JP4201640B2 - Heat conduction sheet - Google Patents
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- JP4201640B2 JP4201640B2 JP2003134605A JP2003134605A JP4201640B2 JP 4201640 B2 JP4201640 B2 JP 4201640B2 JP 2003134605 A JP2003134605 A JP 2003134605A JP 2003134605 A JP2003134605 A JP 2003134605A JP 4201640 B2 JP4201640 B2 JP 4201640B2
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Description
【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、及び平均粒子径が２〜５μｍで球形又は不定形の熱伝導フィラー粉末からなる表示パネル用の熱伝導シートである。
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２〜５μｍ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２〜５μｍ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]
BACKGROUND OF THE INVENTION
The present invention relates to a heat conductive sheet that is interposed between heat sinks of a plasma display panel or an organic electroluminescence display and conducts heat generated in these members to the heat sink, and in particular, maintains a bonding area of the heat conductive sheet. The present invention relates to a thermal conductive sheet that improves thermal 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]
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 measure. The display panel generates heat due to internal discharge when performing light emission display, and locally expands and contracts to cause breakage and image quality deterioration. For this reason, means has been proposed for dissipating the generated heat by attaching a heat dissipation plate with a heat conductive sheet interposed on the back surface of the display panel. As the 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 coated on a film of polyester or the like, and the coating film is irradiated with ultraviolet rays to be polymerized. The sheet | seat obtained by this is known (refer patent document 1).
[0003]
In order to affix such a heat conductive sheet to a heat sink or display panel which is a rigid plate-like body, the flexible heat conductive sheet is bent and attached while expelling the bubbles, while expelling the bubbles. Since it can adhere | attach uniformly, sufficient heat conduction in the interface of a heat conductive sheet, a heat sink, etc. is realizable. However, when the laminate of the heat sink or display panel and the heat conductive sheet obtained in this way is attached to the other member, the rigid laminate cannot be bent. At the same time, there is a problem that bubbles are entrained at the interface between them and the substantial adhesion area is greatly reduced, and the entrained bubbles become a heat insulating material and the thermal conductivity is greatly reduced. It was.
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 11-292998 [Problems to be Solved by the Invention]
[0005]
The present invention, when fixing the heat sink to the back surface of the display panel, allows the bubbles entrained in these interfaces to escape, thereby maintaining a substantial adhesion area and obtaining good thermal conductivity at the interfaces. It is an object of the present invention to provide a heat conductive sheet to be manufactured.
[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 problems can be solved by providing a specific heat-sensitive adhesive surface layer on the surface of the heat conductive sheet, leading to the present invention.
[0007]
That is, the present invention relates to a heat conductive substrate obtained by molding a heat conductive composition in which a heat conductive filler is blended with an acrylic copolymer into a sheet shape, and heat is applied 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 shape, at least one of the heat-sensitive adhesive surface layers is a wax having a melting point of 40 ° C to 100 ° C and / or It is a heat conductive sheet for a display panel comprising a paraffin, a thermoplastic resin having a softening point of 40 ° C. to 100 ° C., and a spherical or irregular heat conductive filler powder having an average particle diameter of 2 to 5 μm .
Furthermore, when at least one of the heat-sensitive adhesive surface layers is 100 parts in total of the wax and / or paraffin and the thermoplastic resin, a heat conductive sheet containing 20 to 400 parts of heat conductive filler powder is preferable, and the heat It is particularly preferable that the conductive filler powder is aluminum hydroxide.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The heat conductive sheet of the present invention has a heat conductive substrate and a heat-sensitive adhesive surface layer (hereinafter simply referred to as “surface layer”) laminated on one or both surfaces of the heat conductive substrate, and the surface layer is a display panel. It is softened and flowed by the heat generated when it is put into operation, and the adhesive area was expanded by releasing the air bubbles that were trapped when fixing the heat sink to the back of the display panel, improving the thermal conductivity. It is a feature.
[0009]
The heat conductive base material of this invention consists of a heat conductive composition which mix | blended the heat conductive filler with the acrylic type copolymer. The acrylic copolymer used for the heat conductive substrate is a copolymer composed of two or more kinds of acrylic acid, methacrylic acid, and derivatives thereof, and a general one can be appropriately selected and employed. Specifically, methyl group, ethyl group, propyl group, butyl group, isooctyl group, isononyl group, isodecyl group, dodecyl group, lauryl group, tridecyl group, pentadecyl group, hexadecyl group, heptadecyl group, octadecyl group, nonadecyl group, And a copolymer composed of two or more kinds of (meth) acrylic acid ester having an alkyl group having 20 or less carbon atoms, such as an ecoxyl group.
[0010]
Some copolymer components include hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, N-methylolacrylamide, acrylonitrile, methacrylonitrile, glycidyl acrylate, vinyl acetate, styrene. , One or more of isoprene, butadiene, isobutylene, vinyl ether and the like may be used.
[0011]
Moreover, as a heat conductive filler mix | blended with a heat conductive base material, if it can give sufficient heat conductivity, a general inorganic filler can be used, It is not specifically limited. Specific examples include alumina, aluminum hydroxide, boron nitride, silicon oxide, and aluminum nitride. Among these, aluminum hydroxide is particularly preferable in terms of obtaining flame retardancy.
[0012]
These fillers are usually blended in an amount of about 50 to 300 parts per 100 parts of the resin component for the purpose of obtaining sufficient thermal conductivity. These fillers can be mixed with the resin by a general method.
[0013]
Moreover, a modifier, an anti-aging agent, a heat stabilizer, a colorant, a flame retardant, etc. may be added to the heat conducting substrate as needed, as long as the object of the present invention is not impaired.
[0014]
A heat conductive substrate can be obtained by processing the resin composition obtained by mixing these fillers with the acrylic copolymer into a sheet shape by a method such as doctor blade or 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 generally 0.5 mm to 3 mm, and the heat conductivity is 0.4 w / m · k. The above is preferable. Moreover, this heat conductive base material may consist of the multilayer structure of a different resin composition according to the intended purpose.
[0015]
The surface layer of the present invention comprises a mixture in which a spherical or amorphous heat conductive filler powder having an average particle diameter of 2 to 5 μm is dispersed in a fluidizing agent such as wax and / or paraffin having a melting point of 40 ° C. to 100 ° C. Can be used. When the melting point of 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, 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, the temperature of the heat conductive sheet rises to about 100 ° C. due to heat conduction from the display panel. When the melting point is less than 40 ° C., the surface layer flows out at that time, voids are generated, and heat conduction is deteriorated. On the other hand, when the melting point is 100 ° C. or higher, the softened state is not achieved and the voids generated during the 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 the surface layer, the temperature when the heat conductive sheet is attached to a display panel or the like is used. It is also very important that the adhesion is improved with the rise, and as a result, the thermal conductivity is improved.
[0016]
The surface layer can be formed into the above-mentioned sheet shape by a method such as doctor blade or comma roll. On the other hand, the surface layer is measured in accordance with JISK7206 (Vicat softening temperature test) in addition to the above-mentioned components in that the uniform dispersibility of the heat conductive filler in this sheet forming step is good and the film forming property is good. The mixture which added the thermoplastic resin component whose softening temperature was 40-100 degreeC was preferable. The reason why the above-mentioned range is preferable for the softening temperature of the thermoplastic resin is the same as in the case of the melting point of the wax and / or paraffin. 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, or an ethylene-α-olefin resin is used. A polymer, an ethylene-vinyl acetate copolymer and the like are preferable. The addition amount of these thermoplastic resins may be appropriately set from the viewpoint of film forming properties. However, when the total amount of organic substances composed of 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]
Further, a heat conductive filler is blended and used in the surface layer as long as the softening temperature and workability are not impaired. As a result, the thermal conductivity of the surface layer can be increased, and the thermal conduction efficiency of the entire thermal conduction sheet can be improved.
[0018]
As the heat conductive filler to be blended in the surface layer, general ones can be selected and adopted as appropriate. However, alumina, aluminum hydroxide, and boronite are excellent in terms of heat conductivity and good dispersibility with the resin. Ride, silicon oxide, aluminum nitride and the like are preferable. In particular, aluminum hydroxide is preferable in that flame retardancy is obtained. These fillers can be mixed with the organic component by a general method.
[0019]
As these heat conductive fillers, those having a spherical or irregular shape and an average particle diameter of 2 to 5 μm are used. 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. Further, the blending amount of these fillers is preferably 20 to 400 parts with respect to 100 parts of the organic component. If it is less than 20 parts, the thermal conductivity of the thermal conductive sheet may be insufficient. If it exceeds 400 parts, cracks will occur on the surface of the surface layer when the thermal conductive sheet is folded and attached to a display panel or a heat sink. On the other hand, there are cases where the adhesiveness when the surface layer is thermally bonded to the other display panel or the heat sink is insufficient, and sufficient adhesion cannot be achieved.
[0020]
Further, a modifier, an anti-aging agent, a heat stabilizer, a colorant, a flame retardant, etc. may be added to the surface layer as long as the object of the present invention is not hindered.
[0021]
The heat conductive sheet of the present invention is used by being attached to the surface of a display panel or a heat sink by a surface layer. This surface layer softens and flows due to heat generated when the display panel is in an operating state, and the display panel It plays the role of releasing the air bubbles that are trapped when the heat sink is fixed to the back of the. This is very important in the present invention.
[0022]
What is necessary is just to select the thickness of a surface layer suitably according to the magnitude | size of the display panel and heat sink to fix. However, if the thickness is too thick, the surface layer itself becomes a heat insulating layer and the thermal conductivity decreases, and if it is too thin, the entrained bubbles cannot be released and the bonding area is reduced. The thickness is preferably 10 to 300 μm, more preferably 30 to 200 μm.
[0023]
The heat conductive sheet of this invention can be manufactured, for example with the following manufacturing methods. First, a resin composition in which a heat conductive filler is blended with an acrylic copolymer is applied onto a polyester film which has been subjected to a release treatment with silicone or the like by a method such as doctor blade or comma roll. Thus, a heat conductive substrate is formed by forming into a sheet shape, and the heat-sensitive adhesive surface layer is formed into a sheet shape and laminated on one or both surfaces of the heat conductive substrate to obtain a heat conductive sheet. It is done.
[0024]
In addition, when using the heat conductive sheet of the present invention having a surface layer on only one surface of the heat conductive substrate, the tacking force of the heat conductive sheet is used for the member to be initially attached to the display panel or the heat sink. It is desirable to attach a surface that does not have a surface layer. That is, at the time of pasting, the flexible heat conductive sheet is bent as described above and adhered while expelling the bubbles, so that the bubbles can be uniformly adhered while expelling the bubbles. Sufficient heat conduction at the interface with a plate or the like can be realized. The display panel or the heat dissipation plate and the heat conductive sheet obtained in this way are laminated to the surface of another member (display panel or heat dissipation plate) and the surface layer side does not cause a problem with the display panel. Thus, the laminate of the display panel and the heat radiating plate having good thermal conductivity as described above can be obtained.
[0025]
In the case of the heat conductive sheet having the surface layer on both surfaces of the heat conductive base material, the display panel, the heat conductive sheet and the heat radiating plate are sequentially stacked, and are pressed and bonded at an appropriate pressure to obtain good heat. A laminate of conductive display panel and heat sink can be obtained.
[0026]
【Example】
The present invention will be described more specifically with reference to examples.
(Evaluation methods)
The characteristic evaluation of the present invention was performed by the following evaluation method. In addition, these evaluation methods show an example of the method for showing the effect of this invention.
[0027]
1. Evaluation of adhesion ratio For the heat conductive sheet with a surface layer on one side, the surface of the heat conductive sheet on the side without the surface layer is affixed to the aluminum plate while bending it so that air does not enter, and reciprocated once with a 2 kg roller. After the pressure bonding, a glass plate having a length of 210 mm, a width of 300 mm, and a thickness of 5 mm was gently placed on the surface layer of the heat conductive sheet and cured at 80 ° C. for 72 hours to obtain a test piece. Moreover, also about the heat conductive sheet which provided the surface layer on both surfaces, the test piece was created similarly except having stuck one surface of the surface layer to the aluminum plate. Next, the glass and heat conductive sheet bonding surfaces of these test pieces were preheated at 70 ° C. for 1 hour to soften the surface layer, and after expanding the adhesion area, the adhesion area was photographed with a digital camera through the glass. The adhesion ratio was calculated from the number of image dots obtained by image processing.
[0028]
2. Thermal conductivity In the present invention, the thermal conductivity of the sheet is first screwed so that a pressure of 0.34 MPa is applied between the TO-3 type copper heater case and the copper plate, and then the heater case and the copper plate. After heating to 55 ° C and further cooling them to room temperature, after confirming that the temperature difference between the heater case and the copper plate is 0.1 ° C or less, apply power 15W to the heater case for 4 minutes. The temperature difference between the copper heater case and the copper plate at the time of holding was measured and calculated by the following formula (1).
[0029]
[Formula 1]
Based on the value of the obtained thermal resistance, the thermal conductivity was calculated by the following formula (2). Here, the thickness of the sample is the thickness at the time of measuring the thermal resistance (after screwing the sample so as to apply a pressure of 0.34 MPa, the heater case and the copper plate were heated to 55 ° C., and further cooled to room temperature. Time sample thickness). The heat transfer area is a TO-3 type heat transfer area of 0.0006 m 2 .
[0031]
[Formula 2]
3. Evaluation of bendability The state of cracks in the surface layer generated when the heat conductive sheet is attached to the display panel and the heat sink was visually evaluated according to the following criteria. When cracks occur, unevenness occurs when sticking to a display panel or heat sink, resulting in an increase in thermal resistance.
○: No cracking occurs 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 The adhesiveness of the surface layer when the heat conductive sheet is attached to the display panel and the heat sink was measured by measuring the peak value of the tack value using an NS probe tack tester manufactured by Nichiban Co., Ltd., and evaluated according to the following criteria: . If the tack force is very small, the heat conductive sheet cannot be fixed to the display panel or heat sink.
○: The peak value of the probe tack tester is 0.5 N / 20 mm 2 or more.
X: The peak value of the probe tack tester is 0.5 N / 20 mm 2 or less.
5. Evaluation of Adhesion State The heat conduction sheet of the display panel and the adhesiveness were determined according to the following criteria as to whether or not the surface layer softened during heating and flowed out from the adhesion part. When it flows out, the adhesion area decreases and the thermal resistance increases.
○: The bonded portion flows by heating, and the surface layer does not flow out from the bonded portion with time, and the bonded area does not decrease.
(Triangle | delta): Although an adhesion part does not flow by heating, an adhesion area is not improved so much.
X: The bonded portion flows by heating, and the surface layer flows out from the bonded portion with the passage of time, and the bonded area decreases.
[0033]
(Example 1)
Aluminum hydroxide (Showa Denko Co., Ltd.) is used as a heat conductive filler for 100 parts of the resin component of an emulsion in which an acrylic copolymer is dispersed in water (Pegard 851 manufactured by High Pressure Gas Industry Co., Ltd .; resin component 55%). H-32) is mixed with a heat conductive composition containing 135 parts, and then coated into a sheet by a method such as a doctor blade or comma roll, and then further dried to obtain a 900 μm sheet-like heat. A conductive substrate was obtained. Next, 100 parts of ethylene-vinyl acetate copolymer resin “Evaflex EV150 made by Mitsui DuPont Polychemical Co., Ltd.” and “paraffin wax 115 (melting point 47 ° C.)” made by Nippon Seiwa Co., Ltd. were used as the heat-sensitive adhesive surface layer. -40 parts of vinyl acetate copolymer resin were mixed in 400 parts of toluene solvent (relative to ethylene-vinyl acetate copolymer resin) until uniform. 50 parts of aluminum hydroxide “H-32 manufactured by Showa Denko KK”, which is 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 onto the polyester film subjected to the silicone release treatment by a doctor blade method to form a surface layer having a thickness of 100 μm, and one side of the heat conductive substrate. A heat conductive sheet was laminated by a dry lamination method. The evaluation was performed using this sheet, and the results are shown in Table 1.
[0034]
[Table 1]
(Example 2)
Except that a heat-sensitive adhesive surface layer having a thickness of 50 μm was formed on both surfaces of a heat-conductive substrate having a thickness of 900 μm, a heat-conductive sheet was prepared and evaluated in the same manner as in Example 1, and the results are shown in Table 1. Indicated.
[0036]
(Example 3)
Except for mixing 350 parts of aluminum hydroxide “H-32” manufactured by Showa Denko Co., Ltd., which is a heat conductive filler of a heat-sensitive adhesive surface layer laminated on one side of a 900 μm thick heat conductive base material, the same as in Example 1. A heat conductive sheet was prepared and evaluated in the same manner, and the results are shown in Table 1.
[0037]
(Comparative Example 1)
Aluminum hydroxide (Showa Denko Co., Ltd.) is used as a heat conductive filler for 100 parts of the resin component of an emulsion in which an acrylic copolymer is dispersed in water (Pegard 851 manufactured by High Pressure Gas Industry Co., Ltd .; resin component 55%). The heat conductive composition which mix | blended 135 parts of manufactured H-32) was shape | molded and dried, and the 1000-micrometer-sheet-like heat conductive sheet was obtained. 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 except that the ethylene-vinyl acetate copolymer resin of the heat-sensitive adhesive surface layer was changed to "Resin having a vinyl acetate content of 22% and a softening temperature of 30 ° C by Evaflex MFR150 manufactured by Mitsui DuPont Polychemical 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. During use in a heated state, the surface layer liquefied and flowed out, and the desired adhesion ratio and thermal conductivity could not be obtained.
[0039]
(Comparative Example 3)
Aluminum hydroxide “H-32 manufactured by Showa Denko KK”, which is a heat conductive filler of a heat-sensitive adhesive surface layer laminated on one side of a 900 μm thick heat conductive substrate, except that the average particle size was 0.5 μm, 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 increased so much that the interface between the heat conductive sheet and the glass plate was peeled off, and the intended heat conductivity and tackiness could not be obtained.
[0040]
【The invention's effect】
The heat conductive sheet of the present invention can effectively release bubbles entrained in the interface when fixing the heat radiating plate to the back surface of the display panel, expanding the adhesion area and maintaining the adhesion area. A heat conductive sheet with improved heat conductivity can be provided.
Claims (3)
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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 true JP4201640B2 (en) | 2008-12-24 |
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| JP2007246664A (en) * | 2006-03-15 | 2007-09-27 | Polymatech Co Ltd | Heat conductive sheet |
| JP5042899B2 (en) * | 2008-03-31 | 2012-10-03 | ポリマテック株式会社 | Thermally conductive sheet and method for producing the same |
| JP2013062379A (en) * | 2011-09-13 | 2013-04-04 | Nitto Denko Corp | Thermally conductive sheet and method for manufacturing the same |
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