JP2012171842A - Composite particle of melamine borate and boron nitride, and method for producing boron nitride particle using the same - Google Patents
Composite particle of melamine borate and boron nitride, and method for producing boron nitride particle using the same Download PDFInfo
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本発明は、熱伝導性に優れた窒化ホウ素粒子、及びその製造方法に関する。 The present invention relates to boron nitride particles having excellent thermal conductivity and a method for producing the same.
近年、半導体素子をはじめとする発熱性電子部品の高密度化が進み、体面積あたりの発熱量が増加している。そのため、電子部品の動作特性や信頼性等を保つ上で放熱特性に優れた材料が求められている。このような背景により、高熱伝導性を有し、化学的・熱的に安定な窒化ホウ素が着目され、熱伝導フィラーとして利用されることが進んでいる。 In recent years, the density of heat-generating electronic components such as semiconductor elements has increased, and the amount of heat generated per body area has increased. Therefore, a material excellent in heat dissipation characteristics is required in order to maintain the operation characteristics and reliability of electronic parts. With this background, boron nitride having high thermal conductivity and being chemically and thermally stable is attracting attention and is being used as a thermal conductive filler.
しかし、窒化ホウ素粉末は、結晶構造と鱗片形状に由来する熱伝導の異方性が大きいため、フィラーとして樹脂に充填した際、樹脂中での粒子の配向に起因する熱伝導の低下が懸念されてきた。これを改善するため、製造方法を工夫するなどして、一次粒子の配向を抑制した種々の造粒粒子が提案されている。 However, since boron nitride powder has a large thermal anisotropy derived from the crystal structure and scale shape, there is a concern that when the resin is filled as a filler, the thermal conductivity is reduced due to the orientation of the particles in the resin. I came. In order to improve this, various granulated particles in which the orientation of primary particles is suppressed have been proposed by devising the production method.
窒化ホウ素造粒粒子の作成方法としては、(1)有機・無機バインダー成分により一次粒子同士を接着する方法。(2)窒化硼素焼結体を製造し、これを粉砕、分級する方法。(3)結晶成長（高温焼成）過程にて、結晶成長条件（焼成条件）を制御し製造する方法などが挙げられる。これらの手法を用いた場合、(1)では窒化ホウ素が鱗片形状であるため、造粒した際に一次粒子間に隙間を生じやすく粗構造となり易い（特許文献１）。(2)、(3)では、形状制御が難しいなどの問題があった（特許文献２〜３）。本発明は、上記の問題点を解決する新たな造粒粒子製造プロセスである。 As a method for producing boron nitride granulated particles, (1) a method in which primary particles are bonded to each other with an organic / inorganic binder component. (2) A method in which a boron nitride sintered body is produced, and pulverized and classified. (3) In the crystal growth (high-temperature firing) process, a method of manufacturing by controlling the crystal growth conditions (firing conditions), and the like. When these methods are used, in (1), since boron nitride has a scaly shape, a gap is easily formed between primary particles when granulated (patent document 1). In (2) and (3), there is a problem that shape control is difficult (Patent Documents 2 to 3). The present invention is a new granulated particle production process that solves the above problems.
本発明の目的は、熱伝導性に優れた窒化ホウ素粒子を提供することである。 An object of the present invention is to provide boron nitride particles having excellent thermal conductivity.
すなわち、本発明は上記の課題を解決するために、以下の手段を採用する。
（１）ホウ酸メラミンと、粉末X線回折法による黒鉛化指数（ＧＩ）２．０以下、平均粒子径５〜４０μmの鱗片状窒化ホウ素粉末からなり、平均粒子径が４０〜３００μmである複合粒子。
（２）有機バインダーを０．０５〜１．０質量％含有した水溶液１００質量部に対し、ホウ酸メラミン１００質量部に対して鱗片状窒化ホウ素が１．０〜２０質量部の混合物１０〜５０質量部含有するスラリーを用いて、噴霧造粒することを特徴とする前記（１）記載の複合粒子の製造方法。
（３）前記（１）に記載の複合粒子を、非酸化性雰囲気下６００〜１３００℃で焼成後、非酸化性雰囲気下１６００〜２２００℃で焼成する窒化ホウ素粒子の製造方法。
That is, the present invention employs the following means in order to solve the above problems.
(1) A composite composed of melamine borate and a scaly boron nitride powder having a graphitization index (GI) of 2.0 or less and an average particle diameter of 5 to 40 μm by a powder X-ray diffraction method, and having an average particle diameter of 40 to 300 μm particle.
(2) 10 to 50 mixture of 1.0 to 20 parts by weight of flaky boron nitride with respect to 100 parts by weight of melamine borate with respect to 100 parts by weight of an aqueous solution containing 0.05 to 1.0% by weight of an organic binder The method for producing composite particles according to (1) above, wherein spray granulation is performed using a slurry containing part by mass.
(3) A method for producing boron nitride particles, wherein the composite particles according to (1) are fired at 600 to 1300 ° C. in a non-oxidizing atmosphere and then fired at 1600 to 2200 ° C. in a non-oxidizing atmosphere.
ホウ酸メラミンと鱗片状窒化ホウ素を噴霧造粒により複合することで、球形の複合粒子を形成することができる。そのため、この造粒粒子を焼成して得られる窒化ホウ素粒子は、球形に近い形状となり、流動性に優れている。このような特徴を有する窒化ホウ素粒子を熱伝導フィラーとして使用すると、充填性が良好であるため、効率的な熱伝導を実現できる。 Spherical composite particles can be formed by combining melamine borate and flaky boron nitride by spray granulation. Therefore, boron nitride particles obtained by firing the granulated particles have a shape close to a sphere and are excellent in fluidity. When boron nitride particles having such characteristics are used as a heat conductive filler, since the filling property is good, efficient heat conduction can be realized.
以下、さらに詳しく本発明について説明する。
本発明の複合粒子並びにそれを焼成してなる窒化ホウ素粒子は、鱗片状窒化ホウ素が形成する隙間にホウ酸メラミンが存在することが重要である。また、ホウ酸メラミンが核として存在した場合さらに好適である。
Hereinafter, the present invention will be described in more detail.
It is important that the composite particles of the present invention and the boron nitride particles obtained by firing the particles have melamine borate in the gaps formed by the scaly boron nitride. Further, it is more preferable when melamine borate is present as a nucleus.
ここでホウ酸メラミンとは、ホウ酸分子とメラミン分子が水素結合で結ばれた付加化合物であり、理論上２モルのホウ酸と１モルのメラミンから形成される。メラミンは３００℃付近で昇華性を有しているが、このホウ酸メラミンを形成するとメラミンの昇華が抑制される。つまり単なるホウ酸とメラミンの混合物を用いるより窒化ホウ素の生成率が向上するため、複合粒子を焼成して得られる窒化ホウ素粒子は緻密質となり易い。なおホウ酸メラミンの存在は、Ｘ線回折測定により確認することができる（ホウ酸、メラミンと比較して、２θ＝２３．３°に固有のピークを有する）。また、メラミンの昇華は、熱重量分析の３００℃付近の質量減少の有無によって確認することができる。
なお、平均粒径１〜３０μｍと比較的粒径の小さいホウ酸メラミンを用いると、複合粒子が調製し易い。
Here, melamine borate is an addition compound in which boric acid molecules and melamine molecules are bonded by hydrogen bonds, and is theoretically formed from 2 mol of boric acid and 1 mol of melamine. Melamine has sublimability at around 300 ° C., but when this melamine borate is formed, sublimation of melamine is suppressed. That is, since the formation rate of boron nitride is improved more than using a simple mixture of boric acid and melamine, the boron nitride particles obtained by firing the composite particles tend to be dense. The presence of melamine borate can be confirmed by X-ray diffraction measurement (having a specific peak at 2θ = 23.3 ° compared to boric acid and melamine). Moreover, the sublimation of melamine can be confirmed by the presence or absence of mass reduction around 300 ° C. in thermogravimetric analysis.
If melamine borate having an average particle size of 1 to 30 μm and a relatively small particle size is used, composite particles can be easily prepared.
一般的に、窒化ホウ素は特異的な鱗片形状を有するため、前述のとおり鱗片状窒化ホウ素粒子のみで造粒を行っても、緻密な粒子を作製することは困難である。緻密化した球形造粒粒子を作製するためには、鱗片状窒化ホウ素が形成する空隙をホウ酸メラミンで埋めることが重要である。更に造粒を高熱伝導化させるためには、鱗片状窒化ホウ素に近接したホウ酸メラミンが最終的に窒化ホウ素となり、かつ粒子がランダム配向していることが望ましい。 In general, since boron nitride has a specific scale shape, it is difficult to produce dense particles even if granulation is performed using only scale-like boron nitride particles as described above. In order to produce densified spherical granulated particles, it is important to fill voids formed by scaly boron nitride with melamine borate. Furthermore, in order to increase the thermal conductivity of the granulation, it is desirable that melamine borate in the vicinity of the flaky boron nitride eventually becomes boron nitride and the particles are randomly oriented.
つまり、高熱伝導性鱗片状窒化ホウ素粒子にホウ酸メラミンが近接して存在する複合粒子を作製し、これを焼成することで、(1)緻密、(2)球形、(3)ランダム配向、を満たし、ひいては高熱伝導性を示す窒化ホウ素粒子が作製される。このような知見に立った窒化ホウ素粒子は今まで見られない。 In other words, by producing composite particles in which melamine borate is present close to highly heat-conductive flaky boron nitride particles and firing this, (1) dense, (2) spherical, (3) random orientation, Boron nitride particles that fill and thus exhibit high thermal conductivity are produced. Boron nitride particles based on such knowledge have not been seen so far.
なお本発明の窒化ホウ素粒子は、一般的に樹脂などと混合されてなる複合材料として用いられる。この混合の際に窒化ホウ素粒子が崩壊すると当然高熱伝導性は望めないため、粒子自体に強度が求められる。しかし本発明の窒化ホウ素粒子はその緻密な構造により十分な強度を有しているため、このような問題は生じない。なお窒化ホウ素粒子の強度の測定方法としては、ＪＩＳ Ｒ １６３９−５（ファインセラミックス―か（顆）粒特性の測定方法―第５部：単一か粒圧壊強さ）などに示されている。 The boron nitride particles of the present invention are generally used as a composite material mixed with a resin or the like. If boron nitride particles collapse during this mixing, naturally high thermal conductivity cannot be expected, so the strength of the particles themselves is required. However, since the boron nitride particles of the present invention have sufficient strength due to their dense structure, such a problem does not occur. The method for measuring the strength of the boron nitride particles is shown in JIS R 1639-5 (Fine Ceramics-Method for Measuring (Condyle) Grain Properties-Part 5: Single Particle Crush Strength).
一般的に窒化硼素の製造では、結晶化を進めるために含硼素化合物、含窒素化合物に加えて第三成分が添加される。第三成分として主にアルカリ金属及びアルカリ土類金属の水酸化物、塩化物、炭酸塩、リン酸塩等が用いられる。本発明においては特に規定はしないが、炭酸カルシウム、水酸化カルシウムなどのカルシウム系化合物が結晶成長性等で好ましい。 In general, in the production of boron nitride, a third component is added in addition to a boron-containing compound and a nitrogen-containing compound in order to promote crystallization. As the third component, alkali metal and alkaline earth metal hydroxides, chlorides, carbonates, phosphates and the like are mainly used. Although not specified in the present invention, calcium compounds such as calcium carbonate and calcium hydroxide are preferable in terms of crystal growth.
本発明に用いられる鱗片状窒化ホウ素粉末は黒鉛化指数（ＧＩ）２．０以下、平均粒子径５〜４０μｍであるが、特に（ＧＩ）１．５以下、平均粒子径８〜２５μｍが好ましい。ＧＩ（Ｇｒａｐｈｉｔｉｚａｔｉｏｎ Ｉｎｄｅｘ）はＸ線回折図の（１００）、（１０１）及び（１０２）線の積分強度比すなわち面積比を、ＧＩ＝〔面積{（１００）＋（１０１）}〕／〔面積（１０２）〕、によって求めることがでる（Ｊ．Ｔｈｏｍａｓ，ｅｔ．ａｌ，Ｊ．Ａｍ．Ｃｈｅｍ．Ｓｏｃ．８４，４６１９（１９６２））。完全に結晶化したものでは、（ＧＩ）１．６０になるとされているが、高結晶性でかつ粒子が十分に成長した鱗片状窒化ホウ素粉末の場合、粒子が配向しやすいためＧＩはさらに小さくなる。すなわち、ＧＩは鱗片状窒化ホウ素の結晶性の指標であり、この値が小さいほど結晶性が高い。 The scaly boron nitride powder used in the present invention has a graphitization index (GI) of 2.0 or less and an average particle size of 5 to 40 μm, and (GI) of 1.5 or less and an average particle size of 8 to 25 μm are particularly preferable. GI (Graphization Index) is an integrated intensity ratio, that is, an area ratio of (100), (101) and (102) lines of an X-ray diffraction diagram, and GI = [area {(100) + (101)}] / [area ( 102)] (J. Thomas, et.al, J. Am. Chem. Soc. 84, 4619 (1962)). When fully crystallized, it is said that (GI) is 1.60. However, in the case of scaly boron nitride powder having high crystallinity and sufficiently grown particles, the GI is even smaller because the particles are easily oriented. Become. That is, GI is an index of crystallinity of scaly boron nitride, and the smaller this value, the higher the crystallinity.
そのため、ＧＩが２．０より大きい鱗片状窒化ホウ素粒子は結晶性が低いため、熱伝導率が低く、これを複合して、得られる造粒粒子の熱伝導率は低い。また、鱗片状窒化ホウ素粉末の平均粒子径が５μｍより小さいと、一次粒子同士の接点の増加にともなう接触抵抗の増加により熱伝導率が低下し、４０μｍより大きいと複合粒子の製造が困難となる。 Therefore, scaly boron nitride particles having a GI greater than 2.0 have low crystallinity and thus low thermal conductivity, and the thermal conductivity of the granulated particles obtained by combining them is low. Further, when the average particle diameter of the flaky boron nitride powder is smaller than 5 μm, the thermal conductivity is lowered due to an increase in contact resistance accompanying the increase in the contact between the primary particles, and when larger than 40 μm, it is difficult to produce composite particles. .
上記の原料から噴霧造粒法により複合粒子を製造することができる。粉末の造粒方法としては、転動造粒法、粉砕法、噴霧造粒法等あるが、その中でも噴霧造粒法は球形度の高い造粒粒子が得られるため、本発明の高熱伝導率を有する造粒粒子の製造方法としては好ましい。これら以外の造粒方法では球形度の高い造粒粒子は得られない。また、噴霧条件、及びスラリー粘度を調整することで粒径制御が可能であり、比較的粒径の揃った複合粒子を得ることができることもメリットである。 Composite particles can be produced from the above raw materials by spray granulation. Powder granulation methods include rolling granulation method, pulverization method, spray granulation method, etc. Among them, since the spray granulation method can obtain granulated particles with high sphericity, the high thermal conductivity of the present invention. This is preferable as a method for producing granulated particles. Granulation methods other than these cannot obtain granulated particles with high sphericity. Further, the particle size can be controlled by adjusting the spraying conditions and the slurry viscosity, and it is also advantageous that composite particles having a relatively uniform particle size can be obtained.
噴霧造粒に用いられるスラリーは、有機バインダーを０．０５〜１．０質量％含有した水溶液１００質量部に対し、ホウ酸メラミン１００質量部に対して鱗片状窒化ホウ素が１．０〜２０質量部の混合粉１０〜５０質量部を含有するものである。 The slurry used for spray granulation has a scale-like boron nitride of 1.0 to 20 mass per 100 mass parts of melamine borate with respect to 100 mass parts of an aqueous solution containing 0.05 to 1.0 mass% of an organic binder. 10 to 50 parts by mass of the mixed powder.
有機バインダーに関しては、ポリビニルアルコール系、ポリアクリル酸系、多糖類系等あるが、この中でも特に、分解温度が窒化ホウ素の反応温度付近である、ポリアクリル酸系が望ましい。有機バインダー濃度に関しては、溶媒に対して０．０５〜１．０質量％が好ましい。有機バインダーは、最終的には除去しなければならないため、使用するバインダーの種類によって最適量は異なるが、少なければ少ないほどよい。本発明においては、溶媒に対して、０．１〜０．５質量％添加することが特に好ましく、０．０５質量％より少ないと、バインダーとしての効果が小さく複合粒子が崩壊しやすい。また、１．０質量％より大きいと、不純物として残る可能性が高くなる。 Regarding the organic binder, there are polyvinyl alcohol, polyacrylic acid, polysaccharides, and the like. Among these, polyacrylic acid having a decomposition temperature close to the reaction temperature of boron nitride is particularly desirable. The organic binder concentration is preferably 0.05 to 1.0% by mass with respect to the solvent. Since the organic binder must be finally removed, the optimum amount varies depending on the type of binder used, but the smaller the better. In the present invention, it is particularly preferable to add 0.1 to 0.5% by mass with respect to the solvent. Moreover, when larger than 1.0 mass%, possibility that it will remain as an impurity will become high.
ホウ酸メラミンと鱗片状窒化ホウ素の配合比に関しては、ホウ酸メラミン１００質量部に対して鱗片状窒化ホウ素が１．０〜２０質量部であり、５．０〜１０質量部が好ましい。ホウ酸メラミンと鱗片状窒化ホウ素の配合比は、複合化および窒化ホウ素粒子の熱伝導率に影響を与える。すなわち、ホウ酸メラミン１００質量部に対して鱗片状窒化ホウ素が１．０質量部より少ないと、熱伝導率が低下し、２０質量部より多いと複合粒子の製造が困難となる。 Regarding the compounding ratio of melamine borate and flaky boron nitride, flaky boron nitride is 1.0 to 20 parts by weight, and preferably 5.0 to 10 parts by weight with respect to 100 parts by weight of melamine borate. The blending ratio of melamine borate and flaky boron nitride affects the composite and thermal conductivity of the boron nitride particles. That is, when the amount of flaky boron nitride is less than 1.0 part by mass with respect to 100 parts by mass of melamine borate, the thermal conductivity is lowered, and when it is more than 20 parts by mass, it is difficult to produce composite particles.
スラリー濃度に関しては、水溶液１００質量部に対して、ホウ酸メラミンと鱗片状窒化ホウ素からなる混合粉が１０〜５０質量部であり、２０〜４０質量部が好ましい。混合粉の濃度が５０質量部より大きい場合、スラリー粘度が上がり、噴霧が困難となる。混合粉の濃度が１０質量部より小さいと、噴霧直前に形成される粒子の含水率が高いため、乾燥して得られる複合粒子の密度が下がり、粒子が壊れやすくなる。 Regarding the slurry concentration, the mixed powder composed of melamine borate and flaky boron nitride is 10 to 50 parts by mass and preferably 20 to 40 parts by mass with respect to 100 parts by mass of the aqueous solution. When the concentration of the mixed powder is larger than 50 parts by mass, the slurry viscosity increases and spraying becomes difficult. When the concentration of the mixed powder is less than 10 parts by mass, the moisture content of the particles formed immediately before spraying is high, so that the density of the composite particles obtained by drying decreases and the particles are easily broken.
複合粒子粉末の平均粒子径は４０〜３００μｍであり、６０〜１５０μｍが好ましい。複合粒子と焼成して得られる窒化ホウ素粒子の粒径にはある程度相関があり、この相関係数は複合粒子の原料配合比、焼成条件等によって若干変化するが、概ね１である。また粒径は、放熱材料の放熱特性に影響を与える。たとえば、高熱伝導フィラーとして放熱シートに用いる際、複合粒子の粒径が３００μｍより大きいと、放熱材料表面が凹凸となりやすく、表面の接触抵抗の増加により熱伝導が低下する。４０μｍより小さいと粒子間の接点の増加に伴う接触抵抗の増加により熱伝導が低下する。 The average particle size of the composite particle powder is 40 to 300 μm, preferably 60 to 150 μm. There is a certain correlation between the particle size of the composite particles and the boron nitride particles obtained by firing, and this correlation coefficient is approximately 1 although it varies slightly depending on the raw material compounding ratio of the composite particles, firing conditions, and the like. The particle size affects the heat dissipation characteristics of the heat dissipation material. For example, when used as a high thermal conductive filler in a heat dissipation sheet, if the particle size of the composite particles is larger than 300 μm, the surface of the heat dissipation material tends to be uneven, and the thermal conductivity decreases due to an increase in contact resistance on the surface. If it is smaller than 40 μm, the heat conduction decreases due to the increase in contact resistance accompanying the increase in the contact between the particles.
上記の複合粒子を、非酸化性雰囲気下、６００〜１３００℃で焼成後、非酸化性雰囲気下、１６００〜２２００℃で焼成することによりホウ酸メラミンが窒化ホウ素となり窒化ホウ素粒子は製造される。焼成温度に関しては、特に９００〜１１００℃で焼成後、１８００〜２０００℃で焼成することが好ましい。一般的に窒化ホウ素を合成する際、原料として窒素源にメラミンや尿素などの窒素含有有機化合物を用いる場合、反応、結晶化の２段階の焼成が必要とされる。一段焼成では、窒化ホウ素の核生成が不十分となり収率が下がる、また第三成分の揮発により結晶化が抑制される等の問題が生じるためである。
焼成温度に関して一段目では、６００℃より低いと、反応が不十分となり、１３００℃より高いと、反応段階で原料や第三成分等が揮発してしまい、結晶化が進行し難くなる。２段目に関しては、１６００℃より低いと、結晶化が進行し難く、２２００℃より高いと窒化ホウ素が分解する可能性があるためである。なお、窒化ホウ素の形成はＸ線回折により確認することができる。反応が不十分である場合は、Ｘ線回折によりホウ酸メラミンに起因するピークが存在する。（段落００１０に記載の２θ＝２３．３°）
The above composite particles are fired at 600 to 1300 ° C. in a non-oxidizing atmosphere, and then fired at 1600 to 2200 ° C. in a non-oxidizing atmosphere, whereby melamine borate becomes boron nitride to produce boron nitride particles. Regarding the firing temperature, it is particularly preferable to fire at 1800 to 2000 ° C. after firing at 900 to 1100 ° C. In general, when synthesizing boron nitride, when a nitrogen-containing organic compound such as melamine or urea is used as a nitrogen source as a raw material, two-stage firing of reaction and crystallization is required. This is because the single-stage firing causes problems such as insufficient nucleation of boron nitride and a decrease in yield, and suppression of crystallization due to volatilization of the third component.
In the first stage with respect to the firing temperature, if it is lower than 600 ° C., the reaction is insufficient, and if it is higher than 1300 ° C., the raw material, the third component and the like are volatilized in the reaction stage, and crystallization is difficult to proceed. Regarding the second stage, if it is lower than 1600 ° C., crystallization hardly proceeds, and if it is higher than 2200 ° C., boron nitride may be decomposed. The formation of boron nitride can be confirmed by X-ray diffraction. If the reaction is insufficient, there is a peak due to melamine borate by X-ray diffraction. (2θ = 23.3 ° described in paragraph 0010)
窒化ホウ素の合成を非酸化性雰囲気下で行う理由は、酸化性雰囲気において、窒化ホウ素は９００℃以上の高温で、酸化され三酸化二ホウ素を形成するためである。
非酸化性雰囲気化には、窒素ガス雰囲気、アルゴンガス雰囲気等あるが、コスト面から窒素ガス雰囲気が好ましい。
The reason why boron nitride is synthesized in a non-oxidizing atmosphere is that boron nitride is oxidized at a high temperature of 900 ° C. or higher to form diboron trioxide in an oxidizing atmosphere.
The non-oxidizing atmosphere includes a nitrogen gas atmosphere, an argon gas atmosphere, etc., but a nitrogen gas atmosphere is preferable from the viewpoint of cost.
実施例１〜１６ 比較例１〜１８
ホウ酸とメラミンをヘンシェルミキサーで混合した後、恒温恒湿機中にて、温度８５℃、相対湿度８５％で６時間保持してホウ酸メラミン（ホウ酸メラミンのモル比はホウ酸：メラミン＝２：１）を調製した。調製したホウ酸メラミンと平均粒子径、黒鉛化指数が異なる鱗片状窒化ホウ素粉末を、ホウ酸メラミン１００質量部に対して鱗片状窒化ホウ素を表１及び２の割合で混合した。有機バインダーとしてポリアクリル酸アンモニウム（中央理化工業社製「ＳＡ２０３」）を用い、表１及び２の水溶液濃度に調製した。ポリアクリル酸アンモニウム水溶液１００質量部に対して、ホウ酸メラミンと窒化ホウ素粉末の混合物を表１及び２の配合で添加後、２時間混合して噴霧用スラリーを調製した。調製したスラリーを噴霧造粒機（大川原化工機社製「ＦＬ１２」）に供給し、アトマイザーの回転数１６０００ｒｐｍ、温度２００℃、スラリー供給量３ｍｌ／ｍｉｎの条件で複合粒子を作製した。得られた複合粒子粉末を窒素雰囲気下で、表１及び表２の焼成条件で焼成して、窒化ホウ素粉末を得た。窒化ホウ素粉末の平均粒子径および熱伝導率を以下に従い測定、評価した。なお、比較例１６は窒化ホウ素粉末のみ、比較例１７はホウ酸メラミンのみ、比較例１８はホウ酸メラミンを形成せずに、その原料及び窒化ホウ素粉末により造粒粒子を製造した場合である。
なお、実施例１〜１６で得られた窒化ホウ素粉末において、ホウ酸メラミンの窒化ホウ素への転化率は、9０％以上であった。
評価結果を表１及び表２に示す。
（平均粒子径）
日機装社製「マイクロトラック粒度分布測定装置ＭＴ３３００ＥＸ」を用いて、レーザー回折散乱法により測定した。なお、０．２％ヘキサメタリン酸ナトリウム水溶液２ｍｌと試料６０ｍｇを分散器（ホモジナイザー）にて分散させたスラリーを、上述測定機にて測定した。まず装置の循環水の脱泡処理を行った後、バックグランド調整を行った。次に評価サンプルを全量チャンバーにセットし、循環分散させた。測定時間を１２０秒にセットして、得られた５０％値を平均粒子径とした。
（熱伝導率測定）
窒化ホウ素造粒粒子４０体積％とシリコーン樹脂（旭化成ワッカーシリコーン社製「ＲＴ７４５’’Ｓ’’Ａ， ＲＴ７４５’’Ｓ’’Ｂ」）６０体積％を混合し、スラリーを調製した。調製したスラリーを真空脱泡した後、加硫プレス機（１５０℃、１７．６４ＭＰa）にてシートを作製した。作製したシートの熱抵抗を、ＡＳＴＭ Ｄ ５４７０に準じて測定し、測定サンプル厚みと面積から熱伝導率を算出した。
Examples 1-16 Comparative Examples 1-18
After mixing boric acid and melamine with a Henschel mixer, in a thermo-hygrostat, hold at a temperature of 85 ° C. and a relative humidity of 85% for 6 hours. Melamine borate (molar ratio of melamine borate: boric acid: melamine 2: 1) was prepared. The flaky boron nitride powder having a different average particle diameter and graphitization index from the prepared melamine borate was mixed with flaky boron nitride in a ratio of Tables 1 and 2 with respect to 100 parts by mass of melamine borate. Using ammonium polyacrylate (“SA203” manufactured by Chuo Rika Kogyo Co., Ltd.) as the organic binder, the aqueous solution concentrations shown in Tables 1 and 2 were prepared. A slurry for spraying was prepared by adding a mixture of melamine borate and boron nitride powder in the blends of Tables 1 and 2 to 100 parts by mass of an aqueous solution of ammonium polyacrylate and mixing for 2 hours. The prepared slurry was supplied to a spray granulator (“FL12” manufactured by Okawara Chemical Co., Ltd.), and composite particles were produced under the conditions of an atomizer rotation speed of 16000 rpm, a temperature of 200 ° C., and a slurry supply rate of 3 ml / min. The obtained composite particle powder was fired under a nitrogen atmosphere under the firing conditions shown in Tables 1 and 2 to obtain boron nitride powder. The average particle diameter and thermal conductivity of the boron nitride powder were measured and evaluated according to the following. Comparative Example 16 is a case where only boron nitride powder is produced, Comparative Example 17 is a case where only melamine borate is produced, and Comparative Example 18 is a case where granulated particles are produced using the raw material and boron nitride powder without forming melamine borate.
In addition, in the boron nitride powder obtained in Examples 1 to 16, the conversion rate of melamine borate to boron nitride was 90% or more.
The evaluation results are shown in Tables 1 and 2.
(Average particle size)
Measurement was performed by a laser diffraction scattering method using a “Microtrack particle size distribution analyzer MT3300EX” manufactured by Nikkiso Co., Ltd. In addition, the slurry which disperse | distributed 2 ml of 0.2% sodium hexametaphosphate aqueous solution and 60 mg of samples with the disperser (homogenizer) was measured with the above-mentioned measuring device. First, after defoaming the circulating water of the apparatus, the background was adjusted. Next, the evaluation sample was set in the whole chamber and circulated and dispersed. The measurement time was set to 120 seconds, and the obtained 50% value was taken as the average particle size.
(Thermal conductivity measurement)
40% by volume of boron nitride granulated particles and 60% by volume of a silicone resin (“RT745 ″ S ″ A, RT745 ″ S ″ B” manufactured by Asahi Kasei Wacker Silicone) were mixed to prepare a slurry. The prepared slurry was vacuum degassed, and then a sheet was produced with a vulcanizing press (150 ° C., 17.64 MPa). The thermal resistance of the produced sheet was measured according to ASTM D 5470, and the thermal conductivity was calculated from the measured sample thickness and area.
実施例と比較例の対比から、ホウ酸メラミンと鱗片状窒化ホウ素の複合粒子を用いることにより、高熱伝導率の窒化ホウ素粒子が得られた。 From the comparison between Examples and Comparative Examples, boron nitride particles with high thermal conductivity were obtained by using composite particles of melamine borate and flaky boron nitride.
本発明の窒化ホウ素粒子は、樹脂等への高熱伝導性フィラーとして利用される。また、本発明の窒化ホウ素粒子を用いた樹脂組成物は放熱材等に用いられる。
The boron nitride particles of the present invention are used as a highly thermally conductive filler for resins and the like. Moreover, the resin composition using the boron nitride particles of the present invention is used as a heat dissipation material or the like.
Claims (3)
A method for producing boron nitride particles, wherein the composite particles according to claim 1 are fired at 600 to 1300 ° C in a non-oxidizing atmosphere and then fired at 1600 to 2200 ° C in a non-oxidizing atmosphere.
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