JP6639308B2 - Spherical AlN particles, spherical AlN filler, and method for producing spherical AlN particles - Google Patents

Description

  The present invention relates to a spherical AlN particle, a spherical AlN filler, and a method for producing a spherical AlN particle used as a semiconductor sealing material or the like.

  AlN (aluminum nitride) is a material having high thermal conductivity among ceramics, and a sintered body of AlN has been put to practical use as a substrate for a semiconductor. Since AlN is a material that is difficult to sinter, it is difficult to sinter alone with AlN, and Ca compounds and Y compounds are generally used as sintering aids. Since AlN is oxidized at a high temperature, it is general that the sintering is performed in an inert gas atmosphere containing no oxygen, for example, in a nitrogen gas atmosphere.

On the other hand, ceramic spherical particles are used for semiconductor sealing materials, insulating resin substrates, heat dissipation sheets, and the like. For these uses, spherical particles of an oxide such as SiO ₂ (silica) or Al ₂ O ₃ (alumina) are mixed with a resin, and these spherical particles are produced by a thermal spraying method. Things are widely used.

  In particular, spherical particles of alumina having higher thermal conductivity than silica are used for resin substrates, heat radiation sheets, heat radiation greases, and the like that require high thermal conductivity. However, the thermal conductivity of alumina is not necessarily high, about 30 W / mK for a sintered body, and the thermal conductivity of a material highly filled in a resin is only about several tens of W / mK.

In the future, when applied to components requiring more heat dissipation, such as power devices, it is necessary to further increase the thermal conductivity. In these applications, AlN is a promising material because insulation is required as well as high thermal conductivity.
However, since AlN is oxidized or decomposed at a high temperature, it is difficult to produce spherical particles by applying a thermal spraying method which is a general method for mass production of spherical particles.

In the thermal spraying method, a raw material powder is supplied into a high-temperature flame using a carrier gas or the like, and the raw material is melted to form a spheroidized molten raw material by surface tension. It is.
In the thermal spraying method, since a fuel gas and oxygen are required to form a flame, the raw material is melted in an oxidizing atmosphere.When spraying non-oxide, only spherical particles in which at least a part of the raw material is oxidized are used. I can't get it.

  Patent Literature 1 discloses a method for producing AlN spherical particles by thermal spraying by passing AlN powder through a flame in an oxidizing atmosphere in which combustible gas, carrier nitrogen, combustion oxygen, and dilution air burn. It has been disclosed.

As a method for obtaining spherical AlN particles, Patent Literature 2 discloses a method of nitriding spherical alumina particles.
In this technology, a mixture of carbon particles and dense Al ₂ O ₃ particles is irradiated with microwaves in a nitrogen atmosphere and heated to form a core composed of at least one of Al ₂ O ₃ and aluminum oxynitride. Thus, AlN particles having an AlN surface layer formed on the surface of the core can be produced.

  Further, as a method using a material other than dense alumina particles as a raw material, Patent Document 3 discloses a method of using a spherical granulated product of alumina powder or alumina hydrate powder as a starting material and performing reduction nitriding to obtain a spherical aluminum nitride powder. A method of making is disclosed.

JP 2011-190171 A JP 2012-41253 A International Publication No. 2011/93488

  As power devices are used in high-temperature environments or generate higher heat, higher heat conductivity is required for heat dissipating members. Spherical and dense AlN particles that can be filled and have high thermal conductivity are very useful.

Patent Literature 1 proposes a technique for spheroidizing an AlN raw material by thermal spraying.
However, in the method by thermal spraying, it is necessary to use a fuel gas and an oxygen gas or an oxygen-containing gas in order to form a flame, so that it is impossible to prevent the raw material AlN from being oxidized.

Further, in Patent Document 1, as shown in Examples, the remaining amount of AlN is 60% at the maximum, and 40% or more of AlN is oxidized and changed to Al ₂ O ₃ during the thermal spraying process.
For this reason, a structure that plays an important role in heat conduction is covered with Al ₂ O ₃ having a lower thermal conductivity than AlN. Therefore, when such particles are mixed with a resin, a high thermal conductivity cannot be obtained.

Patent Literature 2 proposes a method of nitriding using dense Al ₂ O ₃ spherical particles as a raw material.
However, when dense Al ₂ O ₃ particles are used as a raw material, the nitridation reaction occurs from the surface, so that AlN is formed on the surface layer, but the inside has low thermal conductivity, such as Al ₂ O ₃ and AlON (aluminum oxynitride). ).

When only the surface layer is converted to AlN in this way, the thermal conductivity when mixed with the resin becomes lower than that of particles in which the inside is AlN. Further, when the dense Al ₂ O ₃ particles are nitrided, voids are generated between the nitrided AlN layer and the inner core (Al ₂ O ₃ ) during the nitriding reaction. When mixed with the resin, the AlN layer is peeled off. Alternatively, the heat conduction is reduced by the gap.

Patent Literature 3 discloses a technique for reducing and nitriding spherical granules of alumina powder or alumina hydrate powder.
However, when this method is used, spherical AlN particles can be obtained, but it is preferable to use a material having a specific surface area of 30 to 500 m ² / g as a raw material of the spherical AlN particles.

  This is because if the specific surface area of the granulated material is too small, the voids between the particles are closed in the temperature raising process or the heat treatment process in the reductive nitriding process, and the reductive nitriding to the inside of the spherical granulated product is sufficiently performed. This is because there is a problem that the user is no longer able to do so.

  However, when a material having a large specific surface area, that is, a material having a small particle size, is used as the raw material of the granulated powder, the packing density of the raw material powder in the granulated powder becomes low, and many voids are formed even in the reductive nitriding process at a high temperature. Since the reaction with AlN occurs while remaining, there is a problem that many voids remain on the surface or inside of the finally obtained spherical AlN particles.

  For example, although the specific surface area of the spherical AlN powder of Patent Document 3 is generally high, this indicates that many fine pores remain, and therefore, the spherical AlN powder of Patent Document 3 is sufficiently high. Thermal conductivity may not be obtained.

Patent Document 3 also states that the spherical granulated product can be supplied to the reduction nitriding process after the heat treatment process. At this time, the heat treated product has a specific surface area of a certain level or more (for example, 2 m ² / g or more). It should have. Specifically, a spherical granulated product of γ-alumina obtained by heat-treating a spherical granulated product of aluminum hydroxide or boehmite at a temperature of about 600 ° C. for a certain period of time or a constant temperature of 1100 ° C. or higher It is stated that spherical granules of α-alumina obtained by heat-treating for a long time can be supplied to a reduction nitriding step.
However, when heat treatment is performed as a pretreatment of the reduction nitridation step, the heat treatment is performed twice, and thus there is a disadvantage that the manufacturing cost is increased.

  As described above, it was difficult to obtain dense AlN particles having high thermal conductivity with the conventional technology.

  In view of the above problems of the prior art, the present invention can be used as filler particles oriented to high filling properties and high thermal conductivity, is denser than the conventional one, and has a high thermal conductivity. It is an object of the present invention to provide spherical AlN particles having a high content and a method for producing the same.

As a result of intensive studies to solve the above problems, the inventor has found that an Al ₂ O ₃ powder having a predetermined particle size range contains a compound of at least one of La, Dy, and Er and a compound of Si. Are mixed at a predetermined ratio, and the granulated material granulated into a sphere is mixed with carbon powder and nitrided at a high temperature. It has been found that spherical AlN particles which can also be applied can be produced.

  Further, the manufactured spherical AlN particles contain a predetermined ratio of at least one compound of La, Dy, and Er and a compound of Si, and the content ratio of AlN is 80 wt% or more. It has a relative density of 90% or more of the density and can have a circularity of 0.85 to 1.00, and it has been found that this feature has higher filling property and higher thermal conductivity than the conventional one.

The gist of the present invention is as follows.
[1] Spherical particles containing at least one compound of La, Dy, and Er, a compound of Si, and AlN,
0 relative to the weight 100 wt% of the whole grain, said La, Dy, any one or more compounds of Er total 0.01-0.5% in terms of oxide, a compound of the Si in terms of SiO _2. 0.01 to 0.5 wt%, the AlN is contained in a proportion of 80 wt% or more,
Has a relative density of 90% or more of the theoretical density,
Spherical AlN particles having a circularity of 0.85 to 1.00.

[2] A spherical AlN filler comprising a plurality of the spherical AlN particles according to the above [1],
A spherical AlN filler having an average particle diameter (D50) of 5 to 150 μm.

[3] The method for producing spherical AlN particles according to the above [1],
A raw material powder mixing step of mixing an Al ₂ O ₃ powder having an average particle size of 0.05 to 4 μm with a powder of at least one compound of La, Dy, and Er and a powder of a compound of Si;
A granulation step of granulating the mixture produced in the raw material powder mixing step into a sphere,
A carbon powder mixing step of mixing the spherical granules produced in the granulation step with carbon powder,
A nitriding step of heat-treating and nitriding the mixture generated in the carbon powder mixing step at a temperature of 1400 to 1800 ° C. in a nitrogen atmosphere.
In the raw material powder mixing step, the ratio of the compound after mixing is 0.008 wt.% In terms of oxides by dividing the powder of at least one of La, Dy, and Er into 100 wt% of Al ₂ O ₃ powder. ～0.565Wt%, and, 0.008～0.565Wt% said compound of Si in terms of SiO _2, characterized by mixing to contain, method for producing spherical AlN particles.

[4] The method for producing spherical AlN particles according to [3], wherein in the granulating step, granulation is performed by a spray drying method.

[5] The method for producing spherical AlN particles according to [3] or [4], wherein the heat treatment is performed by microwave in the nitriding step.

[6] The method for producing spherical AlN particles according to any one of [3] to [5], wherein the temperature of the heat treatment in the nitriding step is 1600 to 1800 ° C.

  ADVANTAGE OF THE INVENTION According to this invention, the spherical AlN particle which can be used as filler particle | grains which aimed at high filling property and high thermal conductivity, is denser than before, and has high AlN content for high thermal conductivity, and its manufacturing method are provided. Is done.

FIG. 3 is an EPMA element mapping diagram of a cross section of a spherical AlN particle according to one example. FIG. 4 is an EPMA element mapping diagram of a cross section of a spherical AlN particle according to one comparative example.

The spherical AlN particles of the present invention are obtained by adding a compound of at least one of La, Dy, and Er to a total of 0.01 to 0.5 wt% in terms of oxide and a compound of Si with respect to 100 wt% of the total weight of the particles. 0.01-0.5% in terms of SiO _2, AlN and 80 wt% or more, in a proportion of, 90% or more of the relative density of the theoretical density, have a circularity of 0.85 to 1.00 .

The spherical AlN particles according to the present invention are 0.008 to 0.565 wt% of at least one compound of any one of La, Dy, and Er and 0.008 to 0.565 wt% in 100% by weight of Al ₂ O ₃ powder. % Of a Si compound, and spherical and granulated and dried granulated powder is mixed with carbon powder and heat-treated at a high temperature.

First, raw materials used in the method for producing spherical AlN particles of the present invention will be described.
(Al ₂ O ₃ powder)
Al ₂ O ₃ powder used as a raw material of Al ₂ O ₃ is an average particle size (D50) of it is desirable to use those 0.05～4Myuemu. When an Al ₂ O ₃ powder having an average particle size (D50) smaller than 0.05 μm is used, filling of the granulated powder obtained by granulation and drying with Al ₂ O ₃ powder in a granulation step described below. Since the ratio tends to be low, voids are likely to remain in the finally obtained spherical AlN particles, and particles having high thermal conductivity cannot be obtained. When Al ₂ O ₃ powder having an average particle diameter (D50) of more than 4 μm is used, the inside is hardly nitrided to form AlN, and particles having high thermal conductivity cannot be obtained. Further, it is desirable to use Al ₂ O ₃ powder having a specific surface area of 30 m ² / g or less even in the above average particle size range. When the specific surface area is larger than 30 m ² / g, voids remain in the obtained spherical AlN particles, and high thermal conductivity cannot be obtained.
The compounds of La, Dy, Er and the Si compound act as sintering aids that promote sintering before the Al ₂ O ₃ powder used as the raw material is nitrided or sintering of the AlN particles after the nitriding. It is effective to obtain dense spherical particles.

Here, the granulated powder is not excessively dense and includes voids, so that the nitriding reaction occurs not only on the surface of the spherical particles but also inside the granulated powder, so that the AlN content is 80%. The above spherical AlN particles can be obtained. When attempting to obtain spherical AlN particles having a high AlN content by using dense Al ₂ O ₃ spherical particles, AlN on the surface grows, the surface irregularities increase, and the circularity decreases. In the AlN particles of the present invention, since the individual Al ₂ O ₃ particles contained in the granulated powder are nitrided to form AlN, even if the AlN content becomes 80% or more, the surface unevenness does not increase. Spherical AlN particles having a high circularity of 0.85 to 1.00 can be obtained.

In addition, by using fine Al ₂ O ₃ powder as a raw material, sintering of Al ₂ O ₃ before nitriding occurs, but sintering of AlN particles is easy to progress because AlN particles after nitriding are also fine, Dense spherical AlN particles having a relative density of 90% or more of the theoretical density can be obtained.

Due to these effects, 0.01 to 0.5 wt% of La, Dy, or Er in terms of oxide and 0.01 to 0.5 wt% of Si in terms of SiO ₂ are contained. A spherical AlN having a content ratio of 80% by weight or more, a relative density of 90% or more of the theoretical density calculated from the AlN content ratio, and a circularity of 0.85 to 1.00. Particles can be obtained.

The spherical AlN particles of the present invention contain 0.01 to 0.5 wt% of Si in terms of SiO ₂ together with at least one of La, Dy and Er in terms of oxide. When Si is present together with at least one of La, Dy, and Er, an effect of promoting sintering of Al ₂ O ₃ before nitriding can be obtained.

By sintering Al ₂ O ₃ before nitriding, the Al ₂ O ₃ particles are combined by neck formation, and a strong skeleton of Al ₂ O ₃ is formed while maintaining the spherical shape of the granulated powder. Also, when AlN is generated by nitriding, the reaction proceeds while maintaining the spherical shape, and spherical AlN particles having high circularity can be obtained.

However, if the sintering of Al ₂ O ₃ proceeds excessively before nitriding proceeds, the voids in the granulated powder will be closed, and the nitrogen required for the reaction inside the granulated powder will not be supplied. It becomes impossible to obtain spherical AlN particles having a high AlN content.

For this reason, 0.008 to 0.565 wt% in terms of oxide, which is the optimum addition amount for causing sintering of appropriate Al ₂ O ₃ , is calculated as SiO ₂ together with at least one of La, Dy, and Er. It is important to add 0.008 to 0.565 wt% of Si to Al ₂ O ₃ at a high temperature. In addition, at least one compound of La, Dy, and Er and the Si compound are converted to oxides at high temperatures. Is desirable. The simultaneous presence of the oxides of La, Dy, and Er and SiO ₂ has the effect of increasing the AlN content of the spherical AlN particles. This is because La ₂ O ₃ , Dy ₂ O ₃ , Er ₂ O ₃ and SiO ₂ , Al ₂ O ₃ dissolve nitrogen into the liquid phase formed at a low temperature, and a reaction occurs in which AlN precipitates, thereby causing the formation of AlN. It is thought to promote.

  In order to obtain such an effect, it is necessary to add not only the compound of at least one of La, Dy, and Er and the compound of Si but also the two simultaneously.

The eutectic temperature of the La, Dy, and Er oxides and Al ₂ O ₃ is as high as about 1800 ° C., and the eutectic point of the Al ₂ O ₃ , even when two or more kinds of La, Dy, and Er oxides are used. Remains hot. Therefore, even if one or more of La, Dy, and Er oxides and Al ₂ O ₃ are added, in a temperature range of 1300 to 1600 ° C. where Al ₂ O ₃ sinters, Al ₂ O ₃ hardly contribute to sintering, thus occurred nitriding of Al ₂ O ₃ before the sintering of Al ₂ O ₃ is proceeds.

However, La, Dy, if oxide and SiO ₂ and Al ₂ O ₃ of Er coexist, since eutectic point serving as a low temperature of 1400 ° C. or less, the effect of sintering promoting the Al ₂ O ₃ by liquid phase product Obtainable.

By adding a rare earth oxide other than La, Dy, and Er simultaneously with SiO ₂ , the effect of promoting sintering of Al ₂ O ₃ can be obtained. However, as a result of extensive studies by the inventors, when a rare earth oxide other than La, Dy, and Er is used, sintering of Al ₂ O ₃ tends to proceed earlier as compared to La, Dy, and Er. As a result, the granulated powder becomes too dense before nitriding proceeds, and it has become clear that it is difficult to obtain particles having a high AlN content. When a compound of La, Dy, and Er is used, a nitriding reaction occurs while sintering of Al ₂ O ₃ proceeds appropriately, so that it is possible to obtain a dense spherical AlN particle having a high AlN content according to the present invention. It becomes possible.

The present inventor has further studied optimization of the added amounts of La, Dy, Er and Si, in view of the above findings. As a result, at least one of La, Dy, and Er is 0.008 to 0.565 wt% in terms of oxide and Si is 0.008 to 0 in terms of SiO _{2 in} terms of Al ₂ O ₃ 100 wt%. By adding .565 wt%, it was found that sintering of Al ₂ O ₃ before reduction nitridation proceeds moderately in the process of raising the temperature of reduction nitridation or in the process of maintaining the temperature at a high temperature for reduction nitridation. Invented the invention. This effect is obtained by forming a liquid phase at a high temperature when any of La, Dy, and Er and Si coexist in an oxide state. Al ₂ O ₃ are bonded to each other to the extent that they do not impede the penetration into the powder, and during the subsequent nitriding, the powder is densified while maintaining the shape of the granulated powder, so that more dense spherical AlN particles can be obtained. Become.

  If the amount of the Si compound is less than 0.008 wt% in terms of oxide, the effect of promoting sintering of AlN cannot be obtained. Dense spherical AlN particles cannot be obtained.

  When the content of any one of La, Dy, and Er is more than 0.565 wt% in terms of oxide, sintering of AlN progresses rapidly, shrinkage becomes uneven, and the shape of the particles becomes irregular. Therefore, spherical particles having a sufficiently high circularity cannot be obtained.

In terms of the effect of accelerating the sintering of AlN, it is desirable to use one or more of the compounds of La, Dy, and Er and the Si compound that becomes an oxide at a high temperature.
The sintering of AlN proceeds by liquid phase sintering using a liquid phase generated by at least one of La ₂ O ₃ , Dy ₂ O ₃ , and Er ₂ O ₃ and SiO ₂ and Al ₂ O _3. The generation of a liquid phase containing at least one of La ₂ O ₃ , Dy ₂ O ₃ and Er ₂ O ₃ has an effect of promoting sintering of AlN.

When the amount of Si in terms of SiO ₂ is less than 0.008 wt%, sintering of Al ₂ O ₃ before nitriding does not proceed, a skeleton is not formed before nitriding, and the sintering occurs during nitriding or sintering of AlN. It is difficult to obtain particles having a high degree of circularity.

When Si is contained in excess of 0.565 wt%, sintering of Al ₂ O ₃ before nitriding proceeds excessively, pores on the surface of the granulated powder are closed, and nitriding inside the granulated powder does not progress, and AlN Particles having a low ratio of, it is not possible to obtain particles having a high thermal conductivity.

Furthermore, if the sintering of Al ₂ O ₃ does not occur uniformly, the granulated powder will shrink in an irregular shape, and AlN particles with a high circularity cannot be obtained.
In order to make the sintering of Al ₂ O ₃ uniform, SiO ₂ and any one of La ₂ O ₃ , Dy ₂ O ₃ and Er ₂ O ₃ are used so that rapid sintering does not occur locally. It is important to add the above in an appropriate amount, that is, in the range of 0.008 to 0.565 wt%, and to uniformly disperse and mix these added components with the Al ₂ O ₃ powder.

Further, SiO ₂ contained as an impurity in the Al ₂ O ₃ powder used as a raw material often exists in a state of being confined inside, for example, in a form of solid solution in Al ₂ O _3, and the progress of sintering May be less effective. Further, since the amount of SiO ₂ contained as impurities in the high-purity raw material Al ₂ O ₃ powder is extremely small, the amount of Si in AlN particles in terms of SiO ₂ alone does not become 0.01 wt%. Therefore, in addition to SiO ₂ contained in the raw material Al ₂ O ₃ powder, it is necessary to add a Si compound within an appropriate range defined in the present invention.

Si compound is present in the grain boundaries during sintering of Al ₂ O _3, the effect is obtained which promotes sintering by generating a liquid phase at the grain boundary, Al preferably in the form of SiO ₂ or the like powder _A high effect can be obtained by adding it to the ₂ O ₃ powder raw material. Further, it is possible to obtain the same effect by generating a SiO ₂ during sintering of Al ₂ O ₃ in Si compounds other than SiO _2.

  The contents of La, Dy, Er and Si contained in the AlN spherical particles can be measured by an atomic absorption method.

When the content ratio of AlN in the spherical AlN particles is 80% or more, high thermal conductivity can be obtained when mixed with a resin or the like.
When the content ratio of AlN is less than 80%, a large amount of components having low thermal conductivity such as unreacted Al ₂ O ₃ and AlON which is a reaction intermediate product is included, so that the thermal conductivity when mixed with the resin. Therefore, the content ratio of AlN in the spherical AlN particles is preferably 80% or more.

The AlN content ratio of the spherical AlN particles is measured by analysis such as X-ray diffraction. When measuring by X-ray diffraction, the content ratio of AlN can be calculated by calculating the intensity ratio of the strongest peaks of AlN, Al ₂ O ₃ , and AlON.

  By setting the density of the spherical AlN particles to a relative density of 90% or more of the theoretical density, particles having a high thermal conductivity can be obtained.

The term theoretical density, using the theoretical density of AlN and Al ₂ O _3, AlON, AlN was measured by an analysis such as X-ray diffraction, the theoretical density calculated from the content of Al ₂ O _3, AlON.

The spherical AlN particles of the present invention contain a compound composed of Si and at least one of La, Dy, and Er in addition to the above-described Al compound. However, the existence form of the compound of at least one of La, Dy, and Er and the Si compound may not be known in some cases. In this case, since it is difficult to calculate the theoretical density in consideration of the compounds of La, Dy, Er and Si, here, the compounds of La, Dy, Er and the Si compound which are smaller in content than the Al compound are used. Without consideration, the theoretical density is calculated assuming that the particles are composed of AlN, Al ₂ O ₃ and AlON.

  When the relative density of the spherical AlN particles is 90% or less, the particles have voids of 10% or more inside, and the thermal conductivity of the spherical AlN particles decreases.

  When the spherical AlN particles do not substantially contain voids, the relative density is 100%. As described above, the theoretical density is calculated without considering the La, Dy, Er and Si compounds, and the relative density is calculated. To calculate the density, the theoretical theoretical density can exceed 100%.

  The density of the spherical AlN particles can be measured by any one of a pycnometer method, a suspension method, and a gas displacement method based on JIS-R1620 “Method of measuring particle density of fine ceramic powder”.

By setting the circularity of the spherical AlN particles in the range of 0.85 to 1.00, high fluidity is obtained, and the spherical AlN particles can be used as a filler having good filling properties.
In addition, the filler referred to in the present invention refers to an aggregate composed of a plurality of particles as a filler.

  If the degree of circularity is lower than 0.85, a large amount of irregularly shaped particles are contained, and it is difficult to increase the filling rate when mixed with a resin, which is not desirable.

  The circularity can be measured by a commercially available flow type particle image analyzer. Further, it can be obtained from a micrograph of a scanning electron microscope (SEM) or the like using image analysis processing software as follows. A photograph of the sample of the AlN particles is taken, and the area and the peripheral length of the AlN particles (two-dimensional projection) are measured. Assuming that the AlN particle is a perfect circle, calculate the circumference of the perfect circle having the measured area. The degree of circularity is determined from the equation of degree of circularity = circumference / perimeter. When the circularity is 1, a perfect circle is obtained. That is, the closer the circularity is to 1, the closer to a perfect circle.

When manufacturing spherical AlN particles, a large number of particle groups are manufactured in one lot, and it is desirable that the average particle diameter (D50) of these spherical AlN particle groups is 5 to 150 μm. If the average particle size exceeds 150 μm, it may be difficult for nitrogen necessary for nitriding Al ₂ O ₃ to enter the inside of the particle, and the particle may have Al ₂ O ₃ or the like remaining at the center of the particle. There is. In the case of particles smaller than 5 μm, Al ₂ O ₃ may be sintered and agglomerated with other particles during the process of nitriding to AlN, which may reduce the circularity. These spherical AlN particles can be used as a spherical AlN filler. Therefore, it is preferable that the spherical AlN filler composed of the spherical AlN particles also has an average particle diameter (D50) of 5 to 150 μm.

  Here, the average particle size can be determined by, for example, particle size distribution measurement by a laser diffraction method.

  In addition, the average particle size here is called a median diameter, and the particle size distribution is measured by a method such as a laser diffraction method, and the particle size at which the cumulative frequency of the particle sizes becomes 50% is determined as the average particle size ( D50).

As described above, the spherical AlN particles according to the present invention have a weight ratio of 0.008 to 0.565 wt% of one or more compounds of La, Dy, and Er and 100 wt% of Al ₂ O ₃ powder. A powder obtained by mixing 008 to 0.565% by weight of an Si compound and then granulating into a spherical shape is mixed with a carbon powder and nitrided at a high temperature. Hereinafter, the production of the spherical AlN particles of the present invention will be described in the order of steps.

<About granulation>
A slurry is prepared by mixing a raw material powder of Al ₂ O ₃ powder, at least one compound of La, Dy, and Er and a compound of Si with a solvent such as water and an additive such as a dispersant. At this time, it is desirable to add a binder in order to obtain a spherical granulated powder that is hard to break. This slurry is granulated into a sphere using a method such as spray drying. Spherical AlN particles obtained by nitriding the granulated powder have almost the same particle size as the granulated particles. Therefore, by adjusting the slurry concentration and the granulation conditions so that the average particle diameter (D50) of the granulated powder is 5 to 150 μm, it is possible to obtain the desired spherical AlN particles.

(Al ₂ O ₃ powder)
As the raw material powder to be used, it is desirable to use an Al ₂ O ₃ powder having an average particle size (D50) of 0.05 to 4 μm. When an Al ₂ O ₃ powder having an average particle diameter (D50) smaller than 0.05 μm is used, the filling rate of the Al ₂ O ₃ powder in the granulated powder obtained by granulation and drying tends to be low. Voids are likely to remain in the resulting spherical AlN particles. When Al ₂ O ₃ powder having an average particle diameter (D50) of more than 4 μm is used, the strength of the granulated powder is reduced, the spherical granulated powder is broken, and the circularity of the obtained AlN particles is reduced. When the Al ₂ O ₃ powder is nitrided into AlN, the surface unevenness increases and the circularity decreases, so it is difficult to increase the filling rate when mixing with the resin. May be.

The average particle diameter of the Al ₂ O ₃ powder is measured by a median diameter (D50) by, for example, particle size distribution measurement by a laser diffraction method or measurement of the particle size observed by SEM.
The specific surface area of the Al ₂ O ₃ powder used as the raw material is desirably ^{2 to} 30 m ² / g.

When Al ₂ O ₃ powder having a specific surface area of less than 2 m ² / g is used, sintering with Al ₂ O ₃ hardly occurs in the heating process, so that it tends to be distorted in the process of nitriding or sintering of AlN. , Particles of high circularity cannot be obtained.

Also, if the specific surface area was used 30 m ² / g greater than Al ₂ O ₃ particles, since the sintering at a temperature lower than the Atsushi Nobori process and nitriding occurs temperature likely to proceed, the Al ₂ O ₃ granulated powder The pores on the surface are blocked, and nitrogen necessary for nitriding inside is not supplied, resulting in particles with low AlN conversion, which is not desirable.

  The surface area can be measured by a BET specific surface area measurement method specified in JIS-Z8830.

(La, Dy, Er compounds)
As the compounds of La, Dy, and Er used as the raw materials, oxides, carbonates, oxa oxides, chlorides, nitrates, alkoxides, and the like can be used.
In particular, an inexpensive and stable oxide powder can be used, and the use of a fine oxide powder having a particle size of 1 μm or less uniformly sinters the granulated powder and sinters after AlN conversion. Spherical AlN particles having a high degree and a high AlN content can be obtained. Since the mixing ratio is small, the lower limit of the particle size is not particularly limited.

(Si compound)
As the Si compound used as a raw material, silicon alkoxides such as SiO ₂ and tetramethoxysilane, colloidal silica, and the like can be used. When SiO ₂ is used, its structure is not limited, such as amorphous, quartz, cristobalite, etc., but by using fine SiO ₂ powder of 1 μm or less, sintering of Al ₂ O ₃ in the granulated powder occurs uniformly. Therefore, spherical AlN particles having a high circularity and a high AlN content can be obtained. Since the mixing ratio is small, the lower limit of the particle size is not particularly limited.

(Mixing / granulation)
Any method of mixing the Al ₂ O ₃ powder, which is a raw material, with the compounds of La, Dy, and Er, and the Si compound may be used as long as the method is a uniform mixing method. The mixing can be performed by dry mixing or wet mixing using a solvent such as water, alcohol, or acetone.

As a method of granulating the mixed powder into a sphere, a method such as spray drying, tumbling granulation, stirring granulation, and flow granulation can be used.
In particular, when the spray drying method is used, a large amount of raw material powder can be efficiently granulated into a sphere. In the case of performing granulation by spray drying, by using an additive such as a dispersant or a binder in a solvent such as water, the raw materials are uniformly dispersed, and a granulated powder having high strength can be obtained.

  Further, since the spherical AlN particles obtained by nitriding are almost the same as the particle diameter of the granulated powder, by controlling the particle diameter of the granulated powder, spherical AlN particles having a desired particle diameter can be obtained.

<About nitridation reduction>
(Carbon mixture)
In addition, spherical AlN particles having a higher AlN content can be obtained by mixing the spherically granulated powder and the carbon powder and nitriding at a high temperature.

  As the carbon powder, any form of carbon powder such as activated carbon, graphite, and amorphous carbon may be used.

  By mixing and heat-treating the carbon powder with the granulated powder, the presence of the carbon powder between the granulated powders can suppress the bonding of the granulated powders due to sintering or fusion, When mixed with a resin, spherical AlN particles having a high degree of circularity and capable of being highly filled can be obtained.

Further, by adding carbon, reductive nitridation of Al ₂ O ₃ is promoted, and spherical AlN particles having a high AlN content can be obtained.

The carbon powder is desirably mixed in an amount 0.5 times or more the amount necessary for reducing all the O in Al ₂ O ₃ as CO ₂ . When the amount of carbon is less than 0.5 times, the amount of reduction of Al ₂ O ₃ is reduced, and accordingly, the ratio of nitriding to AlN is reduced, thereby obtaining particles having the target AlN content. Can not. Although there is no particular upper limit on the addition ratio of carbon, a sufficient effect can be obtained within 5 times the amount required for reducing Al ₂ O ₃ .

In the case of directly nitriding Al ₂ O ₃ , NH ₃ gas or H ₂ gas can be used. However, when an inexpensive and safe N ₂ gas is used as a nitrogen source, a nitriding reaction is unlikely to occur, and carbon is added to reduce nitrogen. By nitriding, Al ₂ O ₃ can be efficiently converted to AlN.

Carbon, and reduced in contact with the Al ₂ O _3, is effective to promote nitridation by N ₂ gas, spherical AlN particles according to the invention since progressed nitride at grain interior, carbon and Al ₂ O ₃ It is considered that CO gas is generated by the catalytic reduction, and the CO gas also contributes to the reduction of Al ₂ O ₃ and promotes the nitriding reaction.

(Heat treatment)
By subjecting the spherical granulated powder to heat treatment at a temperature of 1400 to 1800 ° C. in a nitrogen-containing atmosphere, spherical AlN particles can be obtained. The temperature during the heat treatment is measured by a radiation thermometer.

At a temperature lower than 1400 ° C., nitridation of Al ₂ O ₃ hardly occurs, and particles having a low AlN content are not desirable. If the heat treatment is performed at a temperature higher than 1800 ° C., the spherical AlN particles formed by nitriding start to sinter, and the particles are bonded to each other or decomposition of the AlN particles starts, which is not desirable.

  As a heating method of the heat treatment for nitriding the granulated powder, for example, the granulated powder is put into a container such as a carbon crucible, and resistance heating using a carbon heater or the like, or heating from the outside of the container by high-frequency induction heating. It can be heated by external heating.

  In addition, when nitriding the granulated powder, by using a method of heating by microwaves, it is possible to uniformly heat the powder placed in a container such as a crucible to the inside, lower temperature than normal heat treatment by external heating, and Spherical AlN particles can be obtained in a short time.

  When spherical AlN particles are obtained using microwave heating, a mixture of spherically granulated powder and carbon powder is irradiated with microwaves, so that carbon with high microwave absorption efficiency acts as a heat source. Thus, spherical AlN particles can be obtained more efficiently.

<About carbon removal processing>
When spherical AlN particles are produced by adding carbon powder, carbon can be oxidized and removed by heating to a temperature of 400 to 1000 ° C. in an oxidizing atmosphere such as air in order to remove carbon. At this time, by performing a heat treatment in an oxidizing atmosphere, the surface of the spherical AlN particles is oxidized to form an oxide layer, and thus an effect of preventing AlN from directly reacting with moisture or the like can be obtained.
Also, at this time, since the AlN particles are dense, the thickness of the surface oxide layer is as thin as about 1 μm, and there is almost no influence on the decrease in the ratio of AlN.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. However, the present invention is not construed as being limited to the following examples.

(Example 1)
As shown in Table 1, a mixture of Al ₂ O ₃ powder, SiO ₂ powder, various rare earth oxide powders, a PVA-based binder, a polycarboxylic acid-based dispersant, and water, and mixing with a ball mill was granulated by spray drying. did. A mixture obtained by mixing the obtained granulated powder and activated carbon (average particle size: 5 μm) at a weight ratio of 2: 1 was put in an alumina crucible, and heated at 1600 ° C. for 3 hours in a nitrogen atmosphere using a microwave. The temperature at this time was measured by a radiation thermometer. This was heat-treated at 600 ° C. in the air to oxidize and remove carbon to obtain spherical AlN particles.
The average particle size (D50) of the obtained spherical AlN particles was measured by a laser diffraction scattering type particle size distribution analyzer “CILAS 920” manufactured by Cirrus. The circularity was measured using a flow particle image analyzer “FPIA-2100” manufactured by Sysmex.

The content of AlN was determined by measuring an X-ray diffraction pattern using an Rigaku X-ray diffractometer “RINT-2500 TTR”. The calculation of the AlN content ratio measures the maximum peak intensity of AlN (PDF card No. 25-0133), Al ₂ O ₃ (PDF card No. 10-0173), and AlON (PDF card No. 48-0686). The AlN content was calculated as a percentage from the intensity ratio.

The spherical AlN particles according to the present invention exhibited a high circularity of 0.95 to 0.98, a high AlN content of 96 to 97%, and a high relative density to the calculated theoretical density of 96% or more.
On the other hand, those outside the range of the present invention had low circularity of 0.87 to 0.93 and low AlN content of 75 to 84%.

  In addition, in order to confirm the state of nitriding, the obtained spherical AlN particles were buried in a resin and polished, and the element distribution of the particle cross-section was measured using JEOL's electron probe microanalyzer (EPMA) “JXA-8230”. The mapping was measured.

  As a result, as shown in FIG. In three samples, almost no O (oxygen) was found inside the particles, N (nitrogen) was distributed throughout the particles, and it was confirmed that almost all the particles were AlN.

  On the other hand, in the sample of the comparative example, No. 1 shown in FIG. N was distributed only around the particles as in the four samples, and almost O remained inside the particles, confirming that nitriding occurred only on the surface.

Claims (6)

A spherical particle containing at least one compound of La, Dy, and Er, a compound of Si, and AlN,
0 relative to the weight 100 wt% of the whole grain, said La, Dy, any one or more compounds of Er total 0.01-0.5% in terms of oxide, a compound of the Si in terms of SiO _2. 01-0.5 wt%, containing the AlN in a proportion of 80 wt% or more,
Has a relative density of 90% or more of the theoretical density,
Spherical AlN particles having a circularity of 0.85 to 1.00. A spherical AlN filler comprising a plurality of the spherical AlN particles according to claim 1,
A spherical AlN filler having an average particle diameter (D50) of 5 to 150 μm. A method for producing spherical AlN particles according to claim 1,
A raw material powder mixing step of mixing an Al ₂ O ₃ powder having an average particle size of 0.05 to 4 μm with a powder of at least one compound of La, Dy, and Er and a powder of a compound of Si;
A granulation step of granulating the mixture produced in the raw material powder mixing step into a sphere,
A carbon powder mixing step of mixing the spherical granules produced in the granulation step with carbon powder,
A nitriding step of heat-treating and nitriding the mixture generated in the carbon powder mixing step at a temperature of 1400 to 1800 ° C. in a nitrogen atmosphere.
In the raw material powder mixing step, the ratio of the compound after mixing is 0.008 wt.% In terms of oxides by dividing the powder of at least one of La, Dy, and Er into 100 wt% of Al ₂ O ₃ powder. ～0.565Wt%, and, 0.008～0.565Wt% said compound of Si in terms of SiO _2, characterized by mixing to contain, method for producing spherical AlN particles.   The method for producing spherical AlN particles according to claim 3, wherein in the granulation step, granulation is performed by a spray drying method.   The method for producing spherical AlN particles according to claim 3, wherein the heat treatment is performed by microwave in the nitriding step.   The method for producing spherical AlN particles according to any one of claims 3 to 5, wherein the temperature of the heat treatment in the nitriding step is 1600 to 1800 ° C.