JP7680737B2 - Thermally conductive composite particles and manufacturing method thereof - Google Patents
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本発明は、窒化ホウ素の表面に所定量のシリカを被覆することにより樹脂組成物への充填量を高め、樹脂組成物に高い熱伝導性を付与できる熱伝導性複合粒子及びその製造方法に関する。 The present invention relates to thermally conductive composite particles that can increase the loading amount in a resin composition by coating the surface of boron nitride with a specified amount of silica, thereby imparting high thermal conductivity to the resin composition, and a method for producing the same.
近年、半導体デバイスやＩＣ等の電気・電子機器の小型化や軽量化に伴い、電子部品の高密度実装化が進んでおり、電子部品からの発熱が増大する傾向にある。発生した熱が電子部品に蓄積されると耐久性に悪影響が及ぶため、発生した熱を電子部品から効率よく放出できる高熱伝導性フィラーのニーズが高まっている。
高熱伝導性フィラーとして、窒化ホウ素、窒化アルミニウム、炭化ケイ素、アルミナ、マグネシア等が挙げられる。これらの中でも、窒化ホウ素は熱伝導率が高い、絶縁性を有する、比重が小さい等の優れた特性を示すが、粒子の平板面に官能基がないため、樹脂との親和性が低く、樹脂組成物への充填量が低いという課題がある。
そのため、窒化ホウ素に他の材料を複合させることにより、樹脂との親和性を向上させて充填量を高め、熱伝導率の高い樹脂組成物を提供することを可能とする熱伝導性複合粒子が望まれている。
In recent years, with the miniaturization and weight reduction of electric and electronic devices such as semiconductor devices and ICs, electronic components are being mounted at higher densities, and there is a tendency for heat generation from electronic components to increase. If the generated heat accumulates in electronic components, it adversely affects their durability, so there is a growing need for highly thermally conductive fillers that can efficiently release the generated heat from electronic components.
Examples of high thermal conductive fillers include boron nitride, aluminum nitride, silicon carbide, alumina, magnesia, etc. Among these, boron nitride exhibits excellent properties such as high thermal conductivity, insulation, and low specific gravity, but has the problem that it has low affinity with resins and a low loading amount in resin compositions because there are no functional groups on the flat surfaces of the particles.
Therefore, there is a demand for thermally conductive composite particles that can be made by combining boron nitride with other materials to improve the affinity with resins, increase the loading amount, and provide resin compositions with high thermal conductivity.
従来、窒化ホウ素に他の材料を複合した熱伝導性複合粒子についての提案がある。例えば、窒化ホウ素にシリカが被覆した熱伝導性複合粒子（第１フィラー）の開示がある（特許文献１参照）。また、板状粒子または棒状粒子である熱伝導性フィラーと、無機粒子とを混合し、メカノケミカル処理を行って得られる熱伝導性複合粒子についての開示があり、板状粒子及び無機粒子には窒化ホウ素が包含される（特許文献２参照）。 Previously, there have been proposals for thermally conductive composite particles in which boron nitride is combined with other materials. For example, there has been a disclosure of thermally conductive composite particles (first filler) in which boron nitride is coated with silica (see Patent Document 1). There has also been a disclosure of thermally conductive composite particles obtained by mixing a thermally conductive filler, which is a plate-like or rod-like particle, with inorganic particles and subjecting the mixture to a mechanochemical treatment, in which the plate-like particles and inorganic particles include boron nitride (see Patent Document 2).
しかし、特許文献１に開示の窒化ホウ素にシリカを被覆した熱伝導性複合粒子は、樹脂組成物に充填した窒化ホウ素が加水分解して電子部品、基板あるいはヒートシンクなどを腐食するおそれがあるため、窒化ホウ素を加水分解されにくいシリカで被覆し耐湿性を改善したものであり、樹脂との親和性を向上させて樹脂組成物への充填量を高めることについては記載も示唆もない。また、メカノケミカル処理により窒化ホウ素にシリカを被覆させることについては記載も示唆もない。特許文献２に開示の熱伝導性複合粒子は、コアとなる無機粒子の表面に板状粒子または棒状粒子が結合し、機械的強度により充填された成形体の熱伝導率の異方性を低減させるもので、樹脂との親和性を向上させて樹脂組成物への充填量を高めることについては記載も示唆もない。 However, the thermally conductive composite particles of boron nitride coated with silica disclosed in Patent Document 1 are coated with silica, which is resistant to hydrolysis, to improve moisture resistance, since the boron nitride filled in the resin composition may hydrolyze and corrode electronic components, substrates, heat sinks, etc., and there is no description or suggestion of improving the affinity with resin to increase the amount of filling in the resin composition. There is also no description or suggestion of coating boron nitride with silica by mechanochemical treatment. The thermally conductive composite particles disclosed in Patent Document 2 are formed by bonding plate-shaped or rod-shaped particles to the surface of a core inorganic particle, and reduce the anisotropy of the thermal conductivity of the filled molded body due to mechanical strength, and there is no description or suggestion of improving the affinity with resin to increase the amount of filling in the resin composition.
本発明は、上記の事情に鑑みなされたもので、窒化ホウ素にシリカを被覆（複合）させることにより、樹脂との親和性を向上させて樹脂組成物への充填量を高め、樹脂組成物に高い熱伝導性を付与できる熱伝導性複合粒子及びその製造方法を提供することを課題とする。 The present invention has been made in consideration of the above circumstances, and aims to provide thermally conductive composite particles and a manufacturing method thereof that can improve the affinity with resins by coating (compounding) boron nitride with silica, thereby increasing the loading amount in a resin composition and imparting high thermal conductivity to the resin composition.
本発明者等は、上記の課題を解決するため、種々検討を重ね本発明に想到した。すなわち、本発明は、窒化ホウ素の表面にシリカが被覆されてなる熱伝導性複合粒子であって、前記シリカの被覆量は前記窒化ホウ素の質量に対し、０．５質量％未満であることを特徴とする熱伝導性複合粒子に関する。当該発明において、シリカの被覆量は窒化ホウ素の質量に対し、０．３質量％以下でもよい。 The inventors conducted various studies to solve the above problems and came up with the present invention. That is, the present invention relates to a thermally conductive composite particle in which the surface of boron nitride is coated with silica, and the amount of the silica coating is less than 0.5 mass% of the mass of the boron nitride. In this invention, the amount of silica coating may be 0.3 mass% or less of the mass of boron nitride.
また、本発明は、窒化ホウ素と沈殿法シリカ、ゲル法シリカ、乾燥シリカから選ばれる１以上のシリカを乾式法でメカノケミカル処理することを特徴とする上記の熱伝導性複合粒子の製造方法に関する。当該発明において、シリカは沈殿法シリカでもよい。 The present invention also relates to a method for producing the above-mentioned thermally conductive composite particles, characterized in that boron nitride and one or more silicas selected from precipitated silica, gel silica, and dried silica are mechanochemically treated by a dry method. In the present invention, the silica may be precipitated silica.
本発明の熱伝導性複合粒子は、樹脂との親和性が向上させられているため、樹脂組成物への充填量が高められ、樹脂組成物に高い熱伝導性を付与でき有用である。 The thermally conductive composite particles of the present invention have improved affinity with resins, so they can be loaded in a resin composition at a higher amount, and are useful in imparting high thermal conductivity to the resin composition.
本発明の熱伝導性複合粒子の製造方法は、窒化ホウ素とシリカを乾式法でメカノケミカル処理するだけで行えるので、熱伝導性複合粒子を簡易に製造でき有用である。 The method for producing thermally conductive composite particles of the present invention can be carried out simply by mechanochemically treating boron nitride and silica using a dry method, making it useful for easily producing thermally conductive composite particles.
本発明の熱伝導性複合粒子は、窒化ホウ素とシリカをメカノケミカル処理することにより製造できる。窒化ホウ素は、六方晶窒化ホウ素でも立方晶窒化ホウ素でもよいが、熱伝導性に優れる六方晶窒化ホウ素が好ましい。また、シリカは、沈殿法シリカ、ゲル法シリカ、乾燥シリカから選ばれる１以上を用いることができるが、二次粒子の凝集性が低い（凝集がほぐれ易い）という点及び易解砕性という点から沈殿法シリカを用いることが好ましい。 The thermally conductive composite particles of the present invention can be produced by mechanochemically treating boron nitride and silica. The boron nitride may be either hexagonal boron nitride or cubic boron nitride, but hexagonal boron nitride, which has excellent thermal conductivity, is preferred. The silica may be one or more selected from precipitated silica, gel silica, and dried silica, but precipitated silica is preferred because of its low agglomeration tendency of secondary particles (easy disaggregation) and easy disintegration.
メカノケミカル処理とは、対象となる原料にせん断、圧縮、摩擦、曲げ、衝撃等の機械的エネルギーを与え、原料の表面を改質する処理方法である。メカノケミカル処理の手段は特に限定されないが、ボールミル、ビーズミル、サンドミル等のメディア分散機やジェットミル粉砕機等の公知の手段を用いることができる。メカノケミカル処理の処理時間や処理条件等は、使用する手段に応じて適宜設定することができる。 Mechanochemical processing is a processing method in which mechanical energy such as shear, compression, friction, bending, and impact is applied to the target raw material to modify the surface of the raw material. There are no particular limitations on the means of mechanochemical processing, but known means such as media dispersers such as ball mills, bead mills, and sand mills, and jet mill grinders can be used. The processing time and processing conditions of the mechanochemical processing can be set appropriately depending on the means used.
また、メカノケミカル処理は、分散媒を用いる湿式法と分散媒を用いない乾式法があるが、本発明の熱伝導性複合粒子の製造は乾式法のメカノケミカル処理が好ましい。 In addition, mechanochemical treatment can be performed using a wet method that uses a dispersion medium or a dry method that does not use a dispersion medium, but the dry mechanochemical treatment method is preferred for producing the thermally conductive composite particles of the present invention.
本発明の熱伝導性複合粒子におけるシリカの被覆量は、窒化ホウ素の質量に対し、０．５質量％未満である。シリカの被覆量が０．５質量％以上になると、シリカが増加して複合粒子が嵩高くなり、充填する樹脂組成物の粘度が高められるために練込限界量が減少し、樹脂組成物に充填される窒化ホウ素も減少するからである。また、シリカは熱伝導率が低いため、シリカが増加することにより充填する樹脂組成物の熱伝導率の低下を招くからである。 The amount of silica coated in the thermally conductive composite particles of the present invention is less than 0.5% by mass relative to the mass of boron nitride. If the amount of silica coated is 0.5% by mass or more, the silica increases, the composite particles become bulky, and the viscosity of the resin composition to be filled is increased, reducing the kneading limit amount and reducing the amount of boron nitride filled in the resin composition. In addition, because silica has low thermal conductivity, an increase in silica leads to a decrease in the thermal conductivity of the resin composition to be filled.
また、本発明の熱伝導性複合粒子におけるシリカの被覆量は、窒化ホウ素の質量に対し、０．３質量％以下であることが好ましく、０．３質量％がより好ましい。シリカの被覆量が０．３質量％以下になると、練込限界量が増加し、樹脂組成物に充填される窒化ホウ素も増加するからである。 In addition, the amount of silica coating in the thermally conductive composite particles of the present invention is preferably 0.3 mass% or less, more preferably 0.3 mass%, relative to the mass of boron nitride. If the amount of silica coating is 0.3 mass% or less, the kneading limit increases, and the amount of boron nitride filled into the resin composition also increases.
本発明の熱伝導性複合粒子は、樹脂組成物、特に基板、半導体パッケージ又は工業用樹脂材料に充填し、熱伝導性フィラーとして使用することができる。ここで、工業用樹脂材料とは、耐食、耐薬品性、加工性（特に切断、曲げ、溶接）等が要求される樹脂材料で例えば工業用プレートを挙げられる。樹脂組成物に用いられる樹脂は特に限定されないが、エポキシ樹脂、シリコーン樹脂、メラミン樹脂、ユリア樹脂、フェノール樹脂、不飽和ポリエステル、フッ素樹脂、ポリイミド、ポリアミドイミド、ポリエーテルイミド、ナイロン等のポリアミド、ポリブチレンテレフタレート、ポリエチレンテレフタレート等のポリエステル、ポリベンゾイミダゾール、アラミド樹脂、ポリフェニレンスルフィド、全芳香族ポリエステル、液晶ポリマー、ポリスルホン、ポリエーテルスルホン、ポリカーボネート、マレイミド変性樹脂、ＡＢＳ樹脂、アクリロニトリル－アクリルゴム・スチレン樹脂、アクリロニトリル・エチレン・プロピレン・ジエンゴム－スチレン樹脂、ポリエチレン、ポリプロピレン、ポリ塩化ビニル、ポリスチレン等の汎用樹脂等を例示できる。 The thermally conductive composite particles of the present invention can be filled into a resin composition, particularly a substrate, a semiconductor package, or an industrial resin material, and used as a thermally conductive filler. Here, the industrial resin material is a resin material that requires corrosion resistance, chemical resistance, and processability (particularly cutting, bending, and welding), and examples thereof include industrial plates. The resin used in the resin composition is not particularly limited, and examples thereof include epoxy resin, silicone resin, melamine resin, urea resin, phenol resin, unsaturated polyester, fluororesin, polyimide, polyamideimide, polyetherimide, nylon and other polyamides, polybutylene terephthalate, polyethylene terephthalate and other polyesters, polybenzimidazole, aramid resin, polyphenylene sulfide, wholly aromatic polyester, liquid crystal polymer, polysulfone, polyethersulfone, polycarbonate, maleimide-modified resin, ABS resin, acrylonitrile-acrylic rubber-styrene resin, acrylonitrile-ethylene-propylene-diene rubber-styrene resin, polyethylene, polypropylene, polyvinyl chloride, polystyrene, and other general-purpose resins.
次いで、本発明を実施例を挙げて説明するが、本発明は以下の実施例に限定されるものではない。 Next, the present invention will be described with reference to examples, but the present invention is not limited to the following examples.
〔実施例１〕（シリカの被覆量が０．３質量％の複合粒子）
窒化ホウ素（グレード名：HS、エアブラウン株式会社製）300gと沈殿法シリカ（グレード名：Nipsil LP、東ソー株式会社製）0.9gを高速混合造粒機により高速撹拌させること（メカノケミカル処理、乾式法）で図１に示す窒化ホウ素の質量に対してシリカの被覆量が０．３質量％の複合粒子を得た。高速混合造粒機の容積は2Lで、撹拌速度5000rpm、混合時間は20分である。図１に示す複合粒子のＳＥＭ写真は、得られた複合粒子をカーボンテープの上に張り付け、走査型電子顕微鏡（装置名：日本電子株式会社製、JSM-7500FA）を用いて複合粒子の表面及び形状を観察したものである。以下の図２～図４も同様である。
[Example 1] (Composite particles with silica coating amount of 0.3 mass %)
300 g of boron nitride (grade name: HS, manufactured by Air Brown Co., Ltd.) and 0.9 g of precipitated silica (grade name: Nipsil LP, manufactured by Tosoh Corporation) were mixed at high speed (mechanochemical treatment, dry method) in a high-speed mixer granulator to obtain composite particles with a silica coating amount of 0.3% by mass relative to the mass of boron nitride shown in Figure 1. The volume of the high-speed mixer granulator was 2 L, the mixing speed was 5000 rpm, and the mixing time was 20 minutes. The SEM photograph of the composite particles shown in Figure 1 was obtained by attaching the obtained composite particles to carbon tape and observing the surface and shape of the composite particles using a scanning electron microscope (device name: JSM-7500FA, manufactured by JEOL Ltd.). The same applies to Figures 2 to 4 below.
〔比較例１〕（未処理の窒化ホウ素）
窒化ホウ素（グレード名：HS、エアブラウン株式会社）をそのまま使用した。図２に示すように、窒化ホウ素の表面は平滑である。
Comparative Example 1 (Untreated Boron Nitride)
Boron nitride (grade name: HS, Air Brown Co., Ltd.) was used as is. As shown in Figure 2, the surface of boron nitride is smooth.
〔比較例２〕（メカノケミカル処理された窒化ホウ素）
沈殿法シリカを添加しない以外は、実施例１と同様の方法で窒化ホウ素をメカノケミカル処理した。図３に示す窒化ホウ素は、表面が改質されている。
Comparative Example 2 (Mechanochemically Treated Boron Nitride)
Boron nitride was mechanochemically treated in the same manner as in Example 1, except that no precipitated silica was added. The boron nitride shown in Figure 3 has a surface modified.
〔比較例３〕（シリカの被覆量が０．５質量％の複合粒子）
窒化ホウ素（グレード名：HS、エアブラウン株式会社）300gと沈殿法シリカ（グレード名：Nipsil LP、東ソー株式会社製）1.5gを高速混合造粒機により高速撹拌させること（メカノケミカル処理、乾式法）で図４に示す窒化ホウ素の質量に対してシリカの被覆量が０．５質量％の複合粒子を得た。高速混合造粒機の容積は2Lで、撹拌速度5000rpm、混合時間は20 分である。
[Comparative Example 3] (Composite particles with silica coating amount of 0.5% by mass)
300 g of boron nitride (grade name: HS, Air Brown Co., Ltd.) and 1.5 g of precipitated silica (grade name: Nipsil LP, Tosoh Corporation) were mixed at high speed in a high-speed mixer granulator (mechanochemical treatment, dry method) to obtain composite particles with a silica coating amount of 0.5 mass% relative to the mass of boron nitride, as shown in Figure 4. The volume of the high-speed mixer granulator was 2 L, the mixing speed was 5000 rpm, and the mixing time was 20 minutes.
上記の実施例１及び比較例１～３の各試料（複合粒子又は窒化ホウ素）について、下記の測定を行った。 The following measurements were carried out for each sample (composite particles or boron nitride) in Example 1 and Comparative Examples 1 to 3 above.
１．水分量
試料の吸湿性を評価する。吸湿性が高いと樹脂組成物の特性に悪影響を与える可能性がある。
試料5gを水分計（装置名：株式会社エー・アンド・デイ製、MX-50）に載せ、130℃強熱時の重量減少率を測定し、水分量とした。
２．比表面積
メカノケミカル処理によって、試料が破砕／磨砕されて微細化が進行していないかを評価する。微細化が進行すると、熱伝導率の低下や水分量の増加（耐吸湿性の低下）を招く可能性がある。
全自動比表面積測定装置（装置名：株式会社マウンテック製、Macsorb（登録商標） HM model-1200）を使用して試料のＢＥＴ比表面積を測定した。測定前に150℃で30分の真空加熱排気による前処理を行い、液体窒素温度近傍（77K）でBET流動法（1点法）により測定した。
３．中心粒子径
メカノケミカル処理によって、試料が破壊されて微細化していないかを評価する。熱伝導性フィラーの粒子径が大きくなると熱伝導パスが長く太くなり熱伝導率が向上し、逆に粒子径が小さくなると熱伝導率が低下することはよく知られている。本発明においても、複合粒子又は窒化ホウ素が破壊されて中心粒子径が小さくなると、熱伝導率の低下を招く可能性がある。
0.2%ヘキサメタりん酸ナトリウム水溶液に試料を分散させ、粒度分布測定装置（マイクロトラック・ベル株式会社製、MT3000）を用いて粒度分布を測定し、D50の値を読み取った。
４．吸液量
樹脂への練り込み易さを評価する。樹脂へ練り込み易くなる（多量に充填できる）ことによって、樹脂組成物の熱伝導率の向上が期待できる。
吸液量測定は、流動パラフィンを用いてＪＩＳ５１０１－１３－２の煮あまに油法を参考とした。測定手順は次のとおりである。
（１）試料2ｇを秤量し、ガラス製の測定板の上に置いた。
（２）流動パラフィンをスポイトから１回につき4～5滴ずつ徐々に加え、パレットナイフで流動パラフィンに試料を練り込んだ。
（３）上記（２）の操作を繰り返し行い、流動パラフィンと試料の塊ができるところまで滴下を続けた。
（４）以後、流動パラフィンを1滴ずつ滴下し、完全に混練するようにして繰り返し、ペーストが柔らかな硬さになったところを終点とした。
（５）終点迄に要した流動パラフィンの重量を100倍し、吸液量（単位g/100g）とした。
５．分散液試験（pH・電気伝導度）
メカノケミカル処理によって、窒化ホウ素の分解に伴う酸化ホウ素（B2O3）の発生等、不純物の含有量が増加していないかを評価する。例えば、B2O3の発生量が多いと、最終製品（樹脂組成物）の特性に悪影響を与える可能性がある。
純水1Lに試料10ｇを入れて撹拌して懸濁液を得た。ハンディpH・電気伝導率計（装置名：東亜ディーケーケー株式会社製、WM-32EP）を使用して、pH及び電気伝導度（率）を測定した。
６．酸化ホウ素含有量
メカノケミカル処理によって、窒化ホウ素の分解に伴う酸化ホウ素（B2O3）の発生が進んでいないかを評価する。B2O3の発生量が多いと、最終製品（樹脂組成物）の特性に悪影響を与える可能性がある。また、電気伝導度やpH値に影響を与える。
純水1Lに試料10ｇを入れて撹拌して懸濁液を固液分離した後、ICP発光分光分析装置（装置名：サーモフィッシャーサイエンティフィック株式会社製、iCAP7200Duo）を使用してホウ素濃度を測定し、その測定値から酸化ホウ素含有量を算出した。
７．熱伝導率
（１）205mLの紙コップにエポキシ樹脂（三井化学株式会社製、エポミックR140P）40gを入れ、練込限界量になるまで試料を徐々に配合し、自転・公転ミキサー（株式会社シンキー製ARE-310）で混合する作業を繰り返した。練込限界量まで配合・混合後、2-エチル-4-メチルイミダゾール（和光純薬工業株式会社製）を0.8g加えて十分に混合・脱泡し、120℃で2時間加熱硬化した。
練込限界量における体積充填率は次の式により導出した。
試料の体積充填率（vol%）=（試料の体積（cm3）/（試料の体積（cm3）+エポキシ樹脂の体積（cm3）））×100 （式１）
試料の体積（cm3）= 試料重量（g）/試料の密度（g/cm3） （式２）
エポキシ樹脂の体積（cm3）= エポキシ樹脂の重量（g）/エポキシ樹脂の密度（g/cm3） （式３）
比較例１、比較例２の試料の密度は窒化ホウ素の密度を使用した。
実施例１、比較例３は（式４）～（式６）を用いて試料の密度を算出した。
試料の密度（g/cm3）= 窒化ホウ素の密度（g/cm3）×（試料中の窒化ホウ素の割合（質量%）/ 100）+ シリカの密度（g/cm3）×（試料中のシリカの割合（質量%）/100） （式４）
試料中の窒化ホウ素の割合（質量%）=（窒化ホウ素の処理質量（g）/（窒化ホウ素の処理質量（g）+ シリカの処理質量（g）））×100 （式５）
試料中のシリカの割合（質量%）=（シリカの処理質量（g）/（窒化ホウ素の処理質量（g）+ シリカの処理質量（g）））×100 （式６）
窒化ホウ素の密度：2.27g/cm3、エポキシ樹脂の密度：1.16g/cm3、沈殿法シリカの密度：2.2g/cm3
（２）硬化した樹脂組成物を研磨し、直径5cm、厚さ2cmの熱伝導率測定用試験試料を作製した。
（３）熱伝導率測定用試験試料を25℃の恒温槽で2時間以上保持した後、迅速熱伝導計（京都電子工業株式会社製、QTM-500）を使用して樹脂組成物の熱伝導率を測定した。
1. Moisture content: Evaluate the moisture absorption of the sample. High moisture absorption may adversely affect the properties of the resin composition.
Five grams of the sample was placed on a moisture meter (device name: MX-50, manufactured by A&D Co., Ltd.) and the weight loss rate upon ignition at 130°C was measured, which was taken as the moisture content.
2. Specific surface area: Evaluate whether the sample has been crushed/ground and reduced in size by mechanochemical treatment. If the sample is reduced in size, it may lead to a decrease in thermal conductivity and an increase in moisture content (decreased moisture absorption resistance).
The BET specific surface area of the sample was measured using a fully automatic specific surface area measuring device (Macsorb (registered trademark) HM model-1200, manufactured by Mountec Co., Ltd.). Before the measurement, the sample was pretreated by vacuum heating and evacuation at 150°C for 30 minutes, and the measurement was performed by the BET flow method (single point method) at a temperature close to the liquid nitrogen temperature (77K).
3. Median particle size Evaluate whether the sample is broken down and pulverized by the mechanochemical treatment. It is well known that as the particle size of the thermally conductive filler increases, the thermal conduction path becomes longer and thicker, improving the thermal conductivity, and conversely, as the particle size decreases, the thermal conductivity decreases. In the present invention, if the composite particles or boron nitride are broken down and the median particle size decreases, this may lead to a decrease in thermal conductivity.
The sample was dispersed in a 0.2% aqueous solution of sodium hexametaphosphate, and the particle size distribution was measured using a particle size distribution measuring device (MT3000, manufactured by Microtrack Bell Co., Ltd.) to read the D50 value.
4. Liquid Absorption Amount Ease of kneading into resin is evaluated. By making it easier to knead into resin (able to fill a large amount), it is expected that the thermal conductivity of the resin composition will improve.
The liquid absorption was measured using liquid paraffin according to the boiled linseed oil method of JIS 5101-13-2. The measurement procedure was as follows.
(1) 2 g of sample was weighed and placed on a glass measuring plate.
(2) Liquid paraffin was gradually added from the dropper, 4 to 5 drops at a time, and the sample was kneaded into the liquid paraffin with a palette knife.
(3) The above procedure (2) was repeated, and the dropping was continued until a mass of liquid paraffin and sample was formed.
(4) After that, liquid paraffin was added drop by drop and the process was repeated until the paste became soft and hard.
(5) The weight of liquid paraffin required up to the end point was multiplied by 100 to obtain the amount of liquid absorbed (unit: g/100 g).
5. Dispersion test (pH, electrical conductivity)
We evaluate whether the mechanochemical treatment increases the content of impurities, such as the generation of boron oxide (B 2 O 3 ) due to the decomposition of boron nitride. For example, if a large amount of B 2 O 3 is generated, it may have a negative effect on the properties of the final product (resin composition).
10 g of the sample was added to 1 L of pure water and stirred to obtain a suspension. The pH and electrical conductivity (rate) were measured using a handy pH/electrical conductivity meter (device name: WM-32EP, manufactured by DKK-TOA Corporation).
6. Boron oxide content This is evaluated to see if the generation of boron oxide ( B2O3 ) caused by the decomposition of boron nitride by mechanochemical treatment is progressing. If the amount of B2O3 generated is large, it may have a negative effect on the properties of the final product (resin composition). It also affects the electrical conductivity and pH value.
10 g of the sample was added to 1 L of pure water and stirred to separate the suspension into solid and liquid. The boron concentration was then measured using an ICP optical emission spectrometer (instrument name: iCAP7200Duo, manufactured by Thermo Fisher Scientific K.K.), and the boron oxide content was calculated from the measured value.
7. Thermal conductivity (1) 40g of epoxy resin (Mitsui Chemicals, Epomic R140P) was placed in a 205mL paper cup, and the sample was gradually mixed until the kneading limit was reached, and the mixing process was repeated using a centrifugal mixer (Thinky ARE-310). After mixing and mixing to the kneading limit, 0.8g of 2-ethyl-4-methylimidazole (Wako Pure Chemical Industries, Ltd.) was added, thoroughly mixed and degassed, and then heated and cured at 120℃ for 2 hours.
The volume filling rate at the kneading limit was calculated using the following formula.
Volume filling rate of sample (vol%)=(volume of sample (cm 3 )/(volume of sample (cm 3 )+volume of epoxy resin (cm 3 )))×100 (Equation 1)
Sample volume (cm 3 ) = Sample weight (g) / Sample density (g/cm 3 ) (Equation 2)
Volume of epoxy resin (cm 3 ) = Weight of epoxy resin (g) / Density of epoxy resin (g/cm 3 ) (Equation 3)
The density of the samples of Comparative Example 1 and Comparative Example 2 was the density of boron nitride.
In Example 1 and Comparative Example 3, the density of the sample was calculated using (Equation 4) to (Equation 6).
Density of sample (g/cm 3 ) = density of boron nitride (g/cm 3 ) × (percentage of boron nitride in the sample (mass%)/100) + density of silica (g/cm 3 ) × (percentage of silica in the sample (mass%)/100) (Equation 4)
Percentage of boron nitride in sample (mass%) = (treated mass of boron nitride (g) / (treated mass of boron nitride (g) + treated mass of silica (g))) x 100 (Equation 5)
Percentage of silica in sample (mass%) = (mass of silica (g) / (mass of boron nitride (g) + mass of silica (g))) x 100 (Equation 6)
Density of boron nitride: 2.27g/cm 3 , density of epoxy resin: 1.16g/cm 3 , density of precipitated silica: 2.2g/cm 3
(2) The cured resin composition was polished to prepare a test sample for measuring thermal conductivity having a diameter of 5 cm and a thickness of 2 cm.
(3) Thermal Conductivity Measurement The test sample was kept in a thermostatic chamber at 25° C. for 2 hours or more, and then the thermal conductivity of the resin composition was measured using a rapid thermal conductivity meter (QTM-500, manufactured by Kyoto Electronics Manufacturing Co., Ltd.).
実施例１及び比較例１～３の測定結果を表１に示した。 The measurement results for Example 1 and Comparative Examples 1 to 3 are shown in Table 1.
表１から実施例１、比較例１、比較例２及び比較例３について、以下の解析ができる。
実施例１：樹脂組成物に練込限界量（樹脂組成物に充填できる最大量）を充填した場合、樹脂組成物の熱伝導率は各比較例と比べて最も高く、窒化ホウ素の有する高度な熱伝導性能を樹脂組成物に十分に付与することができる。また、実施例１と比較例２のそれぞれの練込限界量に差違がない、すなわち樹脂組成物に充填される窒化ホウ素の量に差違がないにも拘わらず、実施例１の練込限界量を充填した樹脂組成物の熱伝導率が比較例２のそれより高いのは、実施例１は効率の良い熱伝導パスが形成されるからである。その理由については次のように考えられる。図５の左図に示すように、樹脂との混練時に窒化ホウ素の表面の微量の微少シリカがスペーサーの役割をすることにより、ランダムな方向に向いた窒化ホウ素は、「窒化ホウ素の端面－窒化ホウ素の平面」の接触点の形成が促進され、効率の良い三次元的な熱伝導パスのネットワークが形成されることにより熱伝導率が高められるからと考えられる。この機序から、窒化ホウ素にごく僅かでもシリカが被覆されている限り、比較例２の樹脂組成物の熱伝導率を凌駕する。したがって、本発明の熱伝導性複合粒子におけるシリカの被覆量の下限を設定することは特に馴染まないが、例えば窒化ホウ素の質量に対し、シリカの被覆量が０．０１質量％でも０．０５質量％でも比較例２の樹脂組成物の熱伝導率を凌駕する。
比較例１：吸液量が実施例１や他の比較例より高いことから、樹脂との親和性が最も低く練込限界量が低いので、練込限界量を充填しても熱伝導率の高い樹脂組成物を得られないことが分かる。
比較例２：メカノケミカル処理で窒化ホウ素の表面が改質されているため、樹脂との親和性が高められ、比較例１より吸液量が低く、樹脂組成物への練込限界量は比較例１より高い。しかし、比較例２は比較例１に比べて練込限界量が高いにも拘わらず、両者の樹脂組成物の熱伝導率にほとんど差違がないのは、以下の理由によると考えられる。比較例２は、図５の右図に示すように、シリカのスペーサーが存在しないため、メカノケミカル処理された窒化ホウ素を樹脂に充填した場合、実施例１のような三次元的な熱伝導パスのネットワークが形成されないばかりか、窒化ホウ素－樹脂－窒化ホウ素という接触（熱伝導パス）が実施例１より多くなり、樹脂は熱伝導率が低いために窒化ホウ素－樹脂のその境界面の熱抵抗が大きくなる（熱伝導率が悪くなる）からと考えられる。他方、未処理の窒化ホウ素の比較例１は、比較例２よりも中心粒子径が大きい（比較例１：26.6 μm、比較例２：18.8 μm）ため、比較例２と比べて長く太い熱伝導パスを形成できるため、練込限界量が低いにも拘わらず熱伝導率が高くなると考えられる。
比較例３：樹脂組成物に練込限界量を充填した場合の熱伝導率は、被覆されるシリカの増加で樹脂組成物の粘度が高まり練込限界量が減少すること及び熱伝導率が低いシリカの増加で樹脂組成物の熱伝導率が低下することにより、比較例１、比較例２と比べて若干高いものの、実施例１に比べて低い。また、電気伝導度及びB2O3含有量が実施例１より高く、B2O3等の不純物の含有量が実施例１より増加し、樹脂組成物の特性に悪影響を与える可能性がある。したがって、シリカの被覆量が０．５質量％の比較例３は本発明の熱伝導性複合粒子の境界点であると考えられる。
From Table 1, the following analysis can be made for Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3.
Example 1: When the resin composition is filled with the kneading limit amount (the maximum amount that can be filled in the resin composition), the thermal conductivity of the resin composition is the highest compared to each comparative example, and the high thermal conductivity performance of boron nitride can be fully imparted to the resin composition. In addition, even though there is no difference in the kneading limit amount between Example 1 and Comparative Example 2, that is, there is no difference in the amount of boron nitride filled in the resin composition, the thermal conductivity of the resin composition filled with the kneading limit amount of Example 1 is higher than that of Comparative Example 2 because an efficient heat conduction path is formed in Example 1. The reason for this is thought to be as follows. As shown in the left diagram of FIG. 5, a small amount of fine silica on the surface of boron nitride acts as a spacer when kneaded with resin, and the boron nitride oriented in a random direction promotes the formation of contact points between the end face of boron nitride and the plane of boron nitride, and an efficient three-dimensional heat conduction path network is formed, which is thought to increase the thermal conductivity. From this mechanism, as long as the boron nitride is coated with even a small amount of silica, the thermal conductivity exceeds that of the resin composition of Comparative Example 2. Therefore, although it is not particularly convenient to set a lower limit for the amount of silica coated in the thermally conductive composite particles of the present invention, for example, the thermal conductivity exceeds that of the resin composition of Comparative Example 2 even if the amount of silica coated is 0.01 mass% or 0.05 mass% relative to the mass of boron nitride.
Comparative Example 1: Since the amount of liquid absorption is higher than that of Example 1 and other comparative examples, it is understood that the affinity with the resin is the lowest and the kneading limit amount is low, so that even if the kneading limit amount is filled, a resin composition with high thermal conductivity cannot be obtained.
Comparative Example 2: The surface of boron nitride is modified by mechanochemical treatment, so that its affinity with resin is increased, and the amount of liquid absorption is lower than that of Comparative Example 1, and the kneading limit amount into the resin composition is higher than that of Comparative Example 1. However, although Comparative Example 2 has a higher kneading limit amount than Comparative Example 1, there is almost no difference in the thermal conductivity of the two resin compositions, which is believed to be due to the following reasons. In Comparative Example 2, as shown in the right diagram of FIG. 5, there is no silica spacer, so when mechanochemically treated boron nitride is filled into the resin, not only is a three-dimensional network of thermal conduction paths like that in Example 1 not formed, but the contact (thermal conduction path) of boron nitride-resin-boron nitride is more than that in Example 1, and the thermal resistance of the interface between boron nitride and resin increases (thermal conductivity becomes poor). This is believed to be because of this. On the other hand, the untreated boron nitride of Comparative Example 1 has a larger central particle size than that of Comparative Example 2 (Comparative Example 1: 26.6 μm, Comparative Example 2: 18.8 μm), and therefore can form longer and thicker heat conduction paths than that of Comparative Example 2. This is thought to result in a higher thermal conductivity despite the lower kneading limit amount.
Comparative Example 3: The thermal conductivity when the resin composition is filled with the kneading limit amount is slightly higher than those of Comparative Examples 1 and 2, but lower than that of Example 1, because the viscosity of the resin composition increases with the increase in the silica to be coated, which reduces the kneading limit amount, and the thermal conductivity of the resin composition decreases with the increase in silica with low thermal conductivity. In addition, the electrical conductivity and B2O3 content are higher than those of Example 1, and the content of impurities such as B2O3 is higher than that of Example 1, which may adversely affect the properties of the resin composition. Therefore, Comparative Example 3, in which the silica coating amount is 0.5 mass%, is considered to be the boundary point of the thermally conductive composite particles of the present invention.
本発明の熱伝導性複合粒子は、樹脂に充填することにより樹脂に高い熱伝導性を付与できるので、電子部品等の放熱が必要な樹脂成形体に好適である。 The thermally conductive composite particles of the present invention can impart high thermal conductivity to resins by filling them with the particles, making them suitable for use in resin molded products that require heat dissipation, such as electronic components.
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