JP2004338124A - Heat conductive sheet - Google Patents
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- JP2004338124A JP2004338124A JP2003134605A JP2003134605A JP2004338124A JP 2004338124 A JP2004338124 A JP 2004338124A JP 2003134605 A JP2003134605 A JP 2003134605A JP 2003134605 A JP2003134605 A JP 2003134605A JP 2004338124 A JP2004338124 A JP 2004338124A
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【０００１】
【発明の属する技術分野】
本発明は、プラズマディスプレイパネルや有機エレクトロルミネッセンスディスプレイの放熱板の間に介在され、これらの部材に発生した熱を放熱板へ伝導するための熱伝導シートに係り、特に、熱伝導シートの接着面積を維持して熱伝導率を向上させる熱伝導シートに関する。尚、本発明において樹脂組成物の配合組成を示す「部」等の単位は、特に断らない限り質量基準で表す。
【０００２】
【従来の技術】
近年、大画面で、薄型かつ軽量の画像表示措置としてプラズマディスプレイや有機エレクトロルミネッセンスディスプレイ（以下、表示パネルという）が実用化されている。この表示パネルは、発光表示する際に内部放電によって発熱し、局部的に伸縮して破損や画質劣化が生じてしまう。このため、表示パネルの背面に熱伝導シートを介在させて放熱板を取り付け、発生した熱を放熱させる手段が提案されている。この際に介在させる熱伝導シートとしては、アクリル系モノマーに熱伝導フィラーおよび重合開始剤を分散させた組成物をポリエステル等のフィルム上にナイフ塗工し、紫外線を塗工膜に照射し重合させて得られるシートが知られている（特許文献１参照）。
【０００３】
このような熱伝導シートを、剛直な板状体である放熱板又は表示パネルに貼付するには、柔軟性のある熱伝導シートを曲折させて気泡を追い出しながら貼り付けることにより、気泡を追い出しながら均一に接着することができるので、熱伝導シートと放熱板等との界面での十分な熱伝導が実現できる。しかしながらこのようにして得られた放熱板又は表示パネルと熱伝導シートの積層体を、もう一方の部材に貼り付ける際には、剛直な該積層体は曲げることができないため、貼り付け面を全面同時に押しつける事となり、両者の界面に気泡が巻き込まれて実質的な接着面積が大幅に減少すると共に、巻き込まれた気泡が断熱材となって熱伝導率が大幅に低減してしまうという課題があった。
【０００４】
【特許文献１】特開平１１−２９２９９８号公報
【発明が解決しようとする課題】
【０００５】
本発明は、表示パネルの背面に放熱板を固定する際に、これらの界面に巻き込まれた気泡を逃がすことで、実質的な接着面積を高く維持して界面での良好な熱伝導率が得られる熱伝導シートを提供することを課題とする。
【０００６】
【課題を解決するための手段】
本発明者は、上記に鑑み鋭意検討を行った結果、該熱伝導シートの表面に特定の感熱接着性表層を設ける事により、前記課題が解決できる事を見出し本発明に至った。
【０００７】
即ち本発明は、アクリル系共重合体に熱伝導フィラーを配合させた熱伝導性組成物をシート状に成形して得られた熱伝導基材と、該熱伝導基材の一面又は両面へ熱可塑性樹脂をシート状に成形して得られた感熱接着性表層を積層して得られる熱伝導シートにおいて、前記感熱接着性表層のうち少なくとも一方が、融点が４０℃〜１００℃であるワックス及び／又はパラフィンと、平均粒子径が２μｍ以上で球形又は不定形の熱伝導フィラー粉末からなる熱伝導シートである。又、前記感熱接着性表層の少なくとも一方が、融点が４０℃〜１００℃であるワックス及び／又はパラフィン、軟化点が４０℃〜１００℃である熱可塑性樹脂、及び粒子径が２μｍ以上で球形又は不定形の熱伝導フィラー粉末からなる熱伝導シートが好ましい。更に、前記感熱接着性表層の少なくとも一方が、前記ワックス及び／パラフィンと熱可塑性樹脂の合計を１００部としたときに、熱伝導フィラー粉末２０〜４００部を含有する熱伝導シートが好ましく、 前記熱伝導フィラー粉末が水酸化アルミニウムであることが特に好ましい。
【０００８】
【発明の実施の形態】
本発明の熱伝導シートは、熱伝導基材と、熱伝導基材の一面又は両面に積層された感熱接着性表層（以下単に「表層」という。）を有するものであり、表層が、表示パネルを動作状態にした時に発生する熱によって軟化、流動し、表示パネルの背面に放熱板を固定する際に巻き込まれた気泡を逃がすことで接着面積を拡大し、熱伝導率を向上させたことを特徴とするものである。
【０００９】
本発明の熱伝導基材は、アクリル系共重合体に熱伝導フィラーを配合させた熱伝導性組成物からなる。熱伝導基材に用いるアクリル系共重合体とは、アクリル酸、メタクリル酸、及びそれらの誘導体の２種以上からなる共重合体であり、一般的なものを適宜選択して採用でる。具体的には、メチル基、エチル基、プロピル基、ブチル基、イソオクチル基、イソノニル基、イソデシル基、ドデシル基、ラウリル基、トリデシル基、ペンタデシル基、ヘキサデシル基、ヘプタデシル基、オクタデシル基、ノナデシル基、及びエイコキシル基などの、炭素数が２０以下のアルキル基を有する（メタ）アクリル酸エステルの２種以上からなる共重合体が挙げられる。
【００１０】
又、一部の共重合成分として、アクリル酸ヒドロキエチル、メタクリル酸ヒドロキシエチル、アクリル酸ヒドリキシプロピル、メタクリル酸ヒドロキシプロピル、Ｎ―メチロールアクリルアミド、アクリロニトリル、メタクリロニトリル、アクリル酸グリシジル、酢酸ビニル、スチレン、イソプレン、ブタジエン、イソブチレン、及びビニルエーテル等の１種以上を含有したものであっても良い。
【００１１】
また、熱伝導基材に配合する熱伝導フィラーとしては、十分な熱伝導性を与える事のできるものであれば、一般的な無機フィラーを用いる事ができ、特に限定されるものではなくいが、具体例としては、アルミナ、水酸化アルミニウム、ボロンナイトライド、酸化珪素及び窒化アルミニウム等が挙げられる。中でも水酸化アルミニウムは難燃性が得られる点で特に好ましい。
【００１２】
これらのフィラーは、十分な熱伝導性を得る目的で、通常樹脂成分１００部に対して、５０部〜３００部程度配合される。これらのフィラーは、一般的な方法で樹脂と混合することができる。
【００１３】
又、この熱伝導基材には、必要に応じて本発明の目的を阻害しない範囲で、改質剤、老化防止剤、熱安定剤、着色剤、難燃剤などを添加しても良い。
【００１４】
前記のアクリル系共重合体にこれらのフィラーを混合した樹脂組成物を、例えば、ドクターブレードやコンマロール等の方法でシート状に加工することにより、熱伝導基材を得る事ができる。熱伝導基材の厚さは、固定する表示パネルや放熱板の大きさに準じて適宜選択すれば良いが、一般的には０．５ｍｍ〜３ｍｍ、熱伝導率は０．４ｗ／ｍ・ｋ以上であることが好ましい。また、この熱伝導基材は、その使用目的に応じて、異なる樹脂組成物の多層構成からなるものであってもよい。
【００１５】
本発明の表層は、融点が４０℃〜１００℃のワックス及び／又はパラフィンなどの流動化剤に、平均粒子径が２μｍ以上で、球形又は不定形の熱伝導フィラー粉末を分散させた混合物を用いることができる。ワックス等の融点が、１００℃を越えると流動性が十分でないことにより、表示パネル等に熱伝導シートを貼付する際に十分密着させることができず、接着面積を十分に高めることができない。又一方で熱伝導シートを表示パネル等に貼付して使用する際に、表示パネルからの熱伝導で熱伝導シートも１００℃程度までの範囲で温度上昇するが、前記のワックス及び／又はパラフィンの融点が４０℃未満であると、その際に表層が流出し空隙が発生し熱伝導が悪くなる。一方、融点が１００℃以上では軟質化状態にならず初期接着時に生じた空隙が埋まらず熱伝導性が改善されない。即ち本発明において、表層として、融点が４０℃〜１００℃のワックス及び／又はパラフィンなどの流動化剤を用いる事により、この熱伝導シートを表示パネル等に貼付して使用する際に、その温度上昇に伴って密着性が改善され、その結果として熱伝導性が向上することも極めて重要である。
【００１６】
表層は例えば、ドクターブレードやコンマロール等の方法で、前記のシート状に形成することができる。一方で、このシート化工程での熱伝導フィラーの均一分散性が良好で製膜性が良いという点で、表層は、前記の成分に加えて、ＪＩＳＫ７２０６（ビカット軟化温度試験）に準拠して測定した軟化温度が、４０〜１００℃の熱可塑性樹脂成分を添加した混合物が好ましい。該熱可塑性樹脂の軟化温度が、前記の範囲が好ましい理由は、前記のワックス及び／又はパラフィンの融点の場合と同様である。この熱可塑性樹脂としては、前記軟化温度が、４０〜１００℃の樹脂で有れば特に限定されるものではないが、流動性の点でプロピレン系樹脂、エチレン系樹脂、エチレン−α−オレフィン系重合体、エチレン−酢酸ビニル共重合体などが好ましい。又、これらの熱可塑性樹脂の添加量は、製膜性の観点から適宜設定すれば良いが、ワックス等と熱可塑性樹脂からなる有機物の合計を１００部としたとき、５０部以上の範囲で用いるのが一般的である。
【００１７】
又、表層には、前記の軟化温度や加工性を損なわない範囲で、熱伝導性フィラーを配合して用いる。このことによって表層の熱伝導度を増加させ、熱伝導シート全体の熱伝導効率を向上させることができる。
【００１８】
表層に配合する熱伝導フィラーとしては、一般的なものを適宜選択して採用できるが、熱伝導性に優れていて、樹脂との分散性が良いと言う点でアルミナ、水酸化アルミニウム、ボロンナイトライド、酸化珪素及び窒化アルミニウム等が好ましい。特に水酸化アルミニウムは難燃性が得られる点で好ましい。これらのフィラーは、一般的な方法で有機物成分と混合することができる。
【００１９】
これらの熱伝導フィラーは、その形状が球形又は不定形で、その平均粒子径が２μｍ以上のものを用いる。平均粒子径が２μｍ未満のものを用いると、得られた熱伝導シートを表示パネル等に貼付するときの接着性（タック性）が不十分となる。 又、これらのフィラーの配合量は、有機物成分１００部に対して２０〜４００部が好ましい。２０部未満では熱伝導シートの熱伝導性が不十分となる恐れが有り、４００部を越えると、熱伝導シートを表示パネル又は放熱板に折り曲げて貼付する際に、表層の表面にクラックが発生したり、一方で、表層を、もう一方の表示パネル又は放熱板に熱接着する際の接着性が不十分で、十分な接着ができない場合が有る。
【００２０】
又、表層には、必要に応じて本発明の目的を阻害しない範囲で、改質剤、老化防止剤、熱安定剤、着色剤、難燃剤などを添加しても良い。
【００２１】
本発明の熱伝導シートは、表層により、表示パネル又は放熱板の表面に貼付されて用いられるが、この表層は、表示パネルを動作状態にした時に発生する熱によって軟化して流動し、表示パネルの背面に放熱板を固定する際に巻き込まれた気泡を逃がす役割を果たす。このことが本発明極めて重要である。
【００２２】
表層の厚さは、固定する表示パネルや放熱板の大きさに準じて適宜選択すれば良い。ただし、厚さがあまりに厚いと表層自体が断熱層となって熱伝導率が低下してしまい、あまりに薄いと巻き込まれた気泡を逃がすことができなくなって接着面積が減少してしまうため、表層の厚さは１０〜３００μｍが好ましく、さらに好ましくは３０〜２００μｍである。
【００２３】
本発明の熱伝導シートは、例えば以下の製法によって製造することができる。まず、アクリル系共重合体に熱伝導フィラーを配合した樹脂組成物を、シリコーンなどで離型処理されたポリエステルフィルム上に前記の熱伝導性樹脂組成物をドクターブレードやコンマロール等の方法で塗布することにより、シート状に形成して熱伝導基材を作成し、この熱伝導基材の一面又は両面に、前記の感熱接着表層をシート状に成形して積層して、熱伝導シートが得られる。
【００２４】
なお、本発明の熱伝導シートにおいて、熱伝導基材の一面のみに表層を有するものを用いる場合は、表示パネル又は放熱板の、初めに貼り付ける部材に、熱伝導シートのタック力を利用して表層を有さない面を、貼り付けることが望ましい。即ち、初めに貼り付ける際は、前記のように柔軟性のある熱伝導シートを曲折させて気泡を追い出しながら貼り付けることにより、気泡を追い出しながら均一に接着することができ、熱伝導シートと放熱板等との界面での十分な熱伝導が実現できる。そのようにして得られた、表示パネル又は放熱板と熱伝導シートを積層したものを、他の部材（表示パネル又は放熱板）の表面に、表層の側を、表示パネルに問題を生じない程度の適切な圧力で圧着することにより、前記のような良好な熱伝導性を有する表示パネルと放熱板の積層体が得られる。
【００２５】
熱伝導基材の両面に該表層を有する熱伝導性シートの場合には、表示パネル、熱伝導シート及び放熱板を順次重ねておいて、適切な圧力で加圧し接着することで、良好な熱伝導性を有する表示パネルと放熱板の積層体が得られる。
【００２６】
【実施例】
本発明を実施例により、更に具体的に説明する。
（評価方法）
本発明の特性評価は以下の評価法で行った。尚、これらの評価法は、本発明の効果を示す為の方法の一例を示すものである。
【００２７】
１．接着割合の評価
片面に表層を設けた熱伝導シートについては、アルミニウム板に、熱伝導シートの表層のない側の面を、空気が入らないように曲折しながら張り付け、２ｋｇのローラで１往復させ圧着させた後、熱伝導シートの表層上に縦２１０ｍｍ、横３００ｍｍ、厚さ５ｍｍのガラス板を静かに載置し、８０℃で７２時間養生させて積層し試験片を得た。又、両面に表層を設けた熱伝導シートについても、アルミニウム板に、表層の一方の面を貼付した以外は、同様にして試験片を作成した。次にこれらの試験片のガラスと熱伝導シートの貼り付け面を、７０℃で１時間予備加熱し表層を軟質化させ、接着面積を拡大した後に接着面積をガラスを通してデジタルカメラにて写真撮影し、画像処理して得られた画像ドット数から接着割合を算出した。
【００２８】
２．熱伝導率
本発明における熱伝導率は、まずシート化した熱伝導性組成物をＴＯ−３型銅製ヒーターケースと銅板の間に０．３４ＭＰａの圧力かかるようにネジ止めした後、ヒーターケースと銅板が５５℃になるまで加熱し、さらにそれらを室温まで冷却した後、ヒーターケースと銅板との温度差が０．１℃以下になることを確認した後、ヒーターケースに電力１５Ｗをかけて４分間保持した際における銅製ヒーターケースと銅板の温度差を測定し、下記（１）式により算出した。
【００２９】
【式１】
得られた熱抵抗の値をもとに下記（２）式により熱伝導率を算出した。なお、ここで試料の厚みは熱抵抗測定時の厚み（試料に０．３４ＭＰａの圧力かかるようにネジ止めした後、ヒーターケースと銅板が５５℃になるまで加熱し、さらにそれらを室温まで冷却した時の試料厚み）である。また伝熱面積はＴＯ−３型の伝熱面積０．０００６ｍ２である。
【００３１】
【式２】
３．折り曲げ性の評価
熱伝導シートを表示パネル及び放熱板へ貼り付ける際に発生する表層のひび割れの状態を、目視にて下記の基準で評価した。ひび割れが発生すると表示パネルや放熱板へ貼つける時に凹凸が発生して熱抵抗が大きくなる。
○：シートを９０度の角度で折り曲げた時に表層の表面に割れが生じない。
×：シートを９０度の角度で折り曲げた時に表層の表面に割れが生じる。
４．タック性の評価
熱伝導シートを表示パネル及び放熱板へ貼り付ける際の、表層の粘着性をニチバン株式会社製 ＮＳプローブタックテスターを用いてタック値のピーク値を測定し、下記の基準で評価した。タック力が微少な場合は熱伝導シートを表示パネルや放熱板へ固定できない。
○：プローブタック試験機のピーク値が０．５Ｎ／２０ｍｍ２以上。
×：プローブタック試験機のピーク値が０．５Ｎ／２０ｍｍ２以下。
５．接着状態の評価
熱伝導シートを表示パネル及び接着性は加熱時に表層が軟化して接着部分から流れ出しの有無を下記の基準で判定した。流出すると接着面積が減少して熱抵抗が大きくなる。
○： 接着部分が加熱により流動し、時間の経過とともに表層が接着部分より外に流出せず接着面積が低下しない。
△： 接着部分が加熱により流動はしないが、接着面積があまり改善されない。
×： 接着部分が加熱により流動し、時間の経過とともに表層が接着部分より外に流出し接着面積が低下する。
【００３３】
（実施例１）
アクリル系共重合体を水に分散させたエマルジョン（高圧ガス工業株式会社製ぺガール８５１；樹脂成分５５％）の樹脂成分１００部に対して、熱伝導フィラーとして、水酸化アルミニウム（昭和電工株式会社製 Ｈ−３２）を１３５部配合した熱伝導性組成物を混合し、その後ドクターブレードやコンマロール等の方法でシート状に塗工し、その後さらに乾燥の加工をおこない、９００μｍのシート状の熱伝導基材を得た。次に、感熱接着性表層として、エチレン−酢酸ビニル共重合体樹脂「三井・デュポンポリケミカル社製 エバフレックスＥＶ１５０」を１００部と日本精蝋社製「パラフィンワックス１１５（融点４７℃）」をエチレン−酢酸ビニル共重合体樹脂に対して４０部を、トルエン溶剤４００部（エチレン−酢酸ビニル共重合体樹脂に対して）の中で均一になるまで混合した。その混合物中の固形分量１００部に対して熱伝導フィラーである水酸化アルミニウム「昭和電工株式会社製 Ｈ−３２」を５０部混合し、スラリー状物を得た。その後、シリコーン離型処理したポリエステルフィルム上に前記の熱可塑性樹脂組成物を、ドクターブレード方法で塗布することにより、シート状に形成し厚さ１００μｍの表層を形成し、前記熱伝導基材の片面にドライラミネート法で積層し熱伝導シートとした。このシートを用いて前記の評価を行い、その結果を表１に示した。
【００３４】
【表１】
（実施例２）
厚さ９００μｍの熱伝導基材の両面に、厚さ５０μｍの感熱接着性表層を形成した以外は、実施例１と同様にして熱伝導シートを作成し同様の評価を行い、表１に結果を示した。
【００３６】
（実施例３）
厚さ９００μｍの熱伝導基材の片面に積層する感熱接着性表層の熱伝導フィラーである水酸化アルミニウム「昭和電工株式会社製 Ｈ−３２」を３５０部混合した以外は、実施例１と同様にして熱伝導シートを作成し同様の評価を行い、表１に結果を示した。
【００３７】
（比較例１）
アクリル系共重合体を水に分散させたエマルジョン（高圧ガス工業株式会社製ぺガール８５１；樹脂成分５５％）の樹脂成分１００部に対して、熱伝導フィラーとして、水酸化アルミニウム（昭和電工株式会社製 Ｈ−３２）を１３５部配合した熱伝導性組成物を、成形、乾燥し１０００μｍのシート状の熱伝導シートを得た。その後、感熱接着性表層は積層しなかった。表１に結果を示す。本比較例では良好な接着割合及び熱伝導率が得られなかった。
【００３８】
（比較例２）
感熱接着性表層のエチレン−酢酸ビニル共重合体樹脂を「三井・デュポンポリケミカル社製 エバフレックス ＭＦＲ１５０で酢酸ビニル含有量が２２％の軟化温度が３０℃の樹脂」に変更した以外は、実施例１と同様にして熱伝導シートを作成し同様の評価を行なった。表１に結果を示した。加熱状態での使用時に表層が液状化し流れ出して、目的とする接着割合、熱伝導度が得られなかった。
【００３９】
（比較例３）
厚さ９００μｍの熱伝導基材の片面に積層する感熱接着性表層の熱伝導フィラーである水酸化アルミニウム「昭和電工株式会社製 Ｈ−３２」を、平均粒子径を０．５μｍにした以外は、実施例１と同様にして熱伝導シートを作成し同様の評価を行なった。表１に結果を示す。表層の剛性が上がりすぎて、熱伝導シートとガラス板の界面が剥離してしまい、目的とする熱伝導率とタック性が得られなかった。
【００４０】
【発明の効果】
本発明の熱伝導シートは、表示パネルの背面に放熱板を固定する際に、これらの界面に巻き込まれた気泡を効果的に逃がすことができ、接着面積を拡大し、接着面積を維持して熱伝導率を向上させた熱伝導シートを提供することができる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a heat conductive sheet that is interposed between heat radiating plates of a plasma display panel or an organic electroluminescent display and conducts heat generated in these members to the heat radiating plate, and in particular, maintains an adhesive area of the heat conductive sheet. And a heat conductive sheet for improving heat conductivity. In the present invention, units such as "parts" indicating the composition of the resin composition are expressed on a mass basis unless otherwise specified.
[0002]
[Prior art]
2. Description of the Related Art In recent years, a plasma display and an organic electroluminescence display (hereinafter, referred to as a display panel) have been put into practical use as a large-screen, thin and lightweight image display device. This display panel generates heat due to internal discharge when performing luminous display, and is locally expanded and contracted to cause damage and image quality deterioration. For this reason, a means has been proposed in which a heat radiating plate is attached to the rear surface of the display panel with a heat conductive sheet interposed therebetween to radiate generated heat. As a heat conductive sheet to be interposed at this time, a composition in which a heat conductive filler and a polymerization initiator are dispersed in an acrylic monomer is knife-coated on a film of polyester or the like, and ultraviolet rays are applied to the coated film to polymerize the film. A sheet obtained by this method is known (see Patent Document 1).
[0003]
In order to attach such a heat conductive sheet to a heat radiating plate or a display panel that is a rigid plate-like body, the flexible heat conductive sheet is bent and attached while expelling air bubbles, thereby expelling air bubbles. Since uniform bonding can be achieved, sufficient heat conduction at the interface between the heat conductive sheet and the heat radiating plate or the like can be realized. However, when the laminated body of the heat sink or the display panel and the heat conductive sheet obtained in this manner is attached to another member, the rigid laminated body cannot be bent. At the same time, there is a problem that air bubbles are trapped at the interface between the two and the substantial bonding area is significantly reduced, and the trapped air bubbles become a heat insulating material and the thermal conductivity is greatly reduced. Was.
[0004]
[Patent Document 1] JP-A-11-292998 [Problems to be Solved by the Invention]
[0005]
According to the present invention, when a heat sink is fixed to the back surface of a display panel, air bubbles trapped at these interfaces are released, thereby maintaining a substantially high bonding area and obtaining good thermal conductivity at the interfaces. It is an object to provide a heat conductive sheet that can be used.
[0006]
[Means for Solving the Problems]
As a result of intensive studies in view of the above, the present inventor has found that the above-mentioned problem can be solved by providing a specific heat-sensitive adhesive surface layer on the surface of the heat conductive sheet, and has reached the present invention.
[0007]
That is, the present invention relates to a heat conductive substrate obtained by molding a heat conductive composition obtained by blending a heat conductive filler with an acrylic copolymer into a sheet, and applying heat to one or both surfaces of the heat conductive substrate. In a heat conductive sheet obtained by laminating a heat-sensitive adhesive surface layer obtained by molding a plastic resin into a sheet, at least one of the heat-sensitive adhesive surface layers has a melting point of 40 ° C to 100 ° C and / or wax. Alternatively, the thermal conductive sheet is composed of paraffin and a spherical or amorphous thermal conductive filler powder having an average particle diameter of 2 μm or more. Further, at least one of the heat-sensitive adhesive surface layers has a melting point of 40 ° C. to 100 ° C., a wax and / or paraffin, a softening point of 40 ° C. to 100 ° C., a thermoplastic resin, and a spherical particle having a particle diameter of 2 μm or more. A heat conductive sheet made of an amorphous heat conductive filler powder is preferable. Further, when at least one of the heat-sensitive adhesive surface layers has a total of 100 parts of the wax and / or paraffin and the thermoplastic resin, a heat conductive sheet containing 20 to 400 parts of a heat conductive filler powder is preferable. It is particularly preferred that the conductive filler powder is aluminum hydroxide.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
The heat conductive sheet of the present invention has a heat conductive base material and a heat-sensitive adhesive surface layer (hereinafter, simply referred to as “surface layer”) laminated on one or both surfaces of the heat conductive base material, and the surface layer is a display panel. Is softened and flowed by the heat generated when the device is in the operating state, and the air bubbles trapped when the heat sink is fixed to the back of the display panel are expanded to increase the bonding area and improve the thermal conductivity. It is a feature.
[0009]
The heat conductive substrate of the present invention is made of a heat conductive composition in which a heat conductive filler is blended with an acrylic copolymer. The acrylic copolymer used for the heat conductive substrate is a copolymer composed of two or more of acrylic acid, methacrylic acid, and derivatives thereof, and a general one is appropriately selected and employed. Specifically, methyl, ethyl, propyl, butyl, isooctyl, isononyl, isodecyl, dodecyl, lauryl, tridecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, And a copolymer of two or more (meth) acrylates having an alkyl group having 20 or less carbon atoms, such as an eicoxyl group.
[0010]
Also, as a part of copolymerization components, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, N-methylolacrylamide, acrylonitrile, methacrylonitrile, glycidyl acrylate, vinyl acetate, styrene , Isoprene, butadiene, isobutylene, vinyl ether and the like.
[0011]
In addition, as the heat conductive filler to be mixed with the heat conductive base material, a general inorganic filler can be used as long as it can provide sufficient heat conductivity, and is not particularly limited. Specific examples include alumina, aluminum hydroxide, boron nitride, silicon oxide, and aluminum nitride. Among them, aluminum hydroxide is particularly preferred in that flame retardancy can be obtained.
[0012]
These fillers are usually added in an amount of about 50 to 300 parts with respect to 100 parts of the resin component for the purpose of obtaining sufficient thermal conductivity. These fillers can be mixed with the resin in a general manner.
[0013]
If necessary, a modifier, an antioxidant, a heat stabilizer, a coloring agent, a flame retardant, and the like may be added to the heat conductive substrate as long as the object of the present invention is not impaired.
[0014]
A heat conductive substrate can be obtained by processing a resin composition obtained by mixing the above-mentioned filler with the acrylic copolymer, for example, by using a method such as a doctor blade or a comma roll. The thickness of the heat conductive substrate may be appropriately selected according to the size of the display panel or heat sink to be fixed, but is generally 0.5 mm to 3 mm, and the heat conductivity is 0.4 w / m · k. It is preferable that it is above. Further, the heat conductive substrate may have a multilayer structure of different resin compositions depending on the purpose of use.
[0015]
The surface layer of the present invention uses a mixture of a fluidizing agent such as wax and / or paraffin having a melting point of 40 ° C to 100 ° C and a spherical or amorphous heat conductive filler powder having an average particle diameter of 2 µm or more dispersed therein. be able to. If the melting point of the wax or the like exceeds 100 ° C., the fluidity is not sufficient, so that the heat conductive sheet cannot be sufficiently adhered to the display panel or the like when it is attached, and the adhesion area cannot be sufficiently increased. On the other hand, when the heat conductive sheet is attached to a display panel or the like and used, the temperature of the heat conductive sheet rises up to about 100 ° C. due to heat conduction from the display panel. When the melting point is lower than 40 ° C., the surface layer flows out at that time, voids are generated, and heat conduction is deteriorated. On the other hand, if the melting point is 100 ° C. or more, the softened state is not obtained, the voids generated at the time of initial bonding are not filled, and the thermal conductivity is not improved. That is, in the present invention, by using a fluidizing agent such as wax and / or paraffin having a melting point of 40 ° C. to 100 ° C. as a surface layer, when the heat conductive sheet is attached to a display panel or the like and used, the temperature is lowered. It is also very important that the adhesion is improved as the temperature rises, and consequently the thermal conductivity is improved.
[0016]
The surface layer can be formed into the above-mentioned sheet shape by, for example, a method using a doctor blade or a comma roll. On the other hand, the surface layer is measured in accordance with JIS K7206 (Vicat softening temperature test) in addition to the components described above, in that the uniform dispersion of the heat conductive filler and the film forming property are good in the sheet forming step. A mixture to which a thermoplastic resin component having a softening temperature of 40 to 100 ° C. is added is preferable. The reason why the softening temperature of the thermoplastic resin is preferably in the above range is the same as in the case of the melting point of wax and / or paraffin described above. The thermoplastic resin is not particularly limited as long as the softening temperature is a resin having a temperature of 40 to 100 ° C., but in terms of fluidity, a propylene resin, an ethylene resin, and an ethylene-α-olefin resin are used. Polymers and ethylene-vinyl acetate copolymers are preferred. Further, the addition amount of these thermoplastic resins may be appropriately set from the viewpoint of film-forming properties, but when the total of the organic substance composed of the wax or the like and the thermoplastic resin is 100 parts, it is used in a range of 50 parts or more. It is common.
[0017]
In the surface layer, a heat conductive filler is blended and used within a range that does not impair the above-mentioned softening temperature and workability. Thereby, the heat conductivity of the surface layer can be increased, and the heat transfer efficiency of the entire heat conductive sheet can be improved.
[0018]
As the heat conductive filler to be blended in the surface layer, a general one can be appropriately selected and employed, but alumina, aluminum hydroxide, boron nitride and the like are excellent in heat conductivity and good in dispersibility with resin. Ride, silicon oxide and aluminum nitride are preferred. Particularly, aluminum hydroxide is preferable in that flame retardancy can be obtained. These fillers can be mixed with organic components in a general manner.
[0019]
These heat conductive fillers have a spherical or irregular shape and an average particle diameter of 2 μm or more. When the average particle diameter is less than 2 μm, the adhesiveness (tackiness) when the obtained heat conductive sheet is attached to a display panel or the like becomes insufficient. The amount of these fillers is preferably 20 to 400 parts per 100 parts of the organic component. If it is less than 20 parts, the thermal conductivity of the heat conductive sheet may be insufficient. If it exceeds 400 parts, cracks may occur on the surface of the surface layer when the heat conductive sheet is bent and attached to a display panel or a heat sink. On the other hand, in some cases, the adhesiveness at the time of thermally bonding the surface layer to the other display panel or the heat radiating plate is insufficient, and sufficient bonding may not be performed.
[0020]
If necessary, a modifier, an antioxidant, a heat stabilizer, a coloring agent, a flame retardant, etc. may be added to the surface layer as long as the object of the present invention is not impaired.
[0021]
The heat conductive sheet of the present invention is used by being adhered to the surface of a display panel or a radiator plate by a surface layer, and this surface layer is softened and flows by heat generated when the display panel is in an operating state, and the display panel is used. When the heat sink is fixed to the back of the device, it plays a role in releasing air bubbles trapped. This is very important in the present invention.
[0022]
The thickness of the surface layer may be appropriately selected according to the size of the display panel or heat sink to be fixed. However, if the thickness is too large, the surface layer itself becomes a heat insulating layer and the thermal conductivity decreases.If the thickness is too small, it becomes impossible to escape the trapped air bubbles and the bonding area decreases, so the surface area of the surface layer is reduced. The thickness is preferably from 10 to 300 μm, more preferably from 30 to 200 μm.
[0023]
The heat conductive sheet of the present invention can be manufactured by, for example, the following manufacturing method. First, a resin composition in which a heat conductive filler is blended with an acrylic copolymer is applied to a polyester film that has been release-treated with silicone or the like by using a method such as a doctor blade or a comma roll. By doing so, a heat conductive base material is formed by forming a sheet, and the heat-sensitive adhesive surface layer is formed into a sheet shape and laminated on one or both surfaces of the heat conductive base material to obtain a heat conductive sheet. Can be
[0024]
In the case of using a heat conductive sheet having a surface layer only on one surface of the heat conductive base material, the tacking force of the heat conductive sheet is used for the first member to be attached to the display panel or heat sink. It is desirable to attach a surface having no surface layer. That is, at the time of attaching first, the flexible heat conductive sheet is bent as described above, and is attached while expelling bubbles, so that the air bubbles can be uniformly adhered while expelling air bubbles, and the heat conduction sheet and the heat radiation can be radiated. Sufficient heat conduction at the interface with the plate or the like can be realized. The display panel or the heat radiating plate and the heat conductive sheet thus obtained are laminated on the surface of another member (the display panel or the heat radiating plate), and the surface layer side is in such a degree that no problem occurs in the display panel. By performing pressure bonding under an appropriate pressure, a laminate of a display panel and a heat sink having good thermal conductivity as described above can be obtained.
[0025]
In the case of a heat conductive sheet having the surface layer on both sides of a heat conductive base material, a display panel, a heat conductive sheet and a heat sink are sequentially stacked, and a good heat is applied by pressing and bonding with an appropriate pressure. A laminate of a display panel and a heat sink having conductivity is obtained.
[0026]
【Example】
The present invention will be described more specifically with reference to examples.
(Evaluation method)
The characteristics of the present invention were evaluated by the following evaluation methods. Note that these evaluation methods show one example of a method for showing the effects of the present invention.
[0027]
1. Evaluation of Adhesion Ratio For a heat conductive sheet having a surface layer on one side, the surface of the heat conductive sheet on the side without the surface layer was attached to an aluminum plate while bending so that air did not enter, and was reciprocated once with a 2 kg roller. After pressure bonding, a 210 mm long, 300 mm wide, 5 mm thick glass plate was gently placed on the surface layer of the heat conductive sheet, cured at 80 ° C. for 72 hours, and laminated to obtain a test piece. In addition, a test piece was prepared in the same manner for a heat conductive sheet having a surface layer on both sides, except that one surface of the surface layer was attached to an aluminum plate. Next, the surfaces of these test pieces to which the glass and the heat conductive sheet were bonded were preheated at 70 ° C. for 1 hour to soften the surface layer, and the bonding area was enlarged. The adhesion ratio was calculated from the number of image dots obtained by the image processing.
[0028]
2. Thermal Conductivity The thermal conductivity in the present invention is determined by first screwing the sheet-shaped thermal conductive composition between the TO-3 type copper heater case and the copper plate so as to apply a pressure of 0.34 MPa, and then heating the sheet with the heater case and the copper plate. Is heated to 55 ° C. and further cooled to room temperature. After confirming that the temperature difference between the heater case and the copper plate is 0.1 ° C. or less, 15 W of power is applied to the heater case for 4 minutes. The temperature difference between the copper heater case and the copper plate when it was held was measured and calculated by the following equation (1).
[0029]
(Equation 1)
The thermal conductivity was calculated by the following equation (2) based on the value of the obtained thermal resistance. Here, the thickness of the sample was the thickness at the time of measuring the thermal resistance (after the sample was screwed so as to apply a pressure of 0.34 MPa, the heater case and the copper plate were heated to 55 ° C., and then cooled to room temperature. Sample thickness at the time). The heat transfer area is a TO-3 type heat transfer area of 0.0006 m 2 .
[0031]
[Equation 2]
3. Evaluation of bending property The state of cracks in the surface layer generated when the heat conductive sheet was attached to the display panel and the heat sink was visually evaluated according to the following criteria. When cracks occur, irregularities occur when they are attached to a display panel or a heat sink, and the thermal resistance increases.
：: No crack is generated on the surface of the surface layer when the sheet is bent at an angle of 90 degrees.
X: Cracks occur on the surface of the surface layer when the sheet is bent at an angle of 90 degrees.
4. Evaluation of tackiness When sticking a heat conductive sheet to a display panel and a heat sink, the tackiness of the surface layer was measured by measuring the peak tack value using an NS probe tack tester manufactured by Nichiban Co., Ltd. and evaluated according to the following criteria. . When the tacking force is small, the heat conductive sheet cannot be fixed to the display panel or the heat sink.
：: The peak value of the probe tack tester was 0.5 N / 20 mm 2 or more.
×: The peak value of the probe tack tester was 0.5 N / 20 mm 2 or less.
5. Evaluation of Adhesion State The display panel and the adhesiveness of the heat conductive sheet were evaluated based on the following criteria as to whether or not the surface layer softened during heating and flowed out of the adhesion portion. When it flows out, the bonding area decreases and the thermal resistance increases.
：: The bonded portion flows by heating, and the surface layer does not flow out of the bonded portion over time, and the bonded area does not decrease with time.
Δ: The bonded portion does not flow due to heating, but the bonded area is not significantly improved.
×: The bonded portion flows due to heating, and the surface layer flows out of the bonded portion over time, and the bonded area is reduced.
[0033]
(Example 1)
Aluminum hydroxide (Showa Denko Co., Ltd.) was used as a heat-conductive filler for 100 parts of the resin component of an emulsion in which an acrylic copolymer was dispersed in water (Gall 851 manufactured by Kokon Gas Co., Ltd .; resin component 55%). H-32) was mixed with 135 parts of a heat conductive composition, and then applied in the form of a sheet using a method such as a doctor blade or a comma roll. A conductive substrate was obtained. Next, as a heat-sensitive adhesive surface layer, 100 parts of an ethylene-vinyl acetate copolymer resin “Evaflex EV150 manufactured by DuPont-Mitsui Polychemicals” and “Paraffin Wax 115 (melting point 47 ° C.)” manufactured by Nippon Seiwa Co., Ltd. -40 parts by weight of vinyl acetate copolymer resin were mixed in 400 parts of toluene solvent (relative to ethylene-vinyl acetate copolymer resin) until homogeneous. 50 parts of aluminum hydroxide "H-32 manufactured by Showa Denko KK" as a heat conductive filler was mixed with 100 parts of the solid content in the mixture to obtain a slurry. Thereafter, the thermoplastic resin composition is applied on a silicone release-treated polyester film by a doctor blade method, thereby forming a sheet-like surface layer having a thickness of 100 μm. Was laminated by a dry lamination method to obtain a heat conductive sheet. The evaluation was performed using this sheet, and the results are shown in Table 1.
[0034]
[Table 1]
(Example 2)
A heat conductive sheet was prepared and evaluated in the same manner as in Example 1 except that a heat-sensitive adhesive surface layer having a thickness of 50 μm was formed on both surfaces of a heat conductive base material having a thickness of 900 μm. Indicated.
[0036]
(Example 3)
The same procedure as in Example 1 was repeated except that 350 parts of aluminum hydroxide “H-32 manufactured by Showa Denko KK” as a heat conductive filler of the heat-sensitive adhesive layer to be laminated on one surface of the heat conductive base material having a thickness of 900 μm was mixed. A heat conductive sheet was prepared in the same manner as above, and the same evaluation was performed.
[0037]
(Comparative Example 1)
Aluminum hydroxide (Showa Denko Co., Ltd.) was used as a heat-conductive filler for 100 parts of the resin component of an emulsion in which an acrylic copolymer was dispersed in water (Gall 851 manufactured by Kokon Gas Co., Ltd .; resin component 55%). The heat conductive composition containing 135 parts of H-32) was molded and dried to obtain a 1000 μm sheet heat conductive sheet. Thereafter, the heat-sensitive adhesive surface layer was not laminated. Table 1 shows the results. In this comparative example, a good adhesion ratio and thermal conductivity were not obtained.
[0038]
(Comparative Example 2)
Example 1 Except that the ethylene-vinyl acetate copolymer resin of the heat-sensitive adhesive surface layer was changed to “a resin having a 22% vinyl acetate content and a softening temperature of 30 ° C. with Evaflex MFR150 manufactured by DuPont-Mitsui Polychemicals Co.” A heat conductive sheet was prepared in the same manner as in Example 1, and the same evaluation was performed. Table 1 shows the results. When used in a heated state, the surface layer was liquefied and flowed out, and the desired adhesion ratio and thermal conductivity could not be obtained.
[0039]
(Comparative Example 3)
Aluminum hydroxide as a heat conductive filler of a heat-sensitive adhesive surface layer to be laminated on one surface of a heat conductive base material having a thickness of 900 μm, and aluminum hydroxide `` H-32 manufactured by Showa Denko Co., Ltd. '' A heat conductive sheet was prepared in the same manner as in Example 1, and the same evaluation was performed. Table 1 shows the results. The rigidity of the surface layer was too high, and the interface between the heat conductive sheet and the glass plate was separated, so that the desired thermal conductivity and tackiness could not be obtained.
[0040]
【The invention's effect】
The heat conductive sheet of the present invention, when fixing the heat sink to the back surface of the display panel, can effectively release the air bubbles trapped at the interface between them, expanding the bonding area and maintaining the bonding area. A thermal conductive sheet with improved thermal conductivity can be provided.
Claims (4)
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| JP2003134605A JP4201640B2 (en) | 2003-05-13 | 2003-05-13 | Heat conduction sheet |
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| JP2003134605A JP4201640B2 (en) | 2003-05-13 | 2003-05-13 | Heat conduction sheet |
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| JP4201640B2 JP4201640B2 (en) | 2008-12-24 |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2007246664A (en) * | 2006-03-15 | 2007-09-27 | Polymatech Co Ltd | Heat conductive sheet |
| JP2009241440A (en) * | 2008-03-31 | 2009-10-22 | Polymatech Co Ltd | Heat-conductive sheet and its producing method |
| JP2013062379A (en) * | 2011-09-13 | 2013-04-04 | Nitto Denko Corp | Thermally conductive sheet and method for manufacturing the same |
-
2003
- 2003-05-13 JP JP2003134605A patent/JP4201640B2/en not_active Expired - Fee Related
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2007246664A (en) * | 2006-03-15 | 2007-09-27 | Polymatech Co Ltd | Heat conductive sheet |
| JP2009241440A (en) * | 2008-03-31 | 2009-10-22 | Polymatech Co Ltd | Heat-conductive sheet and its producing method |
| JP2013062379A (en) * | 2011-09-13 | 2013-04-04 | Nitto Denko Corp | Thermally conductive sheet and method for manufacturing the same |
Also Published As
| Publication number | Publication date |
|---|---|
| JP4201640B2 (en) | 2008-12-24 |
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