and the results are shown in Table 2.

(Comparative Example 3)
A coated magnesium oxide powder was obtained under the same conditions as in Example 1 except that the CaO concentration of magnesium hydroxide was changed to 1% by mass. Each physical property was measured in the same manner as in Example 1, and the results are shown in Table 2.

(Comparative Example 4)
A coated magnesium oxide powder was obtained under the same conditions as in Example 1 except that the SiO concentration of magnesium hydroxide was changed to 4% by mass. Each physical property was measured in the same manner as in Example 1, and the results are shown in Table 2.

(Comparative Example 5)
A coated magnesium oxide powder was obtained under the same conditions as in Example 1 except that the B concentration of magnesium hydroxide was changed to 1200 ppm. Each physical property was measured in the same manner as in Example 1, and the results are shown in Table 2.

(Comparative Example 6)
A coated magnesium oxide powder was obtained under the same conditions as in Example 1 except that the Na concentration of magnesium hydroxide was changed to 400 ppm. Each physical property was measured in the same manner as in Example 1, and the results are shown in Table 2.

(Comparative Example 7)
A coated magnesium oxide powder was obtained under the same conditions as in Example 1 except that the K concentration of magnesium hydroxide was changed to 400 ppm. Each physical property was measured in the same manner as in Example 1, and the results are shown in Table 2.

(Comparative Example 8)
A coated magnesium oxide powder was obtained under the same conditions as in Example 1 except that the amount of acidic phosphate used was changed so that the phosphorus content relative to the entire coated magnesium oxide powder was 0.058% by mass. Each physical property was measured in the same manner as in Example 1, and the results are shown in Table 2.

(Comparative Example 9)
A coated magnesium oxide powder was obtained under the same conditions as in Example 1 except that the amount of acidic phosphate used was changed so that the phosphorus content relative to the entire coated magnesium oxide powder was 12.1% by mass. Each physical property was measured in the same manner as in Example 1, and the results are shown in Table 2.

Claims (13)

Magnesium oxide powder showing an in-particle void amount of 0.3 to 0.8 cm ³ / g, a mode diameter of 0.2 to 1.0 μm, and an inflection point diameter of 0.9 μm or more in a mercury intrusion pore distribution When,
A coating layer made of a magnesium phosphate compound on at least a part of the surface of the magnesium oxide powder;
The coated magnesium oxide powder, wherein the content of phosphorus in the coated magnesium oxide powder is 0.1 to 10% by mass. The magnesium phosphate compounds, composition _{formula: Mg x P y O z (} x = 1~3, y = 2, z = 6~8) represented by the coated magnesium oxide powder of claim 1, wherein.   A filler comprising the coated magnesium oxide powder according to claim 1.   A resin composition comprising a resin and the filler according to claim 3.   The resin composition according to claim 4, wherein the resin is a thermosetting resin.   The resin composition according to claim 5, wherein the thermosetting resin is a phenol resin, a urea resin, a melamine resin, an alkyd resin, a polyester resin, an epoxy resin, a diallyl phthalate resin, a polyurethane resin, or a silicone resin.   The resin composition according to claim 4, wherein the resin is a thermoplastic resin.   The thermoplastic resin is polyamide resin, polyacetal resin, polycarbonate resin, polybutylene terephthalate resin, polysulfone resin, polyamideimide resin, polyetherimide resin, polyarylate resin, polyphenylene sulfide resin, polyetheretherketone resin, fluorine resin, Or the resin composition of Claim 7 which is a liquid crystal polymer.   A heat dissipating member comprising the resin composition according to any one of claims 4 to 8. B and 100 to 1000 ppm, 300ppm or less Na, K and 300ppm or less, includes a Cl 0.02-0.5 wt%, and 0.02 to 0.5 wt% in terms of Si to SiO _2, Ca After obtaining magnesium oxide powder by calcining magnesium hydroxide having a purity of 98% or more containing 0.1 to 0.8 mass% in terms of CaO at 1000 ° C to 1200 ° C,
The magnesium oxide powder is mixed with a phosphorus compound and fired at 300 ° C. or higher to form a coating layer made of a magnesium phosphate compound on at least a part of the surface of the magnesium oxide powder. The manufacturing method of a coated magnesium oxide powder.   The manufacturing method of Claim 10 whose said phosphorus compound is 1 or more types of compounds selected from the group which consists of phosphoric acid, a phosphate, and acidic phosphate ester.   The phosphorus compound is selected from the group consisting of 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 The manufacturing method of Claim 11 which is 1 or more types of acidic phosphate ester.   The manufacturing method of any one of Claims 10-12 which uses the said phosphorus compound so that content of phosphorus in a covering magnesium oxide powder may be 0.1-10 mass%.