JP5111821B2 - Alumina particles, production method thereof, and resin composition using alumina particles - Google Patents
Alumina particles, production method thereof, and resin composition using alumina particles Download PDFInfo
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本発明は、高熱伝導性フィラーとして用いられるアルミナ粒子およびその製造方法、アルミナ粒子を用いた樹脂組成物、特に封止用樹脂組成物や放熱シート用途に用いられる樹脂組成物に関する。 The present invention relates to alumina particles used as a high thermal conductive filler, a method for producing the same, a resin composition using the alumina particles, particularly a sealing resin composition and a resin composition used for a heat radiation sheet.
最近、エレクトロニクスの進展に伴い、パワーデバイス等電子機器内において発熱する部品が多く使用されてきている。電子回路を制御するに当り、これらの発熱部品からの熱を放散させて系全体を冷却することが重要となってきた。 Recently, with the progress of electronics, many components that generate heat have been used in electronic devices such as power devices. In controlling an electronic circuit, it has become important to dissipate heat from these heat generating components to cool the entire system.
半導体素子を樹脂中に封止して用いる場合には、素子の発熱を、封止樹脂を介して外部へ放散させることとなり、封止樹脂の熱伝導率を向上させる方法として、無機フィラーの材質が検討されている。 When a semiconductor element is encapsulated in a resin, the heat generated from the element is dissipated to the outside through the encapsulating resin, and as a method for improving the thermal conductivity of the encapsulating resin, an inorganic filler material is used. Is being considered.
放熱シートとは、発熱部品と放熱フィンや金属板との間に設置され、圧着により隙間のないように密着し、発熱部品から発生した熱を放熱フィン等に伝えて、系全体の抜熱をさせるシートのことであり、従来の熱伝導性接着剤等に比べて取り扱いの容易さ等により最近普及してきた部材である。放熱シートの場合にも、熱伝導性フィラーによる熱伝導率特性向上が検討されている。 A heat dissipation sheet is installed between a heat-generating component and a heat-dissipating fin or metal plate. It is a sheet to be used, and is a member that has recently become popular due to its ease of handling and the like compared to conventional heat conductive adhesives and the like. Also in the case of a heat-dissipating sheet, improvement of thermal conductivity characteristics using a thermally conductive filler has been studied.
一般に、封止樹脂や放熱シートに代表される高熱伝導性樹脂成形体は、高熱伝導性の無機フィラーと樹脂との組成物で構成されている。無機フィラーとしては、安価なシリカや水酸化アルミニウムや酸化アルミニウム（以下、アルミナ）、高熱伝導率の炭化珪素や窒化硼素、窒化アルミニウムといった材料が用いられている。封止樹脂用の樹脂としては、エポキシ樹脂が一般的である。また、放熱シート用の樹脂としてはシリコーン樹脂が一般的であるが、シリコーン樹脂に含まれるシロキサンによる接点不良の問題を解決すべく、アクリル系ゴム等の適用も検討されてきている。 Generally, a highly heat conductive resin molded body represented by a sealing resin or a heat dissipation sheet is composed of a composition of a highly heat conductive inorganic filler and a resin. As the inorganic filler, inexpensive materials such as silica, aluminum hydroxide, aluminum oxide (hereinafter referred to as alumina), high thermal conductivity silicon carbide, boron nitride, and aluminum nitride are used. An epoxy resin is generally used as the resin for the sealing resin. In addition, a silicone resin is generally used as a resin for the heat dissipation sheet, but application of acrylic rubber or the like has been studied in order to solve the problem of contact failure due to siloxane contained in the silicone resin.
放熱シートや封止材料の開発においては、安価で高熱伝導率を有する無機フィラーを用いて、できるだけ熱伝導率を向上させるための研究開発が進められてきており、中でも、アルミナの形状や配合についての研究が多々なされている。 In the development of heat-dissipating sheets and sealing materials, research and development for improving thermal conductivity as much as possible using inorganic fillers that are inexpensive and have high thermal conductivity have been promoted. A lot of research has been done.
例えば、樹脂に加えるアルミナの充填率を上げることで高熱伝導率化を目指す方法が多く研究されており、フィラーの充填・分散を容易にするものとして、下記特許文献１に記載されているように角を落とした丸味状アルミナを用いるものや、下記特許文献２に記載されているように球状アルミナを用いるもの等、流動性を良くすることにより充填率を上げるため、アルミナの形状に関する研究が行なわれた。 For example, many methods for increasing the thermal conductivity by increasing the filling rate of alumina to be added to the resin have been studied. As described in Patent Document 1 below, the method for facilitating filling and dispersion of the filler has been studied. In order to increase the filling rate by improving fluidity, such as those using rounded alumina with rounded corners, and those using spherical alumina as described in Patent Document 2 below, research on the shape of alumina has been conducted It was.
また下記特許文献３には、熱伝導フィラー（実施例として炭化珪素）を樹脂に充填するに当り、大きな粒子とその間隙に入る小さな粒子を組合せることで、熱伝導フィラーの充填率を上げて熱伝導を向上させた放熱シートが得られることが記載されている。フィラーの充填率を上げるべく、大小の粒径の異なる粒子を配合することを開示したものである。また、その考えをさらに進めて、大きな粒子の間隙に入る小さな粒子の間隙にさらに微細粒子を加えるといった研究もなされている。（下記特許文献４参照）
しかし、微細粒子を添加すると、粒子の隙間をさらに粒子で埋めることができ、フィラーの充填率がさらに向上するため、熱伝導率を向上させることが可能となる、という思想は、特許文献１〜３には記載がない。また特許文献４では、微細粒子を添加することが記載されているが、実施例にあるようにエポキシ樹脂に関するもので、シリコーン樹脂を用いたものではなかった。
Further, in Patent Document 3 below, when filling a resin with a heat conductive filler (silicon carbide as an example), the filling rate of the heat conductive filler is increased by combining large particles and small particles entering the gaps. It is described that a heat radiating sheet with improved heat conduction can be obtained. In order to increase the filling rate of the filler, it is disclosed that particles having different sizes are mixed. In addition, studies have been made to further advance the idea and to add finer particles to the gaps between the small particles that enter the gaps between the large particles. (See Patent Document 4 below)
However, when fine particles are added, the gap between the particles can be further filled with particles, and the filling rate of the filler is further improved, so that the thermal conductivity can be improved. There is no description in 3. In addition, Patent Document 4 describes that fine particles are added. However, as described in Examples, it relates to an epoxy resin and does not use a silicone resin.
また、下記特許文献５には、大径粒子よりなる粉体（粉体Ａ）と小径粒子よりなる粉体（粉体Ｂ）を高温火炎中に導入し粉体Ａ表面に粉体Bを溶融・付着させることにより樹脂との接着性向上のため必要な表面改質と球状化を同一工程で行なう方法が記載されている。 In Patent Document 5 below, powder (powder A) consisting of large particles and powder (powder B) consisting of small particles are introduced into a high-temperature flame, and the powder B is melted on the surface of the powder A. A method is described in which the surface modification and spheroidization required for improving the adhesion to the resin by adhesion are performed in the same process.
しかし、この特許文献５に記載された表面改質方法では、溶融・付着する小径の粉体Ｂは溶融状態で球状となった後、大径の粉体Ａの表面に付着する際に、半球状の突起もしくは、曲面付着（大径粒子表面を覆う）となる結果、樹脂内における粒子同士の接触点が点接触になり易く、熱伝導向上効果が十分でないという問題点があった。 However, in the surface modification method described in Patent Document 5, the small diameter powder B to be melted and adhered becomes spherical in the molten state, and then adheres to the surface of the large diameter powder A to form a hemisphere. As a result of stick-like projections or curved surface adhesion (covering the surface of large-diameter particles), there is a problem that the contact point between the particles in the resin tends to be point contact, and the effect of improving heat conduction is not sufficient.
また、下記特許文献６には、母粒子に子粒子を一体化もしくは混じり合った複合粒子を機械的（圧縮と剪断）に形成させる方法が記載されている。 Patent Document 6 below describes a method of mechanically (compressing and shearing) forming composite particles in which child particles are integrated or mixed with mother particles.
この特許文献６に記載された複合粒子の製造方法によれば、大径粒子の隙間に小径粒子を均一に分散させる状態は作れるが、セラミックスを物理的に付着させることは困難であり、付着より先に大径粒子の破壊が起こると考えられる。 According to the method for producing composite particles described in Patent Document 6, it is possible to create a state in which small-diameter particles are uniformly dispersed in the gaps between large-diameter particles, but it is difficult to physically attach ceramics. It is thought that the large particle breaks first.
また、下記特許文献７には、ボールミル等の混合の際の衝撃・摩擦・せん断等のエネルギーにより母粒子にシリカを含む子粒子（酸化チタン−シリカ複合粒子）を結合させる方法が記載されている。 Patent Document 7 listed below describes a method of binding child particles containing silica (titanium oxide-silica composite particles) to mother particles by energy such as impact, friction, and shear during mixing in a ball mill or the like. .
しかし、この特許文献７の方法では、母粒子と子粒子を結合させるバインダとして機能しているシリカ成分が存在しないアルミナ粒子同士が結合した複合粒子を作ることはできなかった。 However, in the method of Patent Document 7, composite particles in which alumina particles that do not have a silica component functioning as a binder for bonding mother particles and child particles do not exist cannot be formed.
また、下記特許文献８には、電融アルミナとアルミナ水和物（水酸化アルミニウム等）を造粒後、1000〜1600℃で焼結する丸み状アルミナ粒子の製造方法が記載されている。 Patent Document 8 below describes a method for producing rounded alumina particles in which fused alumina and alumina hydrate (such as aluminum hydroxide) are granulated and then sintered at 1000 to 1600 ° C.
しかし、この特許文献８の方法による熱処理後の粗大粒は２次凝集粒となるため、粗大粒同士の付着も起こっており、これを塊砕して単一粒子に変形するので、中間体としての大径粒子と小径粒子の結合した複合粒子は製造できなかった。
微細粒子は凝集しやすいために二次粒子での挙動を示すことが多い。そのため、うまく微細粒子の凝集を解いて分散させないと、粒子の間隙に微細粒子を入れることは困難であり、熱伝導率の向上は見込めない。 Since fine particles tend to aggregate, they often exhibit behavior in secondary particles. For this reason, unless fine particles are agglomerated and dispersed well, it is difficult to put fine particles into the gaps between the particles, and improvement in thermal conductivity cannot be expected.
さらに、うまく分散ができたとしても、低硬度のシリコーン樹脂を用いた場合には、微細粒子によるシリコーン樹脂の硬化阻害が起こるといった問題を生じることがある。原因は明確ではないが、シリコーン樹脂の硬化反応を起こす触媒に微細粒子が何らかの影響を及ぼし、硬化反応が起こらなくなると考えられている。 Furthermore, even if the dispersion is successful, there is a problem that when a low-hardness silicone resin is used, the curing of the silicone resin by fine particles may be inhibited. Although the cause is not clear, it is considered that the fine particles have some influence on the catalyst that causes the curing reaction of the silicone resin, and the curing reaction does not occur.
本発明は、微細粒子を用いて高熱伝導化させることと、微細粒子の影響によって樹脂が硬化阻害を起こすことを防止することの２つの課題を同時に解決させようというものである。 The present invention is intended to simultaneously solve the two problems of increasing the thermal conductivity using fine particles and preventing the resin from inhibiting the curing due to the influence of the fine particles.
本発明は、前述の課題を解決するために鋭意検討の結果なされたものであり、その要旨とするところは特許請求の範囲に記載した通りの下記内容である。
（１）平均粒径5μｍ以上の大径アルミナ粒子の表面に平均粒径4μｍ以下の微細アルミナ粒子を焼結反応により付着させて突起部を形成したことを特徴とするフィラー用アルミナ粒子。
（２）前記微細アルミナ粒子が不定形であることを特徴とする（１）に記載のフィラー用アルミナ粒子。
（３）前記大径アルミナ粒子の粒径が微細アルミナの5〜300倍であることを特徴とする（１）または（２）に記載のフィラー用アルミナ粒子。
（４）大径アルミナ粒子の表面積の少なくとも10％の面積に、該微細アルミナ粒子が付着した突起部が形成されていることを特徴とする請求項１乃至請求項３のいずれか一項に記載のフィラー用アルミナ粒子。
（５）（１）乃至（４）のいずれか一項に記載のアルミナ粒子をフィラーとして用いることを特徴とする樹脂組成物。
（６）前記樹脂組成物が封止用に用いられることを特徴とする（５）に記載の樹脂組成物。
（７）前記樹脂組成物が放熱用に用いられることを特徴とする（５）に記載の樹脂組成物。
（８） 平均粒径5μｍ以上の大径アルミナ粒子と平均粒径4μｍ以下の微細アルミナ粒子を混合し、その後に1150〜1500℃で熱処理を施し、焼結反応により大径アルミナ粒子の表面に小径アルミナ粒子を付着させて突起部を形成することを特徴とするフィラー用アルミナ粒子の製造方法。
（９）前記微細アルミナ粒子が不定形であることを特徴とする（８）に記載のフィラー用アルミナ粒子の製造方法。
The present invention has been made as a result of intensive studies in order to solve the above-described problems, and the gist of the present invention is the following contents as described in the claims.
(1) Alumina particles for filler, wherein protrusions are formed by attaching fine alumina particles having an average particle size of 4 μm or less to the surface of large alumina particles having an average particle size of 5 μm or more by a sintering reaction .
( 2) The alumina particles for filler as described in (1), wherein the fine alumina particles are indefinite.
(3) The alumina particles for filler according to (1) or (2), wherein the large-diameter alumina particles have a particle size of 5 to 300 times that of fine alumina.
(4) Projections to which the fine alumina particles are attached are formed in an area of at least 10% of the surface area of the large-diameter alumina particles. Alumina particles for filler .
(5) A resin composition using the alumina particles according to any one of (1) to ( 4) as a filler.
(6) The resin composition according to (5), wherein the resin composition is used for sealing.
(7) The resin composition as described in (5), wherein the resin composition is used for heat dissipation.
(8) Mix large alumina particles with an average particle size of 5 μm or more and fine alumina particles with an average particle size of 4 μm or less, then heat-treat at 1150-1500 ° C. A method for producing alumina particles for filler , characterized in that the protrusions are formed by adhering alumina particles.
( 9) The method for producing alumina particles for filler as described in (8), wherein the fine alumina particles are amorphous.
本発明のアルミナ粒子は、大径アルミナ粒子に微細アルミナ粒子が付着しており、熱伝導の経路となる粒子間の接触箇所が予め形成されている。そのため、微細粒子を分散させて大きな粒子と接触させる場合と比べ接触箇所即ち熱伝導の経路が多くなることから、本発明のアルミナ粒子を用いると熱伝導率が向上する。また、微細粒子をそのまま添加した場合に硬化阻害を起こしてしまうシリコーン樹脂等と混合しても硬化阻害を起こすことなく使用できる。 In the alumina particles of the present invention, fine alumina particles are attached to large-diameter alumina particles, and contact portions between the particles serving as heat conduction paths are formed in advance. Therefore, compared with the case where fine particles are dispersed and brought into contact with large particles, the number of contact points, that is, the heat conduction path is increased. Therefore, when the alumina particles of the present invention are used, the thermal conductivity is improved. Moreover, even if it mixes with the silicone resin etc. which raise | generates hardening inhibition when adding a fine particle as it is, it can be used without raise | generating hardening inhibition.
さらに、大径アルミナ粒子として球状アルミナ粒子を用いた場合には、球状粒子の特徴である流動性を殆ど損なうことなく高充填化でき、熱伝導率向上に寄与する。 Further, when spherical alumina particles are used as the large-diameter alumina particles, high packing can be achieved without substantially impairing the fluidity that is characteristic of the spherical particles, which contributes to improvement in thermal conductivity.
また、このアルミナ配合粒子をフィラー、もしくはその一部として用いた樹脂組成物を高熱伝導の封止樹脂とすることが可能である。 Further, a resin composition using the alumina-mixed particles as a filler or a part thereof can be used as a high thermal conductive sealing resin.
また、このアルミナ配合粒子をフィラー、もしくはその一部として用いた樹脂組成物を使い、放熱シートや放熱グリースといった高熱伝導の放熱材料を作製することも可能となる。 Further, it is possible to produce a heat radiation material with high thermal conductivity such as a heat radiation sheet or heat radiation grease by using a resin composition using the alumina-mixed particles as a filler or a part thereof.
本発明者らは、微細粒子を添加して充填率を上げ、熱伝導率を向上させることを鋭意検討し、予め大径粒子の表面に微細粒子を付着させて接触箇所増加を確実にしておくことで、熱伝導率が向上することを見出した。特に、大径粒子が半球状の突起もしくは、曲面付着（大径粒子表面を覆う）の場合には粒子同士の接触が点接触になり易いが、付着させた微細粒子により、粒子同士の接触点が確実に増加するため、その効果が明確に現れる。なお、この場合に、微細粒子が不定形（非球状）であると、その接触点が球状微細粒子の場合よりも格段に増えることから、その効果がさらに明確となる。 The inventors of the present invention have intensively studied to increase the filling rate by adding fine particles and improve the thermal conductivity, and ensure that the number of contact points is increased by attaching fine particles to the surface of the large particle in advance. It was found that the thermal conductivity is improved. In particular, when the large particle is a hemispherical protrusion or curved surface adhesion (covers the surface of the large particle), the contact between the particles tends to be point contact, but the contact point between the particles due to the adhered fine particles Will definitely increase, so the effect is clear. In this case, if the fine particles are indefinite (non-spherical), the contact point increases remarkably as compared with the case of the spherical fine particles, and thus the effect is further clarified.
この不定形の微細粒子は、微細粒子を溶融球状化させないで、微細粒子の元の形状を維持した粒子を用いることが好ましい。ここに、不定形粒子とは、粒子の平均最大径Ｌ１に対する平均最小径Ｌ２の比Ｌ２/Ｌ１の値が０．７未満の粒子をいい、球状粒子とは、粒子の平均最大径Ｌ１に対する平均最小径Ｌ２の比Ｌ２/Ｌ１の値が０．７以上の粒子をいう。 As the irregular fine particles, it is preferable to use particles that maintain the original shape of the fine particles without causing the fine particles to melt and spheroidize. Here, the irregular particle means a particle having a ratio L2 / L1 of the average minimum diameter L2 to the average maximum diameter L1 of the particle of less than 0.7, and the spherical particle means an average of the average maximum diameter L1 of the particle. A particle having a ratio L2 / L1 of the minimum diameter L2 of 0.7 or more.
さらに、本発明の微細粒子を付着させた大径アルミナ粒子を用いることで、シリコーン樹脂と混合しても硬化阻害を起こすことがなくなった。 Furthermore, by using the large-diameter alumina particles to which the fine particles of the present invention are attached, curing inhibition does not occur even when mixed with a silicone resin.
微細粒子を大径粒子に付着させる方法として、熱処理を施して焼結反応により付着させる方法を開発したが、接着剤等を利用して、微細粒子を付着させても構わない。例えば、表面改質剤であるシランカップリング剤を大径粒子表面に付着させておき、その後、微細粒子と混合させることで、微細粒子を付着させた大径アルミナ粒子を得ることが可能となる。 As a method of attaching fine particles to large-diameter particles, a method of applying heat treatment and attaching them by a sintering reaction has been developed, but fine particles may be attached using an adhesive or the like. For example, it is possible to obtain large-diameter alumina particles to which fine particles are adhered by adhering a silane coupling agent, which is a surface modifier, to the surfaces of large-diameter particles and then mixing with the fine particles. .
なお、大径粒子が球状等流動性に優れた形状を有する際に、大径粒子に突起を形成する本発明の粒子では流動性が劣化する傾向が生じるが、微細粒子の径が大径粒子に対して十分小さければ、流動性を著しく損なうことはなく、高充填化により熱伝導率を増加させることの妨げになることはなかった。 In addition, when the large-diameter particles have a shape having excellent fluidity such as a spherical shape, fluidity tends to deteriorate in the particles of the present invention that form protrusions on the large-diameter particles. If it is sufficiently small, the fluidity is not significantly impaired, and the increase in thermal conductivity is not hindered by the high filling.
微細粒子を大径粒子に付着させるのに、球状粒子を製造するのと同じ火炎中にて大径粒子と微細粒子を混合させる方法が特許文献５（特開平2004-262674号公報）に開示されている。これは、球状粒子の表面改質を施すために、大径球状粒子の表面に火炎中で溶融させた微細粒子を付着させるもので、微細粒子が他の成分であれば、大径粒子の表層部に他の元素を存在させるという表面改質を施すものである。高粘性の樹脂に対してフィラーとして用いる場合に、高流動性により充填率を高めるのが課題としている。 In order to attach fine particles to large particles, a method of mixing large particles and fine particles in the same flame as producing spherical particles is disclosed in Patent Document 5 (Japanese Patent Laid-Open No. 2004-262674). ing. This is to attach fine particles melted in a flame to the surface of the large-diameter spherical particles in order to modify the surface of the spherical particles. If the fine particles are other components, the surface layer of the large-diameter particles The surface is modified so that other elements are present in the part. When using it as a filler with respect to highly viscous resin, it is making the subject to raise a filling rate by high fluidity | liquidity.
微細粒子が同じ成分であっても表面処理の効果が得られると文献には記載があるが、流動性を高めるという課題の技術に対して、本願のような突起を有するのは文献の課題に対して反対の行為となる。即ち、本願はもともと流動性の高い球状粒子表面に、流動性を多少犠牲にしてでも熱伝導率を高めるために熱伝導パスを形成するものであり、樹脂との接着性を高めるという文献とは思想が異なるものである。 Although there is a description in the literature that the effect of surface treatment can be obtained even if the fine particles are the same component, it is a problem of the literature to have a protrusion like this application in contrast to the technique of the problem of improving fluidity. It is the opposite action. That is, the present application originally forms a heat conduction path on the surface of spherical particles with high fluidity in order to increase thermal conductivity even at the expense of fluidity. The idea is different.
また、文献では火炎中で微細粒子を溶融・付着させると記載されており、微細粒子を火炎中で溶融した状態で大径粒子表面に付着させており、微細粒子の溶融は起こらない焼結反応を用いている本発明とは態様が異なる。文献の場合には、微細粒子が溶融していることから球状化している状態で大径粒子に付着しており、本願の技術思想の一つである「熱伝導率を高めるために、接触点を増加させるのに効果的な不定形（非球状）微細粒子を大径粒子表面に（焼結反応で）付着させることは、文献の方法ではでき得ないものである。 In addition, it is described in the literature that fine particles are melted and adhered in a flame, and the fine particles are adhered to the surface of a large particle in the melted state in a flame, so that the fine particles do not melt. This embodiment is different from the present invention that uses. In the case of the literature, since the fine particles are melted and adhered to the large-diameter particles in a spheroidized state, one of the technical ideas of the present application is “contact points to increase thermal conductivity. It is not possible to attach amorphous (non-spherical) fine particles effective for increasing the amount to the surface of large particles (by a sintering reaction) by the literature method.
この特許文献５に記載された表面改質方法では、溶融・付着する小径の粉体Ｂは球状となるため、大径の粉体Ａの表面において半球状の突起もしくは、曲面付着（大径粒子表面を覆う）となる結果、樹脂内における粒子同士の接触点が点接触になり易く、熱伝導向上効果が十分でないという問題点があった。 In the surface modification method described in Patent Document 5, since the small-sized powder B to be melted and adhered becomes spherical, hemispherical protrusions or curved surface adhesion (large-sized particles) on the surface of the large-diameter powder A As a result of covering the surface, there is a problem that the contact point between the particles in the resin tends to be point contact, and the effect of improving heat conduction is not sufficient.
大径粒子に付着させる微細粒子の粒径について説明する。微細粒子の粒径が大き過ぎると、大径粒子表面に大きな突起ができることになるので、粒子の流動性が悪化し、高充填化が困難となり、熱伝導率も向上しなくなる。さらに、本発明のように熱処理を施して粒子を付着させる場合には、微細粒子の粒径が大きくなると、焼結反応を起こすための温度を高くせざるを得ず、大径粒子同士の焼結反応が開始する温度になってしまう。大径粒子同士が焼結してしまうと、粒子の流動性が著しく悪化する。種々の実験の結果、粒子の流動性が悪化せずに熱伝導率向上に寄与するための微細粒子の粒径の好ましい範囲は4.0μｍ以下とした。 The particle size of the fine particles attached to the large particle will be described. If the particle size of the fine particles is too large, large protrusions are formed on the surface of the large particle, so that the fluidity of the particles deteriorates, it becomes difficult to achieve high packing, and the thermal conductivity does not improve. Furthermore, when the particles are adhered by heat treatment as in the present invention, if the particle size of the fine particles is increased, the temperature for causing the sintering reaction must be increased, and the large particles are sintered together. It becomes the temperature at which the freezing reaction starts. If the large-diameter particles are sintered together, the fluidity of the particles is significantly deteriorated. As a result of various experiments, the preferable range of the particle size of the fine particles for contributing to the improvement of the thermal conductivity without deteriorating the fluidity of the particles was set to 4.0 μm or less.
また、微細粒子の粒径の下限は定めなくても良いが、0.1μｍ超とすることがより好ましい。これは、微細粒子の粒径が0.1μｍより小さくなると、微細粒子が凝集しやすくなり、数μｍ〜数十μｍの凝集粒子として大径粒子に付着することがあり、粒子の流動性の低下が起こることがあるためである。 Further, the lower limit of the particle size of the fine particles may not be determined, but is more preferably more than 0.1 μm. This is because when the particle size of the fine particles is smaller than 0.1 μm, the fine particles are likely to aggregate, and may adhere to the large-sized particles as aggregated particles of several μm to several tens of μm. Because it may happen.
微細粒子の粒径が0.1μｍ超4.0μｍ以下の範囲であると、流動性を担保したまま熱伝導率の向上に寄与し、また凝集粒子による悪影響も防ぐことが可能となることから、より好適な範囲となる。 If the particle size of the fine particles is in the range of more than 0.1μm and less than 4.0μm, it contributes to the improvement of thermal conductivity while ensuring fluidity, and it is possible to prevent adverse effects due to the agglomerated particles. Range.
大径粒子の粒径について説明する。大径粒子は小さすぎると、微細粒子との焼結反応の際に、大径粒子同士も焼結反応を開始してしまい、その結果、粒子の流動性が著しく悪化する。そのため、大径粒子の粒径は5.0μｍ以上とした。10μｍ以上であるとさらに好ましい。 The particle size of the large particle will be described. If the large-diameter particles are too small, the large-diameter particles also start the sintering reaction during the sintering reaction with the fine particles, and as a result, the fluidity of the particles is significantly deteriorated. Therefore, the particle size of the large particle is set to 5.0 μm or more. More preferably, it is 10 μm or more.
大径粒子の粒径の上限については、巨大な粒子であっても、微細粒子による接触箇所増加による熱伝導率向上の効果は得られることから、上限は規定しない。発明者らが用いた最大径の球状アルミナ粒子は100μｍであり、上限を100μｍと例示することができる。 With respect to the upper limit of the particle size of the large-diameter particle, even if it is a large particle, the effect of improving the thermal conductivity due to the increase of the contact location by the fine particle can be obtained, so the upper limit is not specified. The spherical alumina particles having the maximum diameter used by the inventors are 100 μm, and the upper limit can be exemplified as 100 μm.
大径粒子の粒径ｄ１と微細粒子の粒径ｄ２の比d1/d2が5.0未満であれば、大径粒子表面に付着している微細粒子が大きな突起となり、粒子の流動性が著しく低下する。d1/d2が300を超えると、大径粒子表面に付着している微細粒子による突起が小さくなり過ぎ、流動性に悪影響を及ぼすことは殆どないが、他の粒子と接触する機会が減ることから、熱伝導率の向上は小さくなる。従って、微細粒子に対する大径粒子の粒径の比率は、５〜３００倍の範囲であることが好ましく、さらに、１０〜２００倍の範囲であると、粒子の流動性を殆ど阻害することなく熱伝導率向上の効果が顕著に見られるため、より好ましい範囲となる。 If the ratio d1 / d2 of the particle size d1 of the large particle and the particle size d2 of the fine particle is less than 5.0, the fine particle adhering to the surface of the large particle becomes a large protrusion, and the fluidity of the particle is remarkably lowered. . When d1 / d2 exceeds 300, the protrusions due to the fine particles adhering to the surface of the large-diameter particles are too small, and the fluidity is hardly adversely affected, but the chance of contact with other particles is reduced. The improvement in thermal conductivity is small. Therefore, the ratio of the particle size of the large particle to the fine particle is preferably in the range of 5 to 300 times, and more preferably in the range of 10 to 200 times, the heat of the particles is hardly inhibited. Since the effect of improving the conductivity is noticeable, it becomes a more preferable range.
本発明者らは大径粒子の表面に付着している微細粒子の量についても熱伝導率向上と粒子の流動性に大きな影響を持つことを見出した。付着している微細粒子の量については、大径粒子表面にどれくらい微細粒子が付着している部分があるかという規定を採用した。即ち、走査型電子顕微鏡等により粒子の写真を撮り、画像処理により大径粒子の表面積Sと大径粒子上で微細粒子がなく大径粒子表面が観察される部分の面積S2を求め、両者の差S-S2から微細粒子の存在している部分の面積S1を算出し、大径粒子の表面積で割った値S1/Sを微細粒子が付着している部分の面積比として求める方法である。大径粒子の表面が見えない部分は必ずしも微細粒子が大径粒子に付着しているわけではなく、微細粒子同士が付着して大径粒子表面を覆っておる場合もある。その場合を含めて、本発明では大径粒子が微細粒子に覆われている部分を微細粒子が付着しているものとして定義する。従って、微細粒子が大径粒子の同じ箇所に複数個付いた場合でも一個付いた場合と同様に取り扱う。微細粒子が複数個付く際に、層状に付着したものが複数層になっても同様に取り扱う。 The present inventors have found that the amount of fine particles adhering to the surface of large-sized particles has a great influence on the improvement of thermal conductivity and the fluidity of the particles. For the amount of fine particles adhering, the rule of how much fine particles are attached to the surface of the large particle was adopted. That is, a photograph of the particles is taken with a scanning electron microscope or the like, and the surface area S of the large particle and the area S2 where the surface of the large particle is observed without any fine particles are obtained by image processing. In this method, the area S1 of the portion where the fine particles are present is calculated from the difference S-S2, and the value S1 / S divided by the surface area of the large particles is obtained as the area ratio of the portion where the fine particles are attached. In the portion where the surface of the large particle is not visible, the fine particles are not necessarily attached to the large particle, and the fine particles may adhere to cover the surface of the large particle. Including the case, in the present invention, the portion where the large particle is covered with the fine particle is defined as the fine particle adhering. Therefore, even when a plurality of fine particles are attached to the same part of the large-diameter particle, they are handled in the same manner as when one is attached. When a plurality of fine particles are attached, the same thing is handled even if the particles adhering to the layer form a plurality of layers.
少なくとも10個の粒子についてこのような観察・算出を行ない、平均値を用いることで、大径粒子の表面のうち微細粒子が付着している部分の面積比をより精度良く定めることができる。微細粒子の付着している部分が大径粒子の表面積の10%未満の場合には、微細粒子による接触箇所が少ないために、熱伝導率の向上が小さい。そこで、大径粒子の表面積の10％以上の部分で付着していることが望ましい。 By performing such observation / calculation on at least 10 particles and using the average value, the area ratio of the portion of the surface of the large particle to which the fine particles are attached can be determined with higher accuracy. When the portion where the fine particles are attached is less than 10% of the surface area of the large-diameter particles, the number of contact points by the fine particles is small, so the improvement in thermal conductivity is small. Therefore, it is desirable that the particles adhere to a portion of 10% or more of the surface area of the large particle.
但し、微細粒子の粒径が小さい場合などは微細粒子が凝集体を形成し、かなり多数の微細粒子同士が凝集したまま付着してしまい、突起が大きくなり過ぎることがあり、その場合には流動性が悪化して高充填ができなくなる。この場合には、微細粒子の粒子径を限定することで、凝集粒子を除外することが必要となる。 However, when the particle size of the fine particles is small, the fine particles form aggregates, and a large number of fine particles adhere to each other in an aggregated state, and the protrusions may become too large. The quality deteriorates and high filling becomes impossible. In this case, it is necessary to exclude the aggregated particles by limiting the particle diameter of the fine particles.
次に、本発明のアルミナ粒子を適用した用途について説明する。本発明のアルミナ粒子をフィラーもしくはその一部として用い、シリコーン樹脂やエポキシ樹脂、ポリアミド樹脂やアクリル樹脂等と混合することで、高熱伝導性の樹脂組成物を得ることができる。 Next, the use to which the alumina particles of the present invention are applied will be described. A resin composition having high thermal conductivity can be obtained by using the alumina particles of the present invention as a filler or a part thereof and mixing with a silicone resin, an epoxy resin, a polyamide resin, an acrylic resin, or the like.
この樹脂組成物をチップホルダに流し込み、樹脂を硬化させると封止材となる。また、シート成形を施した後に樹脂を硬化させると、放熱シートや放熱グリースといった放熱材料とすることができる。シリコーン樹脂の場合には、高熱伝導率を有しかつ柔軟性のある放熱シートとすることができる。 When this resin composition is poured into a chip holder and the resin is cured, a sealing material is obtained. Further, when the resin is cured after the sheet molding, a heat dissipation material such as a heat dissipation sheet or heat dissipation grease can be obtained. In the case of a silicone resin, a heat dissipation sheet having high thermal conductivity and flexibility can be obtained.
次に、本発明のアルミナ粒子を製造する方法について説明する。1)大径アルミナ粒子と微細アルミナ粒子を混合し、2)混合粉を、大径アルミナ粒子の表面で微細粒子との焼結反応が起こる温度で熱処理を行なう。以上の２つの工程を具備することで本発明のアルミナ粒子を得ることができる。 Next, a method for producing the alumina particles of the present invention will be described. 1) Mix large-diameter alumina particles and fine alumina particles, and 2) heat the mixed powder at a temperature at which a sintering reaction with the fine particles occurs on the surface of the large-diameter alumina particles. By including the above two steps, the alumina particles of the present invention can be obtained.
ここで、焼結温度について説明する。一般に、アルミナは1400〜1600℃で焼結する材料であると知られているが、焼結開始温度は粒子の粒径や形状により大きく変化する。種々の実験の結果、粒径が小さいほど焼結開始温度が低く、粒径が大きいと焼結開始温度が高くなることを見出した。粒径による焼結開始温度差を利用することで、大径粒子同士は焼結せずに、微細粒子が大径粒子表面にて焼結反応を起こす温度条件を見出すことができた。 Here, the sintering temperature will be described. In general, alumina is known to be a material sintered at 1400 to 1600 ° C., but the sintering start temperature varies greatly depending on the particle size and shape of the particles. As a result of various experiments, it was found that the smaller the particle size, the lower the sintering start temperature, and the larger the particle size, the higher the sintering start temperature. By utilizing the difference in the sintering start temperature depending on the particle size, it was possible to find a temperature condition in which fine particles cause a sintering reaction on the surface of the large particle without sintering the large particles.
即ち、平均粒径1μｍ以下の微細粒子の焼結開始温度は1150℃程度、平均粒径1〜4μｍ程度の粒子の焼結開始温度は1200℃程度、平均粒径5〜9μｍでは1300℃程度、平均粒径が10μｍ以上であると焼結開始温度は1400℃を超え、平均粒径が20μｍ以上であると1500℃近くになるとの結果を得た。 That is, the sintering start temperature of fine particles having an average particle size of 1 μm or less is about 1150 ° C., the sintering start temperature of particles having an average particle size of about 1 to 4 μm is about 1200 ° C., and the average particle size of 5 to 9 μm is about 1300 ° C. When the average particle size was 10 μm or more, the sintering start temperature exceeded 1400 ° C., and when the average particle size was 20 μm or more, the result was close to 1500 ° C.
熱処理温度が1150℃未満の場合には、微細粒子の焼結開始温度以下となるため、微細粒子と大径粒子の焼結が十分に起こらないため、本発明のようなアルミナ粒子を得ることは難しい。微細粒子にかかわる焼結が不十分となり、アルミナ粒子を樹脂と混合する際に微細粒子は大径粒子に付着せずに単独で存在することになり、シリコーン樹脂の硬化阻害を引き起こし、封止できない、シート化できない、という問題を起こしやすくなる。そのため、熱処理温度の下限は1150℃が好ましい。 When the heat treatment temperature is less than 1150 ° C., the sintering temperature of the fine particles is below the sintering start temperature, so that the sintering of the fine particles and the large-diameter particles does not occur sufficiently. difficult. Sintering involving fine particles becomes insufficient, and when alumina particles are mixed with resin, the fine particles do not adhere to the large-diameter particles and exist alone, which inhibits curing of the silicone resin and cannot be sealed. It becomes easy to cause the problem that it cannot be made into a sheet. Therefore, the lower limit of the heat treatment temperature is preferably 1150 ° C.
一方、微細粒子の粒径が1〜4μｍの場合には、焼結反応を開始するのに1200℃程度の温度が必要となるが、熱処理温度が1200℃以上であれば全ての粒径の微細粒子が焼結反応を十分に起こし得ることから、下限は1200℃であることがより好ましい。 On the other hand, when the particle size of the fine particles is 1 to 4 μm, a temperature of about 1200 ° C. is required to start the sintering reaction. The lower limit is more preferably 1200 ° C., since the particles can sufficiently cause a sintering reaction.
熱処理温度が1500℃を超えると20μｍ以上の大径粒子同士でも十分な焼結反応を起こすようになり、粒子の流動性に悪影響を及ぼしやすくなるため、1500℃以下の熱処理が好ましい。 When the heat treatment temperature exceeds 1500 ° C., large particles having a diameter of 20 μm or more will cause a sufficient sintering reaction, and the fluidity of the particles tends to be adversely affected. Therefore, heat treatment at 1500 ° C. or less is preferable.
熱処理時間は、例えば0.5〜48時間という値が例示できる。 An example of the heat treatment time is 0.5 to 48 hours.
以下、本発明を実施例により詳細に説明する。 Hereinafter, the present invention will be described in detail with reference to examples.
表１に示す粒径の大径アルミナ球状粒子と微細アルミナ不定形粒子を、体積比で90：10となるように混合機にて1時間混合した後、1400℃×1時間大気中で熱処理を施した。 After mixing the large-diameter spherical alumina particles and fine alumina amorphous particles shown in Table 1 for 1 hour in a mixer so that the volume ratio is 90:10, heat treatment is performed in air at 1400 ° C for 1 hour. gave.
得られたアルミナ粒子を走査型電子顕微鏡で確認し、微細粒子がアルミナ粒子の表面に付着していることが確認できた。画像処理により大径粒子部の表面積Sと微細粒子のないエリアの面積S2を求め微細粒子の存在する部分の面積S1と大径粒子表面積Sとの比を粒子数10個の平均で求めた。 The obtained alumina particles were confirmed with a scanning electron microscope, and it was confirmed that the fine particles adhered to the surface of the alumina particles. The surface area S of the large particle part and the area S2 of the area without the fine particles were obtained by image processing, and the ratio of the area S1 of the part where the fine particles are present to the large particle surface area S was obtained as an average of 10 particles.
このアルミナ粒子とシリコーン樹脂CY52-276（東レダウコーニング製）をアルミナ充填率が75vol%となるように秤量し、30分混合した後、得られたスラリーの粘度をレオメーター（レオロジカ製）により測定した。 The alumina particles and silicone resin CY52-276 (manufactured by Toray Dow Corning) are weighed so that the alumina filling rate is 75 vol%, mixed for 30 minutes, and then the viscosity of the resulting slurry is measured with a rheometer (manufactured by Rheology). did.
スラリーをシート形状の型に流し込み、樹脂硬化条件（70℃×30分）で硬化させ、放熱シートを得た。 The slurry was poured into a sheet-shaped mold and cured under resin curing conditions (70 ° C. × 30 minutes) to obtain a heat dissipation sheet.
得られた放熱シートからφ50×2.5mmtの試料を切り抜き、熱流計法熱伝導率測定装置（栄弘精機）を用いて、熱流計法で測定して熱伝導率を測定した。
（Gr.1：大径粒子径）
Gr.1の発明例・比較例は、微細アルミナ粒子径を1.0μｍとして大径アルミナ粒子径を4〜100μｍまで変化させ、1400℃の熱処理で付着させた粒子を用いて、樹脂と混合した際のスラリー粘度とシート化して測定したシート熱伝導率を評価したものである。
A φ50 × 2.5 mmt sample was cut out from the obtained heat-dissipating sheet, and the thermal conductivity was measured by a heat flow meter method using a heat flow meter method thermal conductivity measuring device (Eihiro Seiki).
(Gr.1: Large particle size)
Gr.1 invention example / comparative example, when the fine alumina particle diameter is 1.0 μm, the large alumina particle diameter is changed from 4 to 100 μm, and the particles adhered by heat treatment at 1400 ° C. are mixed with the resin. The sheet thermal conductivity measured by making the slurry viscosity and the sheet is evaluated.
大径粒子径が小さくなると、スラリー粘度が増加し、シート熱伝導率も低下していき、大径粒子径が5μｍ未満となると、スラリー粘度が著しく増加し、シート熱伝導率が低くなった。 As the large particle diameter decreased, the slurry viscosity increased and the sheet thermal conductivity decreased, and when the large particle diameter was less than 5 μm, the slurry viscosity increased significantly and the sheet thermal conductivity decreased.
大径粒子が5μｍ以上の場合に、シート熱伝導率が高熱伝導放熱シートとなる5.0W/mK以上となり、 大径粒子径が10μｍを超えると、シート熱伝導率が5.5W/mKを超え、さらに好適な範囲となった。
（Gr.2：微細粒子径）
Gr.2の発明例・比較例は、大径アルミナ粒子径を35μｍとして微細アルミナ粒子径を0.05〜5μｍまで変化させた場合のものである。
When the large particle size is 5μm or more, the sheet thermal conductivity is 5.0W / mK or more, which becomes a high thermal conduction heat dissipation sheet. When the large particle size exceeds 10μm, the sheet thermal conductivity exceeds 5.5W / mK, Furthermore, it became a suitable range.
(Gr.2: Fine particle size)
The invention examples and comparative examples of Gr.2 are cases in which the large alumina particle diameter is 35 μm and the fine alumina particle diameter is changed from 0.05 to 5 μm.
微細粒子が大きくなると熱伝導率が向上し、5.0W/mK以上となる範囲があるが、スラリー粘度の増加も起こり、付着部の面積分率も低下することが分かった。微細粒子径が4μｍを超えると、スラリー粘度が著しく増加し、シート熱伝導率が5.0W/mKより小さくなり、好適な範囲と言えなくなった。 As the fine particles become larger, the thermal conductivity is improved and there is a range of 5.0 W / mK or more, but it has been found that the slurry viscosity increases and the area fraction of the adhered portion also decreases. When the fine particle diameter exceeds 4 μm, the slurry viscosity is remarkably increased and the sheet thermal conductivity becomes smaller than 5.0 W / mK, which is not a suitable range.
微細粒子径が0.1μｍ超であれば上記結果に従うが、微細粒子径が0.1μｍ以下の場合には微細粒子の凝集体としての挙動が見られた。微細粒子が0.01μｍの場合、電顕で確認したところ、0.01μｍの微細粒子ではなく1.0μｍ程度の凝集体として存在し、1.0μｍの微細粒子が付着した場合と同様な付着状況が観察された。また、スラリー粘度やシート熱伝導率も1.0μｍの微細粒子の場合に類似した値を示していた。一方、微細粒子径が0.05μｍの場合、4μｍ程度の凝集体の存在が確認でき、スラリー粘度が悪化し、シート熱伝導率も5.0W/mKであった。凝集体は必ずしも全てが4μｍ程度ではないため、付着している部分の面積比やスラリー粘度悪化も微細粒子が4μｍの場合程は悪くなっていなかった。
（Gr.3：粒径比）
Gr.3の発明例・比較例は、大径アルミナ粒子径d1を10、35μｍとして微細アルミナ粒子径d2を変えて、大径と微細の粒径比d1/d2を4〜350と変化させた場合のものである。
When the fine particle diameter exceeds 0.1 μm, the above result is followed. When the fine particle diameter is 0.1 μm or less, the behavior as an aggregate of fine particles was observed. When the fine particles were 0.01 μm, it was confirmed by an electron microscope that they were present as aggregates of about 1.0 μm instead of 0.01 μm fine particles, and the same adhesion situation as when 1.0 μm fine particles adhered was observed. . The slurry viscosity and sheet thermal conductivity were similar to those in the case of 1.0 μm fine particles. On the other hand, when the fine particle diameter was 0.05 μm, the presence of aggregates of about 4 μm could be confirmed, the slurry viscosity deteriorated, and the sheet thermal conductivity was 5.0 W / mK. Since all the aggregates are not necessarily about 4 μm, the area ratio of the adhering portion and the deterioration of the slurry viscosity were not as bad as when the fine particles were 4 μm.
(Gr.3: Particle size ratio)
In the invention example and comparative example of Gr.3, the large alumina particle diameter d1 was changed to 10 and 35 μm, and the fine alumina particle diameter d2 was changed, and the large / fine particle diameter ratio d1 / d2 was changed to 4 to 350. Is the case.
粒径比が5〜300の間だと、スラリー粘度は高くなることがなく、シート熱伝導率も5.5〜6.0W/mKと高熱伝導シートが得られた。 When the particle size ratio was between 5 and 300, the slurry viscosity did not increase and the sheet thermal conductivity was 5.5 to 6.0 W / mK, and a high thermal conductive sheet was obtained.
粒径比が5未満だと、スラリー粘度が著しく増加し、熱伝導率の向上が少なく5.0W/mKに留まった。粒径比が300超だと、スラリー粘度の増加はないものの熱伝導率の向上が少なく5.1W/mKに留まった。
（Gr.4：面積比）
Gr.4の発明例は、平均粒径35μｍの大径アルミナ粒子と平均粒径1.0μｍの微細アルミナ粒子を、突起部の面積比を変えるべく体積比を変えて、1400℃の熱処理で付着させる微細粒子の量を変化させたものである。大径粒子／小径粒子の体積比は、発明例14で98/2、発明例15で95/5、発明例16で93/7、発明例3は前述の通り90/10である。
When the particle size ratio is less than 5, the slurry viscosity is remarkably increased, and the thermal conductivity is not improved so much and remains at 5.0 W / mK. When the particle size ratio was more than 300, the slurry viscosity did not increase, but the thermal conductivity was little improved and remained at 5.1 W / mK.
(Gr.4: Area ratio)
In the invention example of Gr.4, large-diameter alumina particles having an average particle diameter of 35 μm and fine alumina particles having an average particle diameter of 1.0 μm are attached by heat treatment at 1400 ° C. while changing the volume ratio to change the area ratio of the protrusions. The amount of fine particles is changed. The volume ratio of large particles / small particles is 98/2 in Invention Example 14, 95/5 in Invention Example 15, 93/7 in Invention Example 16, and 90/10 in Invention Example 3 as described above.
大径粒子の表面積Sと微細粒子の存在する部分の面積S1の面積比S1/Sが10％未満であると、熱伝導率の向上が少なく5.1W/mKに留まった。一方、S1/Sが10％を超えると、5.5〜6.2W/mKと高熱伝導シートを得ることができた。 When the area ratio S1 / S of the surface area S of the large-diameter particles and the area S1 of the portion where the fine particles exist is less than 10%, the thermal conductivity is hardly improved and remains at 5.1 W / mK. On the other hand, when S1 / S exceeded 10%, 5.5 to 6.2 W / mK and a high thermal conductive sheet could be obtained.
表２に示す粒径の大径アルミナ球状粒子と微細アルミナ不定形粒子を、体積比で90：10となるように混合機にて1時間混合した後、表２に示す熱処理温度×1時間大気中で熱処理を施し、得られたアルミナ粒子を用いて、実施例１と同様に各特性を測定した。
（Gr.5：熱処理温度）
Gr.5の発明例は、熱処理温度を変化させたものである。
After mixing large-diameter spherical spherical particles having the particle size shown in Table 2 and fine alumina amorphous particles in a mixer so that the volume ratio is 90:10 for 1 hour, the heat treatment temperature shown in Table 2 × air for 1 hour Each of the properties was measured in the same manner as in Example 1 using the alumina particles obtained by heat treatment.
(Gr.5: Heat treatment temperature)
In the invention example of Gr.5, the heat treatment temperature is changed.
1100℃の熱処理では、付着部が2％と十分に得られずに熱伝導率が5.0W/mK止まりであった。 In the heat treatment at 1100 ° C., the adhered portion was not sufficiently obtained as 2%, and the thermal conductivity was only 5.0 W / mK.
1550℃の熱処理では、付着部は十分にあるものの、スラリー粘度が10000Pa・s超と高くなり過ぎ、熱伝導率が向上せず、5.2W/mK止まりであった。 In the heat treatment at 1550 ° C., the adhering part was sufficient, but the slurry viscosity was too high, exceeding 10,000 Pa · s, the thermal conductivity was not improved, and it was only 5.2 W / mK.
1200〜1500℃の熱処理では、付着部が30％を超え、熱伝導率が5.8W/mK以上とさらに向上し、より好適な範囲となった。
（Gr.6：球状微細粒子）
Gr.6の発明例は、平均粒径35μｍの大径アルミナ粒子と平均粒径1.0μｍの微細アルミナ粒子を、1400℃の熱処理で付着させる微細粒子の形状を変化させたものである。発明例26は球状、発明例3は不定形である。球状粒子を付着させた場合、流動性が不定形粒子を付着させた場合より良く、スラリー粘度は低下した。熱伝導率は6.0W/mKと向上したが、不定形粒子の場合と比較するとやや低い値であった。
（Gr.7：熱処理なし）
大きな粒子と微細粒子を予め混合し熱処理するという工程を取らず、Gr.5と同じ体積比90：10になるように、樹脂と35μｍ粒子、1.0μｍ粒子を秤量し、1時間混合した後、シート成形を行なった。
In the heat treatment at 1200 to 1500 ° C., the adhered portion exceeded 30%, and the thermal conductivity was further improved to 5.8 W / mK or more, and became a more suitable range.
(Gr.6: Spherical fine particles)
The invention example of Gr. 6 is obtained by changing the shape of fine particles in which large-sized alumina particles having an average particle diameter of 35 μm and fine alumina particles having an average particle diameter of 1.0 μm are adhered by heat treatment at 1400 ° C. Invention Example 26 is spherical, and Invention Example 3 is indefinite. When spherical particles were attached, the fluidity was better than when amorphous particles were attached, and the slurry viscosity was reduced. Although the thermal conductivity improved to 6.0 W / mK, it was slightly lower than that of the amorphous particles.
(Gr.7: No heat treatment)
Without taking the process of premixing large particles and fine particles and heat-treating them, weigh the resin and 35μm particles and 1.0μm particles so that the volume ratio is 90:10, which is the same as Gr.5. Sheet molding was performed.
スラリーは突起がないため、粘度が低くなった。しかし、微細粒子が単独で存在しているため、樹脂が硬化阻害を起こし、シートを得ることができなかった。 Since the slurry had no protrusions, the viscosity was low. However, since the fine particles are present alone, the resin is inhibited from curing and a sheet cannot be obtained.
即ち、微細粒子が大きな粒子に付着していると、樹脂の硬化反応を進める触媒に影響を及ぼさなくなり、樹脂が硬化してシートを得ることができることが分かった。
That is, it was found that when fine particles are attached to large particles, the catalyst that promotes the curing reaction of the resin is not affected, and the resin is cured to obtain a sheet.
Claims (9)
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