JP7626801B2 - Aluminum nitride powder, its modification method, and polymer molded body - Google Patents

Description

The present invention relates to aluminum nitride powder.

Taking advantage of its excellent thermal conductivity, aluminum nitride powder is used as a filler to be mixed into materials such as resins, greases, adhesives, and paints. The material properties required of a filler include filling ability, kneadability, and thermal conductivity, and various efforts are being made to improve the material properties.

Previously, in Patent Document 1, the applicant reported that highly spherical aluminum nitride powder, in which 70% or more of the particles have an outer periphery that does not include sharp corners or unevenness, can improve filling properties, kneading properties, and thermal conductivity.

Furthermore, in Patent Document 2, the applicant reported that fluidity and filling properties can be improved by using spherical aluminum nitride powder with a median diameter (D50) of 1.9 to 4.0 μm, 10% or less of particles with a particle diameter of 0.9 μm or less, 10% or less of particles with a particle diameter of 7 μm or more, and a sphericity of 0.8 or more.

The spherical aluminum nitride powders in Patent Documents 1 and 2 are basically produced by adding and mixing rare earth compound powder, calcium compound powder, and carbon powder to aluminum nitride raw material powder, heat treating the mixture in a non-oxidizing atmosphere to promote particle spheroidization and growth, and then heat treating the mixture in an oxidizing atmosphere to decarburize the particles.

Next, Patent Document 3 states the general theory that if coarse particles are contained in the filler, clogging occurs when filling gaps, resulting in uneven filling, voids, and molding defects, and that the presence of agglomerated particles can cause poor flowability. It then states that no aluminum nitride powder with controlled amounts of coarse particles or agglomerated particles has been reported, and reports an aluminum nitride powder that has been classified by removing excess coarse particles.

Regarding classification, Patent Document 3 states that various methods such as dry methods (sieve classification, air classification) and wet methods (wet filter classification, fluid classification) can be used, but air classification and wet classification are more efficient at removing coarse particles, and further states that wet classification leaves fewer coarse particles after classification than air classification, and that wet filter classification has better accuracy and higher productivity than fluid classification, and in the examples only wet filter classification is used. Wet filter classification is a classification method in which powder is dispersed in a solvent, deagglomerated, and then passed through a filter.

Patent No. 6700460 Patent No. 7149379 Patent No. 7017556

However, the aluminum nitride powders in Patent Documents 1 and 2 produced by the above methods left room for improvement in terms of wettability with polymeric materials such as resins.

The inventors of the present application believed that wet classification of aluminum nitride powder as in Patent Document 3 could affect the wettability with polymeric materials such as resins, and when they carried out a follow-up test of the aluminum nitride powder in the examples of Patent Document 3, they found that the wettability with polymeric materials such as resins was worse after classification than before classification (see the oil absorption amounts of Comparative Examples 2 and 4 described below).

The object of the present invention is to provide an aluminum nitride powder that has excellent wettability with polymeric materials such as resins.

The inventors further investigated whether it would be possible to improve the wettability of aluminum nitride powder with polymeric materials such as resins by changing the particle surface condition of the aluminum nitride powder. As a result, they discovered that it is possible to improve the wettability of aluminum nitride powder with polymeric materials such as resins by subjecting the aluminum nitride powder to a specific dry classification, and after further investigations they arrived at the present invention.

[1] Aluminum nitride powder with an oil absorption of 13.5 g/100 g or less based on the refined linseed oil method in accordance with JIS K5101-13-1:2004.

The oil absorption amount based on the refined linseed oil method according to JIS K5101-13-1:2004 (ISO 787-5:1980) is calculated by dropping a small amount of silicone oil to 10g of powder, kneading with a spatula, spreading it without breaking or crumbling, and dropping an amount that is lightly attached to a measuring plate, and converting it to the amount dropped per 100g of powder. The silicone oil used is KF96-300CS manufactured by Shin-Etsu Chemical Co., Ltd. The measured value of oil absorption is measured 10 times and the average value is used.
The smaller the oil absorption value, the better the wettability of the powder with oil, and the better the wettability with polymeric materials such as resins.
It is more preferable that the oil absorption is less than 13.0 g/100 g.

[2] The aluminum nitride powder described in [1] above, having a median diameter (D50) of 1.5 to 10 μm.

If the median diameter (D50) is less than 1.5 μm, agglomerated particles are likely to occur, making it difficult to use as a heat dissipating filler. If the median diameter (D50) is more than 10 μm, it becomes difficult to form a thin layer of the polymer molded article.

[3] Aluminum nitride powder having a median diameter (D50) of 1.5 to 10 μm and a rising tangent angle on the small diameter side of the particle size distribution curve of 45° or more.

The median diameter (D50) is as described above.
The rising tangent angle on the small diameter side of the particle size distribution curve is the angle formed by the rising tangent and the x-axis (logarithmic axis of particle diameter), and is calculated by the procedure described below. If this rising tangent angle is 45° or more, the number of fine crushed particles is small, and the wettability with polymer materials such as resins is improved.
This rising tangent angle is preferably 50° or more, and more preferably 55° or more.

[4] A polymer molded body in which the aluminum nitride powder described in any one of [1] to [3] above is filled into a polymer material.

[5] A method for modifying aluminum nitride powder, comprising classifying the aluminum nitride powder using a dry jet mill.
[6] A method for modifying an aluminum nitride powder, comprising classifying the aluminum nitride powder using a dry jet mill so that the oil absorption of the aluminum nitride powder based on the refined linseed oil method in accordance with JIS K5101-13-1:2004 is 89.5% or less after classification compared to before classification.

By classifying the aluminum nitride powder using a dry jet mill, not only is the aggregated powder broken down/pulverized, resulting in a reduction in Dmax and a sharpening of the particle size distribution, but also, because the collection method of the dry jet mill is a cyclone, fine crushed particles are less likely to be included in the classified powder, and the oil absorption is reduced, improving the wettability with polymeric materials such as resins.
Although wet classification allows for adjustment of particle size distribution equivalent to that achieved by dry jet mill classification, the oil absorption does not decrease.
The reason why there is a difference in oil absorption despite the same particle size distribution is currently unknown, but it is thought that this is because the state of the particle surface newly exposed by crushing or pulverization using a dry jet mill is different from the state of the surface that was originally exposed.

The present invention provides aluminum nitride powder that has high wettability with polymeric materials such as resins.

1A is a SEM photograph of the aluminum nitride powder of Example 1 at a magnification of 100 times, and FIG. 1B is a SEM photograph at a magnification of 2000 times. 2A is a SEM photograph of the aluminum nitride powder of Comparative Example 1 at a magnification of 100 times, and FIG. 2B is a SEM photograph of the aluminum nitride powder of Comparative Example 1 at a magnification of 2000 times. 3A is a SEM photograph of the aluminum nitride powder of Comparative Example 2 at a magnification of 100 times, and FIG. 3B is a SEM photograph of the aluminum nitride powder of Comparative Example 2 at a magnification of 2000 times. FIG. 4 is a graph showing particle size distribution curves of Examples 1, 2, and 3 and Comparative Examples 1 and 2 (A-02-F system), and FIG. 4 is an enlarged view of the rising edge of FIG. FIG. 5 is a graph showing particle size distribution curves of Examples 4 and 5 and Comparative Examples 3 and 4 (A-05-F system), and FIG. 5 is an enlarged view of the rising edge of (a).

<1> Composition of Aluminum Nitride Powder (a) The composition of the aluminum nitride powder is not particularly limited, but in addition to aluminum nitride, it may contain a rare earth compound derived from the production method, and may further contain a calcium compound.

There are no particular limitations on the rare earth compound, but it is preferable that the amount is 3.0 mass% or less in terms of oxide relative to 100 mass% of aluminum nitride. If the rare earth compound exceeds 3.0 mass%, the purity of the aluminum nitride decreases, and there is a concern that the thermal conductivity may decrease.

Rare earth compounds include, but are not limited to, oxides or halides of Y, Yb, La, Nd, and Sm.

There are no particular limitations on the calcium compound, but it is preferable that the amount is 0.5 mass% or less in terms of oxide relative to 100 mass% of aluminum nitride. If the calcium compound exceeds 0.5 mass%, the purity of the aluminum nitride decreases, and there is a concern that the thermal conductivity will decrease.

(A) Manufacturing Method The manufacturing method of the aluminum nitride powder (before the dry jet mill treatment) is not particularly limited, and a commercially available product may be used. Examples of the manufacturing method include the manufacturing methods described in Patent Document 1 or Patent Document 2.

(c) Classification by dry jet mill (modification method) Classification by dry jet mill involves ejecting gas from an ejection nozzle, accelerating the raw material particles with the jet stream, and pulverizing them by particle collision and grinding. There are no particular limitations on the dry jet mill device used for this, and any publicly known or commercially available dry jet mill device can be used.

<2> Polymer Molded Articles The aluminum nitride powder of the present invention can be used to prepare polymer molded articles having high thermal conductivity by filling them into polymer materials. Examples of polymer materials include resins, rubbers, elastomers, etc.

<3> Uses Uses of the aluminum nitride powder are not particularly limited, but examples include fillers to be mixed into materials such as polymer materials, greases, adhesives, and paints.
Applications of polymer molded articles obtained by filling a polymer material with the aluminum nitride powder of the present invention as a filler are not particularly limited, and examples thereof include circuit boards used in semiconductor modules, LED packages, Peltier modules, printers, multifunction machines, semiconductor lasers, optical communications, high frequencies, and the like, general-purpose heat dissipation members, heat dissipation members (heat sinks) for power semiconductor modules, insulating plates, and the like.

Next, examples of the present invention will be described with reference to the drawings, in comparison with comparative examples. Note that the materials, quantities, and conditions of each part in the examples are merely examples, and may be modified as appropriate without departing from the spirit of the invention.

As shown in Table 1, "A-02-F" manufactured by Maruwa Corporation (applicant of the present application) was used as the aluminum nitride powder starting material in Examples 1, 2, and 3 and Comparative Examples 1 and 2, while "A-05-F" manufactured by the same company was used in Examples 4 and 5 and Comparative Examples 3 and 4. Hereinafter, the term "each example" refers to each of Examples 1 to 5 and Comparative Examples 1 to 4.

- In Examples 1, 2, and 3, "A-02-F" was classified using a dry jet mill "PJM-80" manufactured by Nippon Pneumatic Mfg. Co., Ltd. The grinding pressure was 0.4 MPa in Example 1, 0.3 MPa in Example 2, and 0.2 MPa in Example 3. The raw material supply amount (processing amount) was 300 g/hr. The number of grinding passes was one pass. The atmosphere of the entire line was air. The collection method for the dry jet mill is a cyclone, so it has the characteristic that particularly fine crushed particles are removed and not included in the powder after classification.

Comparative Example 1 uses "A-02-F" as is, without classification.

- Comparative Example 2 was obtained by dispersing "A-02-F" in IPA and leaving it to stand to allow the aggregated particles and coarse particles to settle, and then recovering the supernatant, filtering, and drying. At this time, the standing time was adjusted so that the D50 of Comparative Example 2 was close to the D50 of Examples 1, 2, and 3.

- In Examples 4 and 5, "A-05-F" was classified using the dry jet mill "PJM-80" described above, and the grinding pressure was 0.4 MPa in Example 4 and 0.3 MPa in Example 5. The raw material supply amount (processing amount) was 300 g/hr. The number of grinding passes was one pass. The atmosphere of the entire line was air. The collection method was a cyclone.

- Comparative Example 3 uses "A-05-F" as is, without classification.

- Comparative Example 4 was obtained by dispersing "A-05-F" in IPA and leaving it to stand to allow the aggregated particles and coarse particles to settle, and then recovering the supernatant, filtering, and drying. At this time, the standing time was adjusted so that the D50 of Comparative Example 4 was close to the D50 of Examples 4 and 5.

The following observations and measurements were carried out on the aluminum nitride powder obtained for each example.

(1) Observation of SEM photographs FIG. 1 is an SEM photograph of the aluminum nitride powder of Example 1, FIG. 2 is an SEM photograph of the aluminum nitride powder of Comparative Example 1, and FIG. 3 is an SEM photograph of the aluminum nitride powder of Comparative Example 2, where (a) is a magnification of 100 times and (b) is a magnification of 2000 times.

Compared to Comparative Examples 1 and 2, Example 1 has smaller variation in particle size of the aluminum nitride powder and fewer agglomerates.

(2) Particle size distribution 0.5 g of aluminum nitride powder of each example was added to 50 ml of 0.1% by mass aqueous sodium pyrophosphate solution, and dispersed for 3 minutes at 80% output using a US-300E model manufactured by Nippon Seiki Seisakusho Co., Ltd. The volume-based particle size distribution of the dispersion was measured using a laser diffraction particle size distribution measuring device, SALD-2200 model manufactured by Shimadzu Corporation. The measurement results are shown in Table 1, Figures 4 and 5. Dmax = D99.99.

"A-02-F" originally mainly contains 2 μm particles, but as shown in the particle size distribution in Figure 4(a), the peak top of Comparative Example 1 is at 3 to 4 μm. This is due to some of the 2 μm particles agglomerating.
The peak top shifted to about 3 μm in Comparative Example 2 because agglomerated particles and coarse particles were removed by wet classification. The peak top shifted to 2-3 μm in Examples 1-3 because agglomerated particles were disintegrated by the dry jet mill. However, the peak tops did not reach 2 μm or less in any of the examples, probably because no or little crushing of 2 μm particles occurred.

"A-05-F" originally mainly contains 4 μm particles, but as shown in the particle size distribution in Figure 5(a), the peak top of Comparative Example 3 is at 5.5 to 6 μm. This is due to some of the 4 μm particles agglomerating.
The peak top shifted to 4-5 μm in Comparative Example 4 because agglomerated particles and coarse particles were removed by wet classification, and the peak top shifted to about 4 μm in Examples 4 and 5 because agglomerated particles were disintegrated by the dry jet mill.

(3) (D90-D10)/D50
The calculation results of (D90-D10)/D50 are shown in Table 1. This value is an index of the sharpness of the particle size distribution, and the smaller the value, the sharper the particle size distribution.

Compared to Comparative Example 1, Comparative Example 2 and Examples 1 to 3 clearly had smaller values.
Compared to Comparative Example 3, Comparative Example 4 and Examples 4 and 5 have clearly smaller values.

(4) Rising tangent angle on the small diameter side The rising tangent angle on the small diameter side of the particle size distribution curve is the angle formed by the rising tangent shown in Fig. 4(b) and Fig. 5(b) and the x-axis (logarithmic axis of particle diameter), and was calculated by the following procedure.
i) Two plotted points at the beginning of the small diameter side of the particle size distribution curve are read and designated as (x1, y1) and (x2, y2).
Here, x is the particle diameter, y is the relative particle amount, and y1=0.
x2 is an arbitrary point in the range where logx2-logx1 satisfies 0.040-0.050. The second point (x2, y2) that was actually read is indicated by an arrow in Figures 4(b) and 5(b).
ii) If the line connecting the two points is regarded as a tangent to the particle size distribution curve, the slope of the tangent is y2/(x2-x1).
iii) Take tan ⁻¹ for the slope of the tangent line to calculate the angle of the tangent line.
The calculation results are shown in Table 1.

Compared to Comparative Example 1, the increase in the tangent angle in Comparative Example 2 is slight, but the increase in the tangent angle in Examples 1 to 3 is very large.
Compared to Comparative Example 3, the increase in the tangent angle in Comparative Example 4 is slight, but the increases in the tangent angle in Examples 4 and 5 are very large.
The results of Examples 1 to 5 show that, since the collection method of the dry jet mill is a cyclone as described above, particularly fine crushed particles are removed and are not included in the powder after classification.

(5) Oil Absorption The oil absorption was measured based on the refined linseed oil method in accordance with JIS K5101-13-1:2004.

Compared to Comparative Example 1, Comparative Example 2 had a larger oil absorption amount, whereas Examples 1 to 3 had smaller oil absorption amounts.
Compared to Comparative Example 3, Comparative Example 4 had a larger oil absorption amount, whereas Examples 4 and 5 had smaller oil absorption amounts.
As mentioned above, the details of the results of Examples 1 to 5 are unclear at present, but it is believed that this is because the particle surface state newly exposed by crushing or pulverization using a dry jet mill is different from the surface state originally exposed. Thus, by using an aluminum nitride powder having an oil absorption of 9.0 g/100 g to 13.5 g/100 g based on the refined linseed oil method in accordance with JIS K5101-13-1:2004 as a filler in a polymer material such as a resin, the wettability was good and the kneadability was improved.

The present invention is not limited to the above-mentioned examples, and can be modified as appropriate without departing from the spirit of the invention.

Claims (5)

Aluminum nitride powder with an oil absorption of less than 13.0 g/100 g based on the refined linseed oil method in accordance with JIS K5101-13-1:2004. The aluminum nitride powder according to claim 1, having a median diameter (D50) of 1.5 to 10 μm. Aluminum nitride powder with a median diameter (D50) of 1.5 to 10 μm and a rising tangent angle on the small diameter side of the particle size distribution curve of 45° or more. A polymer molded body in which the aluminum nitride powder according to any one of claims 1 to 3 is filled into a polymer material. A method for modifying aluminum nitride powder in which the aluminum nitride powder is classified using a dry jet mill so that the oil absorption after classification is 89.5% or less of the amount before classification based on the refined linseed oil method in accordance with JIS K5101-13-1:2004.

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