JP2022155316A - Particle material, production method thereof, and filler material - Google Patents

Abstract

To provide a particle material having high thermal conductivity and high electrical insulation.SOLUTION: A particle material may maintain a high insulation property by adhering closely to a metal material on the surface of the metal material and forming an insulating film comprising a metal oxide with a predetermined amount of pores having a predetermined pore diameter distribution. The particle material has a core composed of the metal material and the insulating film formed of the metal oxide having a thickness of 20 nm or more to cover the core without gaps. The particle material has a BET specific surface area of 0.1-10 m2/g. The particle material has a maximum pore volume peak between 1.7 nm and 100 nm in pore diameter in the analysis of pore distribution by BJH method. The volume of pores with pore diameters of 1.7-300 nm ranges from 0.3 mm3/g to 8.0 mm3/g. They have a volume-average particle size of 10 μm or more, a sphericity of 0.9 or more, and are dispersed to primary particles. Here, the pore diameter peak is calculated based on the pore volume calculated from the adsorption side of the BJH method.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a particulate material, a method for producing the same, and a filler material, and more particularly to a particulate material having excellent thermal conductivity, a method for producing the same, and a filler material.

Generating a large amount of heat has become a problem as the miniaturization of semiconductor devices progresses. The generated heat is required to be rapidly transferred from the semiconductor element to the outside. Therefore, a thermally conductive material (TIM) with high thermal conductivity is desired.

A conventional TIM is generally a resin composition in which a particulate material made of alumina or the like is dispersed in a resin material such as silicone resin (see, for example, Patent Document 1).

JP 2017-190267 A

By the way, it is expected that semiconductors will continue to be mounted at higher densities in the future, and an increase in heat generation is unavoidable. In addition, as the frequency of signals increases, even weak noise is affected, and there is a risk of malfunction of electronic components.

Here, particle materials made of metal materials with high thermal conductivity are known, but metal materials have high electrical conductivity and may cause short circuits when used in electronic devices as they are.

The present invention has been completed in view of the above-mentioned circumstances, and aims to provide a particle material using a metal material with high thermal conductivity and forming a film with high electrical insulation on the surface, a method for producing the same, and a filler material. Make it a problem to be solved.

The inventors of the present invention conducted extensive studies for the purpose of solving the above problems, and found that it is possible to maintain a high level of insulation by forming an insulating film made of a metal oxide on the surface of a metal material in close contact with the metal material. Found it. The insulating coating can maintain high insulation properties by providing a predetermined amount of pores with a predetermined pore diameter distribution.

That is, the particle material of the present invention that solves the above problems includes a core portion made of a metal material,
an insulating film formed of a metal oxide having a thickness of 20 nm or more and covering the core portion without gaps;
has
BET specific surface area is 0.1 to 10 m ² /g,
In the pore distribution analysis by the BJH method, the maximum value of the pore volume peak exists between 1.7 nm and 100 nm in pore diameter, and the pore volume with a pore diameter of 1.7 nm to 300 nm is 0.3 mm ³ /g to 8.0 mm ³ /g,
A volume average particle diameter of 10 μm or more,
sphericity is 0.9 or more,
Dispersed to primary particles.

Here, the pore diameter peak is calculated based on the pore volume calculated from the adsorption side of the BJH method.

Preferably, the metal material contains at least one of Al, Cu and Si in an amount of 50% by mass or more, and the insulating film is an oxide of the metal material. It is preferable that D10 is 25 μm or more and D90 is 65 μm or less. Also, D90/D10 is preferably 4.5 or less.

In the method for producing a particulate material of the present invention for solving the above problems, a molten material obtained by melting a metallic material containing 50% by mass or more of a metallic element is atomized in an inert atmosphere to form particles having a sphericity of 0.9. a granulation step for producing the above raw material granules;
In the pore distribution analysis by the BJH method, the maximum value of the pore volume peak exists between 1.7 nm and 100 nm in pore diameter, and the pore volume with a pore diameter of 1.7 nm to 300 nm is 0.3 mm ³ /g to 8.0 mm ³ /g until the pH is 1.3. an acid treatment step of immersing the raw material particulate material in an acid aqueous solution of ~2.4;
A dehydration step of dehydrating the acid aqueous solution to obtain a dehydrated product;
A washing step of washing the dehydrated product with an organic solvent to obtain a washed product;
a drying step of drying the washed material to obtain a dried material;
An oxide film forming step of heating the dried product in an oxidizing atmosphere at a temperature of 500° C. or higher and at a temperature at which the sphericity is not deformed to less than 0.9 to form an oxide film having a thickness of 20 nm or more on the surface;
have

By having a cleaning step with an organic solvent after the acid treatment step, an insulating film with high insulation can be formed.

Here, after the acid treatment step and before the washing step, it is preferable to include a dehydration step of dehydrating the acid aqueous solution to obtain a dehydrated product. Moreover, the atomizing method is preferably a step of supplying the molten material to the surface of a rotating metal disk.

Since the particle material of the present invention having the above structure has an insulating film formed on its surface, it can maintain high insulation even when placed in direct contact with a semiconductor circuit. In addition, even though an insulating film is formed, the sphericity is high, so the filling property is excellent and the contact between individual particles can be secured, so that high thermal conductivity can be exhibited. Since the particle material has a core portion made of metal, it can exhibit high thermal conductivity. This particulate material can be suitably employed as a filler material.

It is the result of the pore distribution analysis by the BJH method for the raw particulate material of Test 2. It is the result of the pore distribution analysis by the BJH method of the sample subjected to the acid treatment step once in Test 2. It is the result of the pore distribution analysis by the BJH method of the sample subjected to the acid treatment step six times in Test 2. 3 is an SEM photograph of Test 3; It is the result of measuring the amount of reflected electromagnetic waves, the amount of absorbed electromagnetic waves, and the sum thereof (the amount of electromagnetic wave shielding) for the resin composition of Sample 1 in Test 5. It is the result of measuring the amount of reflected electromagnetic waves, the amount of absorbed electromagnetic waves, and the sum thereof (the amount of electromagnetic wave shielding) for the resin composition of Sample 4 of Test 5.

The particulate material, method for producing the same, and filler material of the present invention will be described in detail below based on embodiments. Since the particle material of this embodiment has high thermal conductivity, it can be used as a TIM by dispersing it in a medium as some filler material (filler material of this embodiment). In particular, it is possible to provide a TIM with excellent insulating properties. The medium may be either liquid or solid, and examples thereof include oils, resin materials, and precursors of resin materials (such as monomers). Examples of resin materials and their precursors include epoxy resins and silicone resins. Since it is expected to exhibit the action of reflecting or absorbing electromagnetic waves, it can be expected to be applied to electromagnetic wave shielding materials, electromagnetic wave reflecting materials, and electromagnetic wave absorbing agents. In addition, since the dielectric constant can also be increased, it can be expected to be applied to fillers such as resin compositions for substrates, resin compositions for insulating materials, and resin compositions for antenna materials.

It can also be dispersed as a filler material in these media. When used as a filler material, the particle material of the present embodiment can be used alone, and a second particle material composed of other materials may be mixed. The second particle material is preferably composed of an insulating material such as ceramics such as alumina and silica.

(particle material)
The particulate material of this embodiment has a volume average particle diameter of 10 μm or more. The lower limit of the volume average particle diameter is preferably about 15 μm, 20 μm, and 25 μm, and the upper limit is preferably about 100 μm, 90 μm, 80 μm, 65 μm, 70 μm, and 75 μm. These lower and upper limits can be combined arbitrarily. Furthermore, a mixture of two or more different particle sizes may be used. By inserting particles with a small particle size into the gaps formed between particles with a large particle size, the filling rate as a whole is improved.

Further, when D10 is 15 μm or more and D90 is 95 μm or less, the particle size distribution of the particles constituting the particulate material becomes sharp. In particular, the lower limits of D10 may be 20 μm and 25 μm, and the upper limits of D90 may be 65 μm, 70 μm, 75 μm, 80 μm and 85 μm. These lower and upper limits can be combined arbitrarily. Furthermore, D90/D10 is preferably 4.5 or less, more preferably 3.5 or less.

The particulate material of this embodiment has a BET specific surface area of 0.1 to 10 m ² /g. The lower limit of the BET specific surface area can be exemplified by 0.1 m ² /g, 0.5 m ² /g and 1.0 m ² /g, and the upper limit is 1.0 m ² /g, 5.0 m ² /g, 10 m ² /g can be exemplified. These upper and lower limits can be combined arbitrarily. The BET specific surface area is measured using nitrogen gas.

The particle material of the present embodiment has a maximum pore volume peak in the pore diameter range of 1.7 nm to 100 nm in the pore distribution analysis by the BJH method. Examples of the lower limit of the pore diameter at which the pore volume peak is present are 1.7 nm, 5.0 nm and 20 nm, and the upper limits of the pore diameter are 10 nm, 20 nm and 100 nm. These upper and lower limits can be combined arbitrarily. The BET specific surface area is measured using nitrogen gas. Furthermore, the pore volume with a pore diameter of 1.7 nm to 300 nm is 0.3 mm ³ /g to 8.0 mm ³ /g, and the lower limits thereof are 0.3 mm ³ /g and 1.0 mm ³ /g. , 3.0 mm ³ /g, and the upper limit values are 1.0 mm ³ /g, 5.0 mm ^{3 /g, and 8.0 mm 3 /} g. These upper and lower limits can be combined arbitrarily. The measurement of pore diameter and pore volume by the BJH method is calculated from the amount of adsorption using nitrogen gas.

The particle material of the present embodiment has a sphericity of 0.9 or more, preferably 0.95 or more, more preferably 0.98 or more, and even more preferably 0.99 or more. The sphericity is calculated by taking a photograph with an SEM, and using the observed area and perimeter of the particle, (sphericity)={4π×(area)÷(perimeter) ² }. The closer to 1, the closer to a true sphere. Specifically, an average value obtained by measuring 100 particles using image analysis software (Asazo-kun, Asahi Kasei Engineering Co., Ltd.) is employed.

The particulate material of this embodiment has a core portion and an insulating coating. The core portion is made of a metal material. The metal material is not limited, but the total content of Al, Cu and Si is preferably 50% by mass or more. Also, the metal material may be a single metal composed solely of one element of Al, Cu, and Si, or an alloy composed of two or more of these elements. In addition to Al, Cu, and Si, other elements may be used as long as they have metallic properties as a whole.

Although the shape of the core portion is not particularly limited, it is preferably spherical. In particular, the sphericity is preferably 0.9 or more, more preferably 0.95 or more, 0.98 or more, or 0.99 or more. Although the particle size of the core portion is not particularly limited, it is preferably substantially the same as the particle size of the aforementioned particle material.

The insulating film is a film that covers the periphery of the core portion. The insulating coating is composed of metal oxide. The insulating film covers the surface of the core without gaps. The thickness of the insulating film is 20 nm or more. Moreover, it is preferable that the thickness is such that the insulating property can be maintained when a direct current of 10 V (preferably a direct current of 50 V) is applied to one particle. The thickness of the insulating coating is preferably 30 nm or more, more preferably 50 nm or more. The insulating film and the core portion are in close contact with each other. Whether or not there is close contact means that the gap between the insulating coating and the core portion is 5 nm or less when observing the cross section of the particle material.

The thickness of the insulating coating is measured by analyzing the constituent elements by XPS while scraping the surface of the particle material with an Ar laser at a rate of 10 nm/min. Specifically, the metal elements in the metal oxide forming the insulating coating and the metal elements forming the core portion were quantified, and the depth at which the quantities reversed was taken as the thickness of the insulating coating. The cutting speed with the Ar laser is calibrated with the material forming the insulating film.

For example, when an insulating film made of alumina is formed on the surface of a core portion made of aluminum, the peak intensity derived from Al in the metallic state and the peak intensity derived from Al of alumina in XPS measurement are used. was calculated, and the depth at which Al in the metallic state became relatively larger than Al in alumina (the depth cut by the Ar laser) was defined as the thickness of the insulating coating. In Al, the peak intensity of Al in the metallic state and the peak intensity of Al in the oxide state are considered to correspond to the relative amount of Al in each state, and the depth at which the peak intensities are reversed is the thickness of the oxide film. did.

The metal oxide can be an oxide of a metal element contained in the metal material constituting the core portion, and in that case, the composition ratio may be the same as or different from the composition ratio of the core portion. . Further, it may contain elements that are not contained in the core portion, or may not contain elements that are contained in the core portion.

Insulation retention is determined by measuring the current that flows when a predetermined voltage (10 V or 50 V) that requires direct insulation is applied to the particle material, and the current that flows is rounded to one decimal place. It was determined that the insulation was maintained when the current was 0 mA.

As an example of a specific measurement device, a set of tungsten needles with a tip diameter of 1.5 μm connected to a manipulator is sandwiched under a microscope with one of the particle materials, and a DC voltage current generator R6144 (ADC Co., Ltd.) The value of current flowing while gradually increasing the voltage from 0 V to a predetermined voltage was observed. As a result, it was determined that the insulating property was maintained when the flowing current was 0 mA.

In addition, a resin composition containing 50% or more of the particle material on a volume basis was prepared, and the volume resistivity was measured using a resistivity meter Hiresta-UP manufactured by Mitsubishi Chemical Analytic Co., Ltd., which was molded to a diameter of 20 mm and a height of 10 mm. did. Here, if the resistivity was 10 ¹¹ Ω·cm or more when a voltage of 1000 V was applied, it was determined that the film had insulating properties.

The voltage at which insulation can be maintained relatively increases as the insulating film becomes thicker. Also, the voltage at which insulation can be maintained varies depending on the material of the insulating film. Therefore, when the insulating property of the particle material is not sufficiently maintained, it can be realized by further increasing the thickness of the insulating film or by changing the material of the insulating film to a material with high insulating property.

The particulate material of the present embodiment can have a surface treatment layer formed by reacting a surface treatment agent such as a silane coupling agent, a silane compound, or an organosilazane. As the silane compound, an organic functional group such as an alkyl group, a phenyl group, an amino group, a phenylamino group, an epoxy group, an acrylic group, a methacrylic group, a vinyl group, an isocyanate group, or a styryl group is directly connected to the Si atom, or Compounds connected via spacers and having a SiH structure, hexamethyldisilazane, and the like are exemplified. The thickness of the surface treatment layer formed on the surface of the particle material is not particularly limited. Amounts of about 30%, 50%, 75%, 100%, 150%, and 200% can be exemplified.

(filler material)
The filler material of this embodiment comprises the particulate material of this embodiment. Filler materials can be used for TIMs, semiconductor encapsulants, underfill materials, and the like. The filler material can be in the form of a particulate material, a resin composition dispersed in a resin material, or a slurry composition dispersed in a solvent or the like. The filler material can contain other particles of the particulate material of the present embodiments. For example, particles of alumina or silica. The content of other particles can be about 10% to 90% based on the mass of the entire filler material. The content can be 20%, 30%, 40%, 50%, 60%, 70%, 80%, etc., and any range can be set with these contents as the lower limit or upper limit. can.

(Heat transfer material: TIM)
The TIM of this embodiment has the filler material of this embodiment and a resin material in which the filler material is dispersed as it is in the form of particles. Examples of the resin material include, but are not limited to, silicone and epoxy resin. These resin materials may be in a state before polymerization.

It is preferable to contain as much filler material as possible. For example, the upper limit of the content of the filler material can be about 70% or 80% based on the total volume.

(Method for producing particle material)
The method for producing the particulate material of the present embodiment is one of the methods by which the particulate material of the present embodiment described above can be produced. This manufacturing method is a method for manufacturing a particulate material from a metal material, and includes a granulating step, an acid treatment step, a washing step, a drying step, an oxide film forming step, and other necessary steps. A metal material is a material containing a metal element that constitutes the core portion. In particular, it is preferable that the total content of Al, Cu and Si is 50% by mass or more.

The granulating step is a step of granulating a molten metal material by an atomizing method in an inert atmosphere to produce raw material granules. Particles having a high degree of sphericity can be obtained from the raw material particles obtained by granulating in an inert atmosphere. In this specification, the inert atmosphere is, for example, an atmosphere composed of a gas containing an inert gas such as nitrogen gas or argon as a main component. The inert atmosphere is the process of solidifying the molten material to produce the raw material particles. After becoming a particulate material, it does not have to be in an inert atmosphere.

Although the atomization method is not particularly limited, it is a method of granulating a molten material by rapidly cooling it. In order to make a metal material into a molten material, a method of performing by any heating method, or a method of adopting a plasma atomizing method as an atomizing method and manufacturing a molten material as part of the atomizing method can also be adopted. Examples of the quenching method include a method of contacting the surface of a rotating metal disk, a method of spraying an inert gas such as nitrogen gas, and a method of spraying a liquid such as water. In particular, a method of contacting the surface of a rotating metal disk is desirable. The particle size distribution of the raw material particles can be controlled by changing the size, mass, material, rotation speed, etc. of the metal disk. For example, by increasing the number of rotations of the metal disk, the shear force applied to the molten material is increased, and the particle size of the resulting raw material particles can be reduced.

Since the sphericity of the raw particulate material obtained in the granulation step affects the sphericity of the particulate material produced as it is, the raw particulate material preferably has a high sphericity. For example, the sphericity of the raw material particles is preferably 0.9 or more, more preferably 0.95 or more, 0.98 or more, or 0.99 or more.

The acid treatment step contains acid and pH is 1.3. This is a step of immersing the raw material particles in an acid aqueous solution of ∼2.4 to obtain an acid-treated product. The acid aqueous solution is an aqueous solution containing an acid, and contains 50% or more (preferably 70% or more, 90% or more, 100%) of water based on the mass of the solvent, and water can be mixed with it. can contain any organic solvent. The acid is not particularly limited and includes hydrochloric acid, nitric acid, sulfuric acid, acetic acid, oxalic acid and the like. It is preferable to employ a pH in the range of 1.4 to 1.6.

In the acid treatment step, the immersion conditions such as the temperature of the acid aqueous solution and the immersion time are not particularly limited. exists, the acid-treated product has a pore diameter of 1.7 nm to 300 nm and a pore volume of 0.3 mm ³ /g to 8.0 mm ³ /g. The acid treatment step can also be performed multiple times by exchanging the aqueous acid solution. When the acid treatment step is carried out for a long period of time or is carried out multiple times, the formation of pores tends to progress, and the pore diameter tends to increase, and the pore volume tends to increase. In particular, 1.7 nm, 5.0 nm, and 20 nm can be exemplified as the lower limit of the pore diameter showing the maximum value of the pore volume peak, and 10 nm, 20 nm, and 100 nm can be exemplified as the upper limit. These upper and lower limits can be combined arbitrarily.

The pore volume with a pore diameter of 1.7 nm to 300 nm has a lower limit of 0.3 mm ³ /g, 1.0 mm ³ /g, and 3.0 mm ³ /g, and an upper limit of 1.0 mm ³ . /g, 5.0 mm ^{3 /g, and 8.0 mm 3 /} g can be exemplified. These upper and lower limits can be combined arbitrarily. It is preferable that D90/D10 of the pore diameter is 10 or less. Here, D10 is the pore diameter that reaches 10% based on the total volume when the pore volume is integrated from the smaller pore diameter, and D90 is the pore diameter that reaches 90%. The pore size distribution of the pore diameter and the pore volume are measured by the BJH method using the adsorption action of nitrogen gas.

The temperature of the acid aqueous solution in the acid treatment step is not particularly limited, but the lower limit values can be exemplified by 0°C, 10°C and 20°C, and the upper limit values can be exemplified by 50°C, 60°C and 70°C. These upper and lower limits can be combined arbitrarily. The treatment time for the acid treatment step is not particularly limited, but examples include lower limits of about 10 minutes, 30 minutes, and 60 minutes, and upper limits of about 60 minutes, 120 minutes, and 600 minutes. These upper and lower limits can be combined arbitrarily. The combination of aqueous acid temperature and treatment time achieves the proper pore diameter peak and pore volume as described above.

The washing step is a step of washing the acid-treated product with an organic solvent to obtain a washed product. Although the organic solvent is not particularly limited, one having miscibility with water is preferable. For example, ethanol, isopropyl alcohol, and ethyl methyl ketone can be used as the organic solvent, and it is particularly preferable to use isopropyl alcohol and ethyl methyl ketone. The washing step is preferably carried out to such an extent that the amount of the aqueous acid solution remaining in the organic solvent can be reduced to less than 2%.

It is preferable to have a dehydration step for dehydrating and removing the acid aqueous solution adhering to the acid-treated product before the washing step. The dehydration step is a step of separating the acid-treated product from the acid aqueous solution by filtration, centrifugation, natural sedimentation, or the like, and can also include a step of washing with pure water, in particular. When the step of washing with pure water is adopted, it is possible to have a step of removing adhering pure water by drying. Drying can be performed by heating or by reducing pressure.

The drying step is a step of drying the washed material to obtain a dried material. Although the drying method is not particularly limited, it is preferable to separate and remove the organic solvent by filtration, centrifugation, or the like, and then evaporate the organic solvent by heating or reduced pressure. It is preferable to carry out the drying process until the residual amount of the organic solvent is less than about 2%.

The oxide film forming step is a step of heating the dried product in an oxidizing atmosphere at a temperature of 500° C. or higher and at a temperature at which the sphericity is not deformed to less than 0.9. As a result, the oxide film is dehydrated, and the connection between the core portion and the oxide film is strong and no gap can be formed.

The oxidizing atmosphere can be in a gas containing oxygen such as oxygen gas or air, or in the coexistence of a substance that releases oxygen when heated.

As a heating temperature at which the sphericity is not deformed to less than 0.9, a temperature near the melting point of the metal material forming the core particles can be exemplified. Even if the dried material is heated to a temperature exceeding the melting point of the metal material, the dried material is not necessarily melted and deformed, and a temperature higher than the melting point may be employed. For example, when aluminum is used as the metal material, there are conditions under which the sphericity of the dried product does not decrease even if it is heated to a temperature of about 800° C., which is higher than the melting point of aluminum.

The lower limit of the heating temperature can be 550° C., 600° C., 650° C., or the like, and the upper limit can be a temperature about 100° C. to 140° C. higher than the melting point of the metal material. For example, when aluminum with a melting point of 660.degree. C. is used as the metal material, the upper limit of the heating temperature can be about 760.degree. C. to 800.degree.

The heating time is continued until an oxide film having a thickness of 20 nm or more is formed on the surface. For example, in the case of forming alumina as an oxide film from raw material particles made of aluminum, an oxide film having a desired thickness could be formed by heating in an air atmosphere for about 1 to 480 minutes. Appropriate heating time varies depending on the heating temperature. If the heating temperature is low, a relatively long heating time is preferable, and if the heating temperature is high, a relatively short heating time is preferable. The upper limit of the heating time includes 300 minutes, 240 minutes, 180 minutes, 120 minutes, 60 minutes, 30 minutes and 20 minutes, and the lower limit of the heating time is 3 minutes, 4 minutes, 5 minutes, 10 minutes and 15 minutes. minutes, 20 minutes, 30 minutes, and the like. The heating method is not particularly limited. For example, heating can be performed by a kiln such as a roller hearth kiln, a pusher kiln, or a rotary kiln.

An oxide film containing elements other than the elements constituting the raw material particles can be formed by attaching elements other than the elements constituting the raw material particles to the surface of the raw material particles before the oxide film forming step. For example, the raw particulate material can be immersed in a solution containing metal elements other than those constituting the raw particulate material and then dried, or the surface can be made to contain different types of elements by sputtering or vapor deposition.

After the oxide film forming step, a surface treatment layer can be formed on the surface. Surface treatment is performed by contacting the surface of the particulate material with a surface treatment agent. As a method of contacting the surface of the particle material, the surface treatment agent can be contacted as it is or after being dissolved in an appropriate solvent. When it is contacted as it is, it can be contacted in a liquid state or a gaseous state. The reaction can be promoted by heating at an appropriate temperature after or while contacting. Suitable temperatures include 80°C, 100°C, 150°C, 200°C, and 250°C.

(Test 1: Preparation of sample and evaluation of specific surface area)
A metal material made of metal aluminum was heated to 750° C. and melted, and the molten material was treated with a disc atomizer under an inert atmosphere (nitrogen atmosphere) to obtain raw material particles (particulation step). The obtained raw material particles had a sphericity of 0.99 and volume average particle diameters of 80 μm, 55 μm, 35 μm and 10 μm. The volume average particle size was controlled by controlling the number of rotations of the disk of the disk atomizer. Specifically, the volume-average particle diameter decreased as the number of rotations of the disk increased.

The obtained raw material particles were immersed in a 0.03N hydrochloric acid aqueous solution (pH 1.5) to obtain an acid-treated material (acid treatment step). The immersion conditions were 25° C. and 6 hours once. The acid-treated material was dehydrated by centrifugation to obtain a dehydrated material, and then washed with an organic solvent (isopropyl alcohol) to obtain a washed material, thereby eliminating residual acid. The washing was terminated when the amount of aqueous acid solution remaining in the organic solvent was less than 2%. Even without the dehydration step, a sample with no residual acid could be obtained by repeating the washing step. However, it was possible to reduce the amount of the organic solvent used in the washing process by performing the dehydration process.

The raw material particles and the washed material were heated at 600° C. for 180 minutes in an air atmosphere to form an oxide film to obtain the particle material of this example (oxide film forming step). The thickness of the oxide film was 80-100 nm. There was no change in the volume average particle size even after the oxide film forming process. In addition, D90/D10 was 1.6 to 3.0 and was 3.0 or less. Further, the sphericity was 0.99 and remained unchanged. Further, it was confirmed by SEM that even the primary particles were dispersed. Table 1 shows the measurement results of the specific surface area for each.

For all particle sizes, the specific surface area increased by acid treatment.

(Test 2: Evaluation of pore volume)
Next, raw material particles having a volume average particle diameter of 55 μm were evaluated. Particle materials were obtained by performing the oxide film forming process on the samples having the number of times of the acid treatment process set to 0, 1, and 6 times. For the specimens in which the acid treatment process was performed once and six times, the dehydration process and the washing process were performed before the oxide film formation process. The results of pore distribution analysis by the BJH method are shown in FIGS.

As is clear from FIGS. 1 to 3, the measurement results of the pore volume distribution and the pore surface area distribution of the raw material particle material before acid treatment (FIG. 1) and the acid-treated material after one acid treatment (FIG. 2) are shown. By comparison, in the raw material particles, the maximum peak of the pore volume was present at more than 100 nm, but after one acid treatment, the pore volume decreased within the range of 1.7 nm to 100 nm (3.5 nm). A maximum peak of The height of the maximum peak of the pore volume was slightly less than 10 times higher than before the acid treatment, and it can be assumed that new pores were formed after the acid treatment step.

Furthermore, when the acid treatment was repeated 6 times, although the maximum peak height of the pore volume and the pore diameter at the maximum peak did not change much (3.5 nm), the pore volume at a pore diameter larger than the maximum peak increased. It was found that the pore volume increased as a whole (Fig. 3). It is believed that this is because the pores formed by the acid treatment step have approximately the same pore diameter, and the formed pores fuse with adjacent pores to have a large pore diameter.

Regarding the pore volume with a pore diameter of 1.7 nm to 300 nm, changes before and after the acid treatment were examined. Table 2 shows the results.

As is clear from Table 2, the acid treatment increased the pore volume. It was found that increasing the number of acid treatments also increased the pore volume.

(Test 3: Examination of conditions for acid treatment process)
A raw material particulate material having a volume average particle diameter of 55 μm was subjected to an acid treatment step under conditions of pH 1.0, 1.4, and 2.5, and then subjected to an oxide film forming step, and the resulting particulate material was evaluated. rice field. Furthermore, the sample subjected to the acid treatment process under the condition of pH 2.5 was also evaluated in the case where the dehydration process was performed after the acid treatment process but the washing with an organic solvent (isopropyl alcohol) was not performed. The above conditions were used for the temperature and time for the acid treatment step. The obtained particle material was measured for pore volume with a pore diameter of 1.7 nm to 300 nm, and the results are shown in Table 3. A SEM photograph is shown in FIG.

As is clear from Table 3 and FIG. 4, the sample subjected to the acid treatment process at pH 1.0 was greatly deformed in particle shape. Moreover, the pore volume also showed a value greatly exceeding 8.0 mm ³ /g. In addition, the sample subjected to the acid treatment process at pH 2.5 did not have many pores on the surface, but because the washing process was not performed, precipitates were formed and the pore volume was 28.446 mm. ³ /g, which is very large.

On the other hand, the sample subjected to the acid treatment process at pH 1.4 had a pore volume of 0.320 mm ³ /g, and the surface was very smooth although formation of pores was observed.

(Test 4: Evaluation of thermal conductivity, volume resistivity and dielectric constant)
For raw material particles with a volume average particle diameter of 55 μm, a sample subjected to an acid treatment process under the conditions of pH 1.5 (sample 1) and pH 2.5 (sample 2), and a sample (sample 3) not subjected to an acid treatment process. was subjected to an oxide film forming step to form an oxide film and prepare a sample. The sample subjected to the acid treatment process was subjected to a dehydration process and a washing process before the oxide film forming process so that no acid remained.

Resin compositions were prepared and cured with the compositions shown in Table 4 for the samples subjected to the acid treatment process at pH 1.5 and 2.5, the sample not subjected to the acid treatment process, and the sample made of alumina (Sample 4). A resin composition for each sample was prepared. Thermal conductivity was measured for these resin compositions. The volume average particle size of the samples used was 45 μm for alumina and 55 μm for the other samples. The thermal conductivity was measured by a hot disk method using a disk having a diameter of 20 mm and a thickness of 8 mm prepared from the cured product of the resin composition.

In addition, a sample subjected to an acid treatment process at pH 1.5, a sample not subjected to an acid treatment process, and a cured product of a resin composition using alumina molded into a diameter of 20 mm and a height of 10 mm were evaluated by Mitsubishi Chemical Analytics. The volume resistivity was measured using a resistivity meter manufactured by Hiresta-UP. The results are shown in Table 4 together.

In addition, a sample subjected to an acid treatment process at pH 1.5 and a cured product of a resin composition using alumina molded into a diameter of 9 mm and a height of 30 mm were measured using an HP8362B apparatus manufactured by Agilent Technologies. , the dielectric constant was measured by the cavity resonance perturbation method at a measurement frequency of 1 GHz and a measurement temperature of 23°C. The results are shown in Table 4 together.

As can be seen from the table, Sample 1 (pH 1.5) has a higher thermal conductivity than Samples 2 (pH 2.5) and 4 (alumina) and is comparable to Sample 3 (no acid treatment step). there were. In addition, sample 1 (pH 1.5) showed a high volume resistivity comparable to sample 4 (alumina only), whereas sample 3 showed a very low volume resistivity. .

From the above results, it was found that the oxide film formed after the acid treatment process at pH 1.5 has the properties of both insulating properties comparable to those of alumina and thermal conductivity.

It was also found that the resin composition using Sample 1 had a higher dielectric constant than the resin composition using Sample 4. This is because the core part contains aluminum with high conductivity, so that the filler plays a role as a kind of conductor instead of a dielectric, and the insulating film formed on the particle surface makes the alumina This is considered to be due to the fact that an insulating property comparable to that of .

(Test 5: Evaluation of electromagnetic shielding performance)
40% by volume of Samples 1 and 4 prepared in Test 4 and 60% by volume of silicone resin (KR-220LP) were mixed and cured to obtain a resin composition. For the obtained resin composition, the amount of reflected electromagnetic waves, the amount of absorbed electromagnetic waves, and the sum thereof (the amount of electromagnetic wave shielding) were measured by the coaxial waveguide method, and the results are shown in FIGS.

As is clear from FIGS. 5 and 6, the resin composition using Sample 1 was found to be excellent in electromagnetic wave shielding performance, with a large amount of electromagnetic waves reflected and absorbed. On the other hand, the resin composition using Sample 4 composed of alumina exhibited only low electromagnetic wave shielding performance.

・Other tests As a result of conducting the same test as the above test using metallic copper and metallic silicon instead of metallic aluminum, a particle material dispersed to primary particles showing the same insulation as when metallic aluminum is used. was confirmed to be obtained.

Claims (10)

a core portion made of a metal material;
an insulating film formed of a metal oxide having a thickness of 20 nm or more and covering the core portion without gaps;
has
BET specific surface area is 0.1 to 10 m ² /g,
In the pore distribution analysis by the BJH method, the maximum value of the pore volume peak exists between 1.7 nm and 100 nm in pore diameter, and the pore volume with a pore diameter of 1.7 nm to 300 nm is 0.3 mm ³ /g to 8.0 mm ³ /g,
A volume average particle diameter of 10 μm or more,
sphericity is 0.9 or more,
Particulate material dispersed down to primary particles. The metal material has a total content of Al, Cu and Si of 50% by mass or more,
2. The particulate material according to claim 1, wherein said insulating coating is an oxide of said metal material. 3. The particulate material according to claim 1, wherein D10 is 25 [mu]m or more and D90 is 65 [mu]m or less. The particulate material according to any one of claims 1 to 3, wherein D90/D10 is 4.5 or less. a granulation step of producing raw material granules having a sphericity of 0.9 or more by granulating a molten material obtained by melting a metal material containing 50% by mass or more of a metal element by an atomizing method in an inert atmosphere;
In the pore distribution analysis by the BJH method, the maximum value of the pore volume peak exists between 1.7 nm and 100 nm in pore diameter, and the pore volume with a pore diameter of 1.7 nm to 300 nm is 0.3 mm ³ /g to 8.0 mm ³ /g until the pH is 1.3. an acid treatment step of immersing the raw material particulate material in an acid aqueous solution of 1 to 2.4 to obtain an acid-treated product;
A washing step of washing the acid-treated product with an organic solvent to obtain a washed product;
a drying step of drying the washed material to obtain a dried material;
an oxide film forming step of heating the dried product in an oxidizing atmosphere at a temperature of 500° C. or higher and at a temperature at which the sphericity is not deformed to less than 0.9 to form an insulating film made of a metal oxide having a thickness of 20 nm or more on the surface;
A method of making a particulate material having 6. The method for producing a particulate material according to claim 5, further comprising a dehydration step of dehydrating the acid aqueous solution to obtain a dehydrated product after the acid treatment step and before the washing step. 7. The method of producing particulate material according to claim 5, wherein the atomizing method is a step of supplying the molten material to the surface of a rotating metal disk. A filler material containing the particulate material according to any one of claims 1-4. a filler material according to claim 8;
a resin material that disperses the filler material in the form of particles;
A heat transfer material having 10. The heat transfer material of Claim 9, wherein the filler material further comprises a particulate material comprising alumina.

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