JP5070554B2 - ITO powder, transparent conductive film and method for forming the same - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明はＳｎ含有Ｉｎ酸化物（ＩＴＯという。）粉とこれを用いた透明導電性膜に関するものである。
【０００２】
【従来の技術】
比較的少量のＳｎを含有するＩｎ酸化物すなわちＩＴＯは、可視光に対する高い透光性と導電性を示すことから各種表示デバイスや太陽電池などの透明導電性膜として用いられている。
このＩＴＯを用いた透明導電性膜の成膜方法としては、スパッタリング法などの物理的方法、粒子分散液または有機化合物を塗布する塗布法が知られている。この塗布法による塗膜は、スパッタリング法などの物理的方法による膜に比べて導電性が多少低いものの、真空装置等の高価な装置を用いることなく大面積や複雑形状の成膜が可能であり低コストとなる利点がある。さらにこの塗布法の中でも粒子分散液による方法は塗布膜を熱分解させる必要のある有機化合物塗布法に比べ比較的低温のプロセスで成膜でき、良好な導電性も得られることからブラウン管の電磁波シールド膜として広く用いられており、ＬＣＤやＥＬなどの表示デバイスの透明電極への用途も検討されている。
【０００３】
一方、このように成膜されるＩＴＯ導電性塗膜においては、従来、塗料として一般に粒状ＩＴＯ粉が用いられていたが、近年、さらに膜抵抗の低減および導電経路の形成のため粒子同士の接触度を高めるべく針状、板状、あるいはフレーク状のＩＴＯ粉が提案されるようになった。このような種々の粉体粒子形状を得る試みとしては、
（Ａ）混合原料液を加熱濃縮した後の高粘度スラリーから長軸長５μm 以上、長軸／短軸の軸比５以上の針状ＩＴＯ粒子を得る方法（特開平７−２３２９２０、特開平７−２３５２１４）、
（Ｂ）長さ１〜１００μm 、幅０．２〜２０μm 、厚み０．０１〜２μmの短冊状酸化チタン粒子にＳｎ含有Ｉｎ酸化物等の導電層を被覆する方法（特開平８−２１７４４６）、
（Ｃ）ＳｎとＩｎとを含む酸性液のアルカリ水溶液による二段中和処理により長軸長０．２〜０．９５μm 、短軸長０．０２〜０．１μm 、軸比４以上の針状ＩＴＯ粒子を得る方法（特開平６−８０４２２）などの製法が知られている。
【０００４】
【発明が解決しようとする課題】
しかしながら、従来の塗膜の成膜方法に関し、前記のように利点の多い粒子分散法による塗膜にあっても、スパッタリング膜等に比べてもまだ導電性が低く、ブラウン管の大型化や表示デバイスの高精細電極用にはいまだ対応しきれないという問題があり、透光性を保ちかつ導電性が向上し、前記高精細電極の用途にも対応できる塗膜の形成を可能とするＩＴＯ粉の開発が望まれている。
【０００５】
また、粉体の粒子形状の面から導電性の向上を求める従来の方法に関する前記（Ａ）の方法については、得られるＩＴＯ粒子が大きく、膜抵抗は低減されるものの、透過率等の光学特性が悪く、特に散乱光が多く発生し塗膜のヘイズが大きくなるという問題がある。前記（Ｂ）の方法については、粒子が短冊状であり良好な接触性が得られると考えられるが、粒子が大きく、前記（Ａ）の方法と同様の問題があり、さらに、導電性が低い酸化チタン粒子を導電性材料で被覆するので粒子内電気抵抗が高く塗膜において十分な導電性が得られないという問題がある。また、前記（Ｃ）の方法については、前記（Ａ）よりも微粒子であり光学特性は多少改善されるが、可視光の波長（４００〜７００nm）の１／２のサイズより大きく、塗膜中にＩＴＯ粒子が充填された場合に散乱光が発生し、可視光の十分な光透過率が得られず、ヘイズ防止を図ることができないという問題がある。すなわち、針状ＩＴＯ粒子の使用によれば、膜抵抗においては改善されるものの、散乱光に係る光学特性については十分でなく、さらに微粒化を必要とするのではないかという課題が残っていた。なお、ヘイズは光の散乱現象に係る散乱度（％）に関する特性であって、透明電極膜の特性としては小さい程好ましく、本発明者等によりこのヘイズはＩＴＯ粉体粒子の形状や分散度により強い影響を受けることが明らかになった。
【０００６】
本発明者等はこのため、ＩＴＯ粉体粒子についてその大きさ、さらには軸比を規定した針状または板状の形状とすることにより、塗膜において導電材としてのＳｎ含有Ｉｎ酸化物粉体粒子同士の接触面を多くして導電性を向上させ、また散乱光を抑制することが可能と考え、ＳｎとＩｎとを含有する酸性水溶液にアルカリを添加する中和処理を２段階以上の工程で行うことにより、凝集のない微細なＳｎ含有Ｉｎ酸化物粒子を作成することに成功し、従来に増して導電性を向上させると共にある程度前記散乱光を抑制させることができた。
しかしながら、このように針状ＩＴＯ粉体粒子を微細化することにより膜抵抗の改善と高い透光率の維持を可能にしたが、粒状粒子に比較すると、ヘイズの抑制力、分散性の点からポットライフとも十分ではない、すなわち、分散安定性とくに貯蔵安定性において粒子凝集、沈降により塗膜にした場合に透光率が十分ではなく、さらに改善が望まれている。
【０００７】
このような状況に鑑み、本発明は、良好な分散性を有して粒子分散スラリーの塗布を良好に行うことができ、優れた光学特性すなわち高い透光性と低いヘイズを示すと共に高い導電性を示す塗膜を形成できる最適なＩＴＯ粉と該ＩＴＯ粉による透明導電性膜の提供を目的とするものである。
【０００８】
【課題を解決するための手段】
前記の目的を達成するため、本発明者等は微細なＩＴＯ粒子の形状に注目し、２種以上の形状のＩＴＯ粒子を組み合わせることによって高導電率、高透過率を達成できる可能性を見出し検討を行うことにより本発明に至った。
すなわち、本発明は第１に、少なくとも針状ＩＴＯ粒子と粒状ＩＴＯ粒子とを含み、前記針状ＩＴＯ粒子と前記粒状ＩＴＯ粒子との重量比が２：９８〜９８：２であり、前記針状ＩＴＯ粒子は長軸長が０．５μｍ以下、短軸長が０．１μｍ以下、軸比が１．５〜１０でかつＳｎＯ2含有量が２〜２０ｗｔ％であり、前記粒状ＩＴＯ粒子は粒径が０．０５μｍ以下でかつＳｎＯ2含有量が２〜２０ｗｔ％である透明導電性膜用ＩＴＯ粉を、第２に、少なくとも針状ＩＴＯ粒子と粒状ＩＴＯ粒子とを含み、前記針状ＩＴＯ粒子と前記粒状ＩＴＯ粒子との重量比が２０：８０〜８０：２０であり、前記針状ＩＴＯ粒子は長軸長が０．５μｍ以下、短軸長が０．１μｍ以下、軸比が１．５〜１０でかつＳｎＯ2含有量が２〜２０ｗｔ％であり、前記粒状ＩＴＯ粒子は粒径が０．０５μｍ以下でかつＳｎＯ2含有量が２〜２０ｗｔ％である透明導電性膜用ＩＴＯ粉を、第３に、針状ＩＴＯ粒子と粒状ＩＴＯ粒子とからなり、前記針状ＩＴＯ粒子と前記粒状ＩＴＯ粒子との重量比が２：９８〜９８：２であって、前記針状ＩＴＯ粒子は長軸長が０．５μｍ以下、短軸長が０．１μｍ以下、軸比が１．５〜１０でかつＳｎＯ2含有量が２〜２０ｗｔ％であり、前記粒状ＩＴＯ粒子は粒径が０．０５μｍ以下でかつＳｎＯ2含有量が２〜２０ｗｔ％である透明導電性膜用ＩＴＯ粉を、第４に、針状ＩＴＯ粒子と粒状ＩＴＯ粒子とからなり、前記針状ＩＴＯ粒子と前記粒状ＩＴＯ粒子との重量比が２０：８０〜８０：２０であって、前記針状ＩＴＯ粒子は長軸長が０．５μｍ以下、短軸長が０．１μｍ以下、軸比が１．５〜１０でかつＳｎＯ2含有量が２〜２０ｗｔ％であり、前記粒状ＩＴＯ粒子は粒径が０．０５μｍ以下でかつＳｎＯ2含有量が２〜２０ｗｔ％である透明導電性膜用ＩＴＯ粉を、第５に、少なくとも針状ＩＴＯ粒子と粒状ＩＴＯ粒子とを含むＩＴＯ粉からなり、前記針状ＩＴＯ粒子と前記粒状ＩＴＯ粒子との重量比が２：９８〜９８：２であって、前記針状ＩＴＯ粒子は長軸長が０．５μｍ以下、短軸長が０．１μｍ以下、軸比が１．５〜１０でかつＳｎＯ2含有量が２〜２０ｗｔ％であり、前記粒状ＩＴＯ粒子は粒径が０．０５μｍ以下でかつＳｎＯ2含有量が２〜２０ｗｔ％であり、膜抵抗が１０ｋΩ／□以下であって、ヘイズ測定において透過率が８０％以上でかつヘイズ値が２％以下である透明導電性膜を、第６に、少なくとも針状ＩＴＯ粒子と粒状ＩＴＯ粒子とを含むＩＴＯ粉からなり、前記針状ＩＴＯ粒子と前記粒状ＩＴＯ粒子との重量比が２０：８０〜８０：２０であって、前記針状ＩＴＯ粒子は長軸長が０．５μｍ以下、短軸長が０．１μｍ以下、軸比が１．５〜１０でかつＳｎＯ2含有量が２〜２０ｗｔ％であり、前記粒状ＩＴＯ粒子は粒径が０．０５μｍ以下でかつＳｎＯ2含有量が２〜２０ｗｔ％であり、膜抵抗が１０ｋΩ／□以下であって、ヘイズ測定において透過率が８０％以上でかつヘイズ値が２％以下である透明導電性膜を、第７に、針状ＩＴＯ粒子と粒状ＩＴＯ粒子とからなるＩＴＯ粉からなり、前記針状ＩＴＯ粒子と前記粒状ＩＴＯ粒子との重量比が２：９８〜９８：２であって、前記針状ＩＴＯ粒子は長軸長が０．５μｍ以下、短軸長が０．１μｍ以下、軸比が１．５〜１０でかつＳｎＯ2含有量が２〜２０ｗｔ％であり、前記粒状ＩＴＯ粒子は粒径が０．０５μｍ以下でかつＳｎＯ2含有量が２〜２０ｗｔ％であり、膜抵抗が１０ｋΩ／□以下であって、ヘイズ測定において透過率が８０％以上でかつヘイズ値が２％以下である透明導電性膜を、第８に、針状ＩＴＯ粒子と粒状ＩＴＯ粒子とからなるＩＴＯ粉からなり、前記針状ＩＴＯ粒子と前記粒状ＩＴＯ粒子との重量比が２０：８０〜８０：２０であって、前記針状ＩＴＯ粒子は長軸長が０．５μｍ以下、短軸長が０．１μｍ以下、軸比が１．５〜１０でかつＳｎＯ2含有量が２〜２０ｗｔ％であり、前記粒状ＩＴＯ粒子は粒径が０．０５μｍ以下でかつＳｎＯ2含有量が２〜２０ｗｔ％であり、膜抵抗が１０ｋΩ／□以下であって、ヘイズ測定において透過率が８０％以上でかつヘイズ値が２％以下である透明導電性膜を、第９に、前記針状ＩＴＯ粒子と前記粒状ＩＴＯ粒子とを溶剤中で混合して分散させたスラリーを透明板に塗布することを特徴とする前記第５〜第８のいずれかに記載の透明導電性膜の成膜方法を提供するものである。
【０００９】
【発明の実施の形態】
本発明における透明導電性膜用ＩＴＯ粉は、基本的に、針状ＩＴＯ粒子と粒状ＩＴＯ粒子とが混在しているＩＴＯ粉であり、針状ＩＴＯ粒子による良好な膜抵抗と粒状ＩＴＯ粒子による高分散性を両立させることができる。すなわち、粒状ＩＴＯ粒子の存在により微細粉体粒子の分散性を向上させることによって、微細化された針状ＩＴＯ粒子による高い膜導電性を維持しながら、散乱光の発生を抑制して高光学特性すなわちヘイズ防止と高い透光性を得ることができる。また、粉体粒子の分散性が良好になったため、塗布法の利点が十分に生かされるものとなる。さらにまた、これらの効果は特定形状で特定粒度のＩＴＯ粉を使用することによりより確実なものになる。なお、本発明における針状ＩＴＯ粒子は実質的に板状またはフレーク状のＩＴＯ粒子を含むものであり、また、粒状ＩＴＯ粒子は実質的に球状のＩＴＯ粒子を含むものである。
【００１０】
前記混合ＩＴＯ粉における針状ＩＴＯ粒子は、ＳｎＯ2含有量が２〜２０ｗｔ％であり、長軸長が０．５μm以下、好ましくは０．２μm以下で、短軸長が０．１μm 以下の針状または板状の形状を有する微細なＳｎ含有Ｉｎ酸化物粒子であり、さらに、前記長軸長／前記短軸長の軸比が１．５〜１０のものである。
この針状ＩＴＯ粒子の長軸長は、０．５μmを超えると可視光の散乱が発生し、透光性、ヘイズ等の光学特性が低下する。特に、長軸長が０．２μm以下では可視光の散乱が一層抑制される。また、短軸長は、０．１μm を超えると粒子同士の接触面が低く、膜導電性が低くなり、逆に、０．０５μm 以下では膜導電性が一層向上する。さらに、長軸長／短軸長の軸比が１．５〜１０の範囲を外れると導電性、分散性、粒子内結晶性が低下し、特に１．５未満では形状異方性の効果、抵抗値の低下の効果が得られない。
【００１１】
本発明者等が見出したこのような微細ＩＴＯ粉における微細針状ＩＴＯ粒子の製造は、例えば次の各工程によって行うことができる。
（１）原料酸性水溶液の調製
ＩｎをＨＣｌで溶解した塩化インジウム水溶液にさらに塩化第二錫を溶解して出発溶液である酸性水溶液を調製する。液中のＩｎ濃度は２〜５０ｇ／ｌとする。また、最終のＩＴＯ中のＳｎ含有量はＳｎＯ2換算で２〜２０ｗｔ％とする。２〜２０ｗｔ％の範囲を外れると酸化物の導電性が低下する。使用する酸としてはＨＣｌに限らず、ＨＮＯ3 、Ｈ2ＳＯ4 等も用いることができる。また、予備中和処理と中和処理におけるアルカリとしてはＮＨ3 、ＮＨ4ＯＨ、ＮａＯＨ、またはＫＯＨ等が用いられる。
【００１２】
（２）予備中和および中和
まず前記酸性水溶液の液温が４５℃以下において、前記アルカリを添加して、ｐＨ２〜４に予備中和する。さらに、その後の中和にあたっては、３０分〜２時間で昇温し液温を５０℃以上に昇温して前記アルカリを添加し、ｐＨ７〜８に中和して前駆体としてのＳｎ含有Ｉｎ水酸化物を沈殿させ、これを濾過、洗浄、乾燥する。
すなわち、ＳｎとＩｎとを含有する酸性水溶液を、まず予備中和処理により微粒子核を生成させ、次いでより高温の中和過程でその外殻に水酸化物を成長させることにより、微細な針状または板状の水酸化物粉体粒子を生成させることができる。
【００１３】
（３）焼成
得られた前記Ｓｎ含有Ｉｎ水酸化物を焼成し、脱水分解、焼結を行う。
焼成雰囲気は水蒸気を含有する窒素等の不活性ガス雰囲気とし、好ましくはＮＨ3等の還元性ガスも含有させる。焼成温度は３００〜１０００℃とする。前記の温度、雰囲気での焼成によって水酸化物粉体粒子の形状異方性を維持して目的の微細な針状ないし板状のＩＴＯ粉を得ることができる。
【００１４】
本発明の微細混合ＩＴＯ粉において用いる粒状ＩＴＯ粒子の製造は、従来技術に属するものであるが、例えば、次のようにして行うことができる。
Ｉｎを含有する塩酸水溶液に塩化第二錫を添加した酸性水溶液およびＮＨ4ＯＨ等によるアルカリ水溶液を調製し、前記酸性水溶液に前記アルカリ水溶液を添加して中和させてｐＨ７〜８程度とし、これを濾過、脱水、乾燥して、Ｓｎ含有Ｉｎ水酸化物を得る。この水酸化物を水蒸気とＮＨ3を含有する窒素ガス雰囲気中で６００〜７００℃程度の温度で焼成することにより、長軸長／短軸長の軸比が１〜２程度の粒状ないし球状のＩＴＯ粒子を得ることができる。
【００１５】
得られた前記針状ＩＴＯ粒子の粉と前記粒状ＩＴＯ粒子の粉を任意の割合で混合する。すなわち、両ＩＴＯ粉を溶媒中に均一に分散させて混合することにより塗料スラリー化することができる。得られたスラリーをガラス等透明板に塗布し、溶媒を揮発させて膜を固定することにより、高い分散性を有し、ヘイズが少なく透光性が高く、低抵抗の透明導電性塗膜を得ることができる。
また溶媒との混合については、前記針状ＩＴＯ粒子の粉と前記粒状ＩＴＯ粒子の粉を任意の割合で溶媒中に装入して混合、分散することもできるし、予め前記針状ＩＴＯ粒子の粉と前記粒状ＩＴＯ粒子の粉とを任意の割合で乾式混合しておいてから溶媒中に装入して分散することもできる。さらに、前記針状ＩＴＯ粒子と前記粒状ＩＴＯ粒子とが混在した粉を製造して溶媒に装入して分散することもできる。
針状ＩＴＯ粒子と粒状ＩＴＯ粒子とが混在した粉を製造するには、針状Ｓｎ含有Ｉｎ水酸化物スラリーと粒状Ｓｎ含有Ｉｎ水酸化物スラリーとを混合し、濾過、脱水、乾燥、焼成して製造することができる。また、針状Ｓｎ含有Ｉｎ水酸化物粒子と粒状Ｓｎ含有Ｉｎ水酸化物粒子とをあらかじめ混合しスラリー化した後、濾過、脱水、乾燥、焼成して製造することもできる。
塗料化の方法には従来の方法を使用することができ、溶媒としてアルコール、ケトン、エーテル等の有機溶媒、分散剤として界面活性剤、カップリング剤等を添加し、ビーズミル等の分散装置を用いて分散させる。また、バインダーとなる有機系または無機系の結合剤を添加するか、ＩＴＯ塗料による成膜後にその塗膜上にバインダーを成膜して固定してもよい。
【００１６】
膜抵抗値とヘイズ防止とを効果的に両立させるための針状ＩＴＯ粒子と粒状ＩＴＯ粒子との混在比は、重量比で２：９８〜９８：２の広範囲において有効であるが、好ましくは５：９５〜５０：５０、さらに好ましくは５：９５〜３０：７０である。
前記のように、針状ＩＴＯ粒子の長軸長は０．５μm 以下、短軸長は０．１μm以下で、軸比は１．５〜１０で、ＳｎＯ2含有量は２〜２０ｗｔ％が好ましい。前記粒状ＩＴＯ粒子は、粒径が０．０５μm以下でＳｎＯ2含有量は２〜２０ｗｔ％が好ましい。
このような透明導電性膜とすることにより、膜抵抗が１０ｋΩ／□以下であり、ヘイズ測定において透過率が８０％以上、ヘイズ値が２％以下の優れた光学特性を得ることができる。
なお粉体の混合方法は、乾式と湿式とのどちらによっても効果を得ることができる。粉体で乾式混合した方が一度の分散操作ですみ生産性が向上するメリットはあるが、設備や操作難易度等をも配慮して選択される。
【００１７】
【実施例】
以下に実施例および比較例により本発明をさらに説明するが、本発明の技術的範囲はこれら実施例に限定されるものではない。
【００１８】
〔実施例１〕
Ｉｎを１８ｗｔ％含むＨＣｌ溶液２００ｇを純水で２．９L とし、さらに塩化第二錫を５．４ｇ添加して混合溶液として出発溶液の酸性水溶液を調製した。また２５％アンモニア水１５０ｇを純水１３５０g で希釈してアルカリ溶液を調製した。次いで、液温２０℃の酸性水溶液にアルカリ溶液の一部を１７分間添加してｐＨ３となるように予備中和した。さらに、予備中和液の液温を９０℃まで昇温し、残りのアルカリ溶液を６０分間かけて添加した。最終のｐＨは７．５であった。これを濾過、脱水、乾燥して針状粉体粒子からなるＳｎ含有Ｉｎ水酸化物の沈殿を得た。
次いで、このＳｎ含有Ｉｎ水酸化物を管状炉に入れ、１．５ｖｏｌ％の水蒸気と０．０５ｖｏｌ％のＮＨ3ガスとを含有する窒素ガスの雰囲気中にて６００℃で２時間焼成した。こうして得られたＳｎ含有Ｉｎ酸化物粒子すなわちＳｎ含有率が５ｗｔ％のＩＴＯ粉体粒子は平均長軸長が０．０６９μm、平均短軸長が０．０２９μm、平均軸比が２．３８で、ＢＥＴ比表面積が３０．４ｍ２／ｇ、結晶子径Ｄｘが２０．６ｎｍの針状粉体粒子であった。
【００１９】
次に、粒状ＩＴＯ粉を製造した。
上記の針状粒子の場合と同様にして、酸性水溶液とアルカリ溶液を調製した。液温３５℃の酸性水溶液に６０分間かけてアルカリ溶液の全量を添加し、最終のｐＨを７．５とした。この中和液を濾過し、濾過物を脱水、乾燥して粒状のＳｎ含有Ｉｎ水酸化物を得た。得られたＳｎ含有Ｉｎ水酸化物粉体粒子は長軸長が０．０３９μm 、短軸長が０．０３２μmの凝集体となっていた。
次いで、このＳｎ含有Ｉｎ水酸化物を管状炉に入れ、１．５ｖｏｌ％の水蒸気と０．０５ｖｏｌ％ＮＨ3とを含有する窒素ガスの雰囲気中で６４５℃で２時間焼成した。得られたＳｎ含有Ｉｎ酸化物粉体粒子すなわちＳｎ含有率５ｗｔ％のＩＴＯ粉体粒子は粒状形状であった。この粉体粒子のＢＥＴ比表面積は２８m2／gで結晶子径Ｄｘは２６０ｎｍであった。
【００２０】
前記のようにして得られた両ＩＴＯ粉について、針状粉１ｇと粒状粉４ｇの比率で、ミキサーで混合した。
混合粉５ｇと混合溶剤２０ｇ（エタノール：プロパノール＝７：３）および分散剤としてアニオン系界面活性剤０．２５ｇを遊星ボールミル（フリッチェ製Ｐ−５型、容器容量８０ｍｌ、ＰＳＺ０．３ｍｍボール）に入れ、回転数３００ｒｐｍで３０分間回転させた。
この分散液にコロイダルシリカとエタノールを加えて、混合ＩＴＯ粉の含有量が２ｗｔ％、シリカ含有量が２ｗｔ％、残部がエタノールおよびプロパノールであるスラリーを調製し、ガラス板にスピンコートした後、２００℃で３０分間乾燥し、膜厚０．３μm の透明導電性塗膜を得た。
得られた塗膜の膜抵抗を測定したところ５．３kΩ／□であった。また、ヘイズメーターとして日本電色工業（株）製濁度計ＮＤＨ２０００を用いＪＩＳ Ｋ７１３６の方法に準拠して透過率とヘイズを測定したところ、透過率は９０％、ヘイズ値は１％で良好な透明導電性塗膜であった。
【００２１】
〔実施例２〕
実施例１で得られた針状ＩＴＯ粉２．５ｇと粒状ＩＴＯ粉２．５ｇをミキサーにて混合して混合比５０：５０とした混合ＩＴＯ粉を得て、引き続き実施例１と同様の処理によりスラリーを調製し、ガラス板上にスピンコートし乾燥して透明導電性塗膜を得た。
得られた塗膜の膜抵抗は５．２kΩ／□であり、透過率は９０％であり、またヘイズ値は１．５％であった。
【００２２】
〔実施例３〕
実施例１で得られた針状ＩＴＯ粉と粒状ＩＴＯ粉とを４ｇと１ｇの比率で混合した以外は、実施例１と同様の処理により透明導電性塗膜を得た。
得られた塗膜の膜抵抗は５．１kΩ／□であり、透過率は９０％であり、またヘイズ値は２％であった。
【００２３】
[実施例４]
実施例１におけるアルカリ予備中和の時間を１７分間から１３分間に変更した以外は実施例１と同様に行った。得られたＳｎ含有Ｉｎ酸化物針状粒子すなわちＳｎ含有率が５ｗｔ％のＩＴＯ粉体粒子は平均長軸長が０．３０９μｍ、平均短軸長が０．０７１μｍ、平均軸比が４．３７で、ＢＥＴ比表面積は２０．７m2／gで結晶子径Ｄｘは１６．７ｎｍであった。引き続き、実施例１と同様の処理により透明導電性塗膜を得た。得られた塗膜の膜抵抗は５．１kΩ／□であり、透過率は９０％であり、またヘイズ値は１．１％であった。
【００２４】
〔比較例１〕
実施例１で得られた粒状ＩＴＯ粉のみを使用して、実施例１と同様の処理により透明導電性塗膜を得た。
得られた塗膜の膜抵抗は２０kΩ／□と高く、透過率は９０％で、ヘイズ値は１％であった。
【００２５】
〔比較例２〕
実施例１で得られた針状ＩＴＯ粉のみを使用して、実施例１と同様の処理により透明導電性塗膜を得た。
得られた塗膜の膜抵抗は５kΩ／□であり、透過率は９０％であり、ヘイズ値は５％と高くなった。
【００２６】
上記実施例１〜比較例２の塗膜に関し表１にまとめて示した。
この結果から明らかなように、針状粉の混合比率が０である場合（粒状粉のみの場合）は、粉体の分散性がよく透過率も高くヘイズも抑制されているが、塗膜の膜抵抗は異常に高い状態にある。針状粉の混合比率が高くなるにつれ、分散性が抑制されてヘイズ値は若干ながら大きくなる傾向を示すが膜抵抗は低下する。針状粉の混合比が１００％の場合（粒状粉が０の場合）は膜抵抗はさらに低下するがヘイズが異常に高い状態となる。そして、針状粉と粒状粉との混合比率が少なくとも２０：８０〜８０：２０の範囲内で粉体の分散性も良好で、塗膜の抵抗性とヘイズとの両立を図ることができる。
【００２７】
【表１】
【発明の効果】
本発明によれば、針状ＩＴＯ粒子と粒状ＩＴＯ粒子とからなるＩＴＯ粉、好ましくは、長軸長および短軸長が所定値以下、軸比が所定範囲の微細な針状または板状の形状を有するＩＴＯ粉と粒径が所定値以下の粒状または球状のＩＴＯ粉を所定の比率で混合したＩＴＯ粉のスラリーによって形成される導電性塗膜は導電材粉体粒子の分散性も良好で粉体粒子同士の接触面が増加して導電性が向上し、また、粉体粒子の分散性が良好になることから散乱光が抑制されてヘイズが低く、透光性も高く、ブラウン管の大型化および表示デバイスの高精細電極用に塗布方式で対応することができ低コスト化を実現できるという顕著な効果を奏する。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to Sn-containing In oxide (ITO) powder and a transparent conductive film using the same.
[0002]
[Prior art]
In oxides containing a relatively small amount of Sn, that is, ITO, are used as transparent conductive films for various display devices, solar cells, and the like because they exhibit high translucency and conductivity with respect to visible light.
As a method for forming a transparent conductive film using ITO, a physical method such as a sputtering method and a coating method in which a particle dispersion or an organic compound is applied are known. A coating film formed by this coating method has a slightly lower conductivity than a film formed by a physical method such as a sputtering method, but can be formed in a large area or a complicated shape without using an expensive device such as a vacuum device. There is an advantage of low cost. Furthermore, among these coating methods, the particle dispersion method can be formed by a process at a relatively low temperature compared to the organic compound coating method in which the coating film needs to be thermally decomposed, and can provide good conductivity. It is widely used as a film, and its use for transparent electrodes of display devices such as LCDs and ELs is also being studied.
[0003]
On the other hand, in the ITO conductive film formed in this way, granular ITO powder has been generally used as a paint, but in recent years, contact between particles has been further reduced in order to further reduce film resistance and form a conductive path. Needle-like, plate-like, or flake-like ITO powder has been proposed to increase the degree. As an attempt to obtain such various powder particle shapes,
(A) A method of obtaining acicular ITO particles having a major axis length of 5 μm or more and a major axis / minor axis ratio of 5 or more from a high viscosity slurry after the mixed raw material liquid is heated and concentrated (JP-A-7-232920, JP-A-7 -235214),
(B) A method of coating a strip-shaped titanium oxide particle having a length of 1 to 100 μm, a width of 0.2 to 20 μm and a thickness of 0.01 to 2 μm with a conductive layer such as an Sn-containing In oxide (JP-A-8-217446),
(C) Needle shape having a major axis length of 0.2 to 0.95 μm, a minor axis length of 0.02 to 0.1 μm, and an axial ratio of 4 or more by two-step neutralization treatment with an alkaline aqueous solution of an acidic liquid containing Sn and In. Manufacturing methods such as a method for obtaining ITO particles (Japanese Patent Laid-Open No. 6-80422) are known.
[0004]
[Problems to be solved by the invention]
However, regarding the conventional method for forming a coating film, even if it is a coating film by the particle dispersion method having many advantages as described above, the conductivity is still lower than that of a sputtering film, etc. There is a problem that it is not yet able to cope with high-definition electrodes, and it is possible to form an ITO powder that can form a coating film that maintains translucency, improves conductivity, and can also be used for the high-definition electrodes. Development is desired.
[0005]
In addition, with respect to the method (A) relating to the conventional method for improving the conductivity from the surface of the particle shape of the powder, although the ITO particles obtained are large and the film resistance is reduced, optical characteristics such as transmittance In particular, there is a problem that a lot of scattered light is generated and the haze of the coating film increases. Regarding the method (B), it is considered that the particles are strip-shaped and good contact can be obtained, but the particles are large, there are the same problems as the method (A), and the conductivity is low. Since the titanium oxide particles are coated with a conductive material, there is a problem that the electrical resistance in the particles is high and sufficient conductivity cannot be obtained in the coating film. In addition, the method (C) is finer than the method (A), and its optical characteristics are slightly improved, but is larger than half the size of the wavelength of visible light (400 to 700 nm). When ITO particles are filled in, scattered light is generated, and there is a problem that sufficient light transmittance of visible light cannot be obtained and haze prevention cannot be achieved. That is, according to the use of acicular ITO particles, although the film resistance is improved, the optical properties related to the scattered light are not sufficient, and there remains a problem that further atomization is required. . Note that the haze is a characteristic relating to the degree of scattering (%) related to the light scattering phenomenon, and the smaller the characteristic of the transparent electrode film, the more preferable the haze depends on the shape and dispersion of the ITO powder particles. It became clear that it was strongly influenced.
[0006]
For this reason, the present inventors made Sn-containing In oxide powder as a conductive material in the coating film by making the ITO powder particle into a needle-like or plate-like shape with a prescribed size and axial ratio. Considering that it is possible to improve conductivity by increasing the contact surface between particles and to suppress scattered light, neutralization treatment of adding an alkali to an acidic aqueous solution containing Sn and In is a process of two or more steps As a result, the present inventors succeeded in producing fine Sn-containing In oxide particles having no agglomeration, and improved the conductivity as compared with the conventional case and suppressed the scattered light to some extent.
However, by making the needle-like ITO powder particles finer in this way, it has been possible to improve the film resistance and maintain a high light transmittance, but in terms of haze suppression and dispersibility compared to granular particles. The pot life is not sufficient, that is, when the coating film is formed by particle aggregation and sedimentation in dispersion stability, particularly storage stability, the light transmittance is not sufficient, and further improvement is desired.
[0007]
In view of such a situation, the present invention has good dispersibility and can be applied to a particle-dispersed slurry, and exhibits excellent optical properties, that is, high translucency and low haze, and high conductivity. The objective is to provide an optimal ITO powder capable of forming a coating film showing a transparent conductive film using the ITO powder.
[0008]
[Means for Solving the Problems]
In order to achieve the above-mentioned object, the present inventors have focused on the shape of fine ITO particles and found out the possibility of achieving high conductivity and high transmittance by combining two or more types of ITO particles. This has led to the present invention.
That is, the present invention firstly includes at least acicular ITO particles and granular ITO particles, and the weight ratio of the acicular ITO particles to the granular ITO particles is 2:98 to 98: 2, and the acicular shape The ITO particles have a major axis length of 0.5 μm or less, a minor axis length of 0.1 μm or less, an axial ratio of 1.5 to 10, and a SnO 2 content of 2 to 20 wt%. The transparent conductive film ITO powder having a SnO 2 content of 2 to 20 wt% and secondly containing at least acicular ITO particles and granular ITO particles, The weight ratio with respect to the granular ITO particles is 20:80 to 80:20, and the acicular ITO particles have a major axis length of 0.5 μm or less, a minor axis length of 0.1 μm or less, and an axial ratio of 1.5 to 10 and SnO 2 content is 2 to 20 wt%, and the granular IT The O particles are made of ITO powder for transparent conductive film having a particle size of 0.05 μm or less and SnO 2 content of 2 to 20 wt%, and thirdly composed of acicular ITO particles and granular ITO particles, The weight ratio between the ITO particles and the granular ITO particles is 2:98 to 98: 2, and the acicular ITO particles have a major axis length of 0.5 μm or less, a minor axis length of 0.1 μm or less, and an axial ratio. 1.5 to 10 and SnO 2 content is 2 to 20 wt%, and the granular ITO particles have a particle size of 0.05 μm or less and SnO 2 content is 2 to 20 wt% for a transparent conductive film Fourth, the ITO powder is composed of acicular ITO particles and granular ITO particles, and the weight ratio of the acicular ITO particles to the granular ITO particles is 20:80 to 80:20, and the acicular ITO The particles have a major axis length of 0.5 μm or less, a minor axis length of 0.1 μm or less, and an axial ratio of .5～10 a and SnO 2 content is 2 to 20 wt%, the particulate ITO particles transparent conductive film for ITO powder and SnO 2 content of the particle diameter is 0.05μm or less is 2 to 20 wt% Fifth, it is made of an ITO powder containing at least acicular ITO particles and granular ITO particles, and the weight ratio of the acicular ITO particles and the granular ITO particles is 2:98 to 98: 2, The acicular ITO particles have a major axis length of 0.5 μm or less, a minor axis length of 0.1 μm or less, an axial ratio of 1.5 to 10, and a SnO 2 content of 2 to 20 wt%. The particle size is 0.05 μm or less, the SnO 2 content is 2 to 20 wt%, the membrane resistance is 10 kΩ / □ or less, the transmittance is 80% or more and the haze value is 2% or less in haze measurement. A transparent conductive film, sixth, at least needle-shaped It consists of ITO powder containing TO particles and granular ITO particles, and the weight ratio of the acicular ITO particles to the granular ITO particles is 20:80 to 80:20, and the acicular ITO particles have a long axis length. 0.5 μm or less, the minor axis length is 0.1 μm or less, the axial ratio is 1.5 to 10 and the SnO 2 content is 2 to 20 wt%. The granular ITO particles have a particle size of 0.05 μm or less and A transparent conductive film having a SnO 2 content of 2 to 20 wt%, a film resistance of 10 kΩ / □ or less, a transmittance of 80% or more and a haze value of 2% or less in haze measurement, Further, it is made of ITO powder composed of acicular ITO particles and granular ITO particles, and the weight ratio of the acicular ITO particles and the granular ITO particles is 2:98 to 98: 2, and the acicular ITO particles are Major axis length is 0.5μm or less, minor axis length is 0.1μm Lower, axial ratio is and SnO 2 content of 2 to 20 wt% 1.5 to 10, wherein the particulate ITO particles is and SnO 2 content of the particle size of 0.05μm or less is 2 to 20 wt%, A transparent conductive film having a film resistance of 10 kΩ / □ or less, a transmittance of 80% or more and a haze value of 2% or less in haze measurement, eighthly, from acicular ITO particles and granular ITO particles The acicular ITO particles and the granular ITO particles have a weight ratio of 20:80 to 80:20, and the acicular ITO particles have a major axis length of 0.5 μm or less and a minor axis length. Is 0.1 μm or less, the axial ratio is 1.5 to 10 and the SnO 2 content is 2 to 20 wt%. The granular ITO particles have a particle size of 0.05 μm or less and the SnO 2 content is 2 to 20 wt%. %, The membrane resistance is 10 kΩ / □ or less, and haze A slurry in which a transparent conductive film having a transmittance of 80% or more and a haze value of 2% or less is mixed, and the needle-like ITO particles and the granular ITO particles are mixed and dispersed in a solvent. Is applied to a transparent plate, and the method for forming a transparent conductive film according to any one of the fifth to eighth aspects is provided.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
The ITO powder for a transparent conductive film in the present invention is basically an ITO powder in which acicular ITO particles and granular ITO particles are mixed, and has good film resistance due to acicular ITO particles and high resistance due to granular ITO particles. Both dispersibility can be achieved. In other words, by improving the dispersibility of fine powder particles due to the presence of granular ITO particles, high optical properties are achieved by suppressing the generation of scattered light while maintaining high film conductivity due to miniaturized acicular ITO particles. That is, haze prevention and high translucency can be obtained. Further, since the dispersibility of the powder particles is improved, the advantages of the coating method are fully utilized. Furthermore, these effects are more certain by using ITO powder having a specific shape and a specific particle size. The needle-like ITO particles in the present invention substantially contain plate-like or flake-like ITO particles, and the granular ITO particles contain substantially spherical ITO particles.
[0010]
The needle-like ITO particles in the mixed ITO powder have a SnO 2 content of 2 to 20 wt%, a long axis length of 0.5 μm or less, preferably 0.2 μm or less, and a short axis length of 0.1 μm or less. Sn-containing In oxide particles having a shape of a plate or a plate, and the ratio of the major axis length / minor axis length is 1.5 to 10.
When the major axis length of the needle-like ITO particles exceeds 0.5 μm, visible light scattering occurs, and optical properties such as translucency and haze deteriorate. In particular, when the major axis length is 0.2 μm or less, the scattering of visible light is further suppressed. On the other hand, if the minor axis length exceeds 0.1 μm, the contact surface between the particles is low and the film conductivity is low, and conversely, if it is 0.05 μm or less, the film conductivity is further improved. Furthermore, when the axial ratio of the major axis length / minor axis length is out of the range of 1.5 to 10, the conductivity, dispersibility, and in-particle crystallinity are deteriorated. The effect of lowering the resistance value cannot be obtained.
[0011]
Production of fine needle-like ITO particles in such fine ITO powder found by the present inventors can be performed, for example, by the following steps.
(1) Preparation of raw material acidic aqueous solution Indium chloride aqueous solution in which In is dissolved in HCl is further dissolved in stannic chloride to prepare an acidic aqueous solution as a starting solution. The In concentration in the liquid is 2 to 50 g / l. Further, Sn content of the final in ITO and 2 to 20 wt% in terms of SnO 2. When it is out of the range of 2 to 20 wt%, the conductivity of the oxide is lowered. The acid to be used is not limited to HCl, and HNO 3 , H 2 SO 4 and the like can also be used. Further, NH 3 , NH 4 OH, NaOH, KOH or the like is used as the alkali in the preliminary neutralization treatment and neutralization treatment.
[0012]
(2) Pre-neutralization and neutralization First, when the temperature of the acidic aqueous solution is 45 ° C. or lower, the alkali is added to pre-neutralize to pH 2-4. Furthermore, in the subsequent neutralization, the temperature is raised in 30 minutes to 2 hours, the temperature of the liquid is raised to 50 ° C. or more, the alkali is added, neutralized to pH 7 to 8 and Sn-containing In as a precursor The hydroxide precipitates and is filtered, washed and dried.
In other words, an acidic aqueous solution containing Sn and In is first formed into fine particle nuclei by pre-neutralization treatment, and then a hydroxide is grown on the outer shell in a higher temperature neutralization process. Alternatively, plate-like hydroxide powder particles can be generated.
[0013]
(3) Firing The obtained Sn-containing In hydroxide is fired, followed by dehydration decomposition and sintering.
The firing atmosphere is an inert gas atmosphere such as nitrogen containing water vapor, and preferably contains a reducing gas such as NH 3 . The firing temperature is 300 to 1000 ° C. By firing in the above temperature and atmosphere, the desired fine acicular or plate-like ITO powder can be obtained while maintaining the shape anisotropy of the hydroxide powder particles.
[0014]
The production of the granular ITO particles used in the finely mixed ITO powder of the present invention belongs to the prior art, and can be performed, for example, as follows.
An acidic aqueous solution obtained by adding stannic chloride to an aqueous hydrochloric acid solution containing In and an alkaline aqueous solution such as NH 4 OH are prepared, and the aqueous alkaline solution is neutralized by adding the alkaline aqueous solution to a pH of about 7 to 8. Is filtered, dehydrated and dried to obtain Sn-containing In hydroxide. By firing this hydroxide in a nitrogen gas atmosphere containing water vapor and NH 3 at a temperature of about 600 to 700 ° C., a granular or spherical shape having a major axis length / minor axis length ratio of about 1 to 2 is obtained. ITO particles can be obtained.
[0015]
The obtained powder of acicular ITO particles and the powder of granular ITO particles are mixed in an arbitrary ratio. That is, it is possible to form a paint slurry by uniformly dispersing and mixing both ITO powders in a solvent. By applying the obtained slurry to a transparent plate such as glass and volatilizing the solvent to fix the film, a transparent conductive coating film having high dispersibility, low haze, high translucency, and low resistance is obtained. Obtainable.
As for mixing with the solvent, the powder of the acicular ITO particles and the powder of the granular ITO particles can be charged and mixed in the solvent at an arbitrary ratio, and the acicular ITO particles can be dispersed in advance. The powder and the powder of the granular ITO particles can be dry-mixed at an arbitrary ratio, and then charged and dispersed in a solvent. Furthermore, a powder in which the needle-like ITO particles and the granular ITO particles are mixed can be manufactured and charged and dispersed in a solvent.
In order to produce a powder in which acicular ITO particles and granular ITO particles are mixed, acicular Sn-containing In hydroxide slurry and granular Sn-containing In hydroxide slurry are mixed, filtered, dehydrated, dried and fired. Can be manufactured. Moreover, after mixing needle-like Sn containing In hydroxide particle | grains and granular Sn containing In hydroxide particle | grains beforehand and making it a slurry, it can filter, spin-dry | dehydrate, dry and bake and can also manufacture.
A conventional method can be used as a method for coating, and an organic solvent such as alcohol, ketone, or ether is added as a solvent, a surfactant or a coupling agent is added as a dispersant, and a dispersing device such as a bead mill is used. To disperse. Alternatively, an organic or inorganic binder that serves as a binder may be added, or a film may be formed on the coating film and fixed after the film is formed with the ITO paint.
[0016]
The mixing ratio of the acicular ITO particles and the granular ITO particles for effectively achieving both the membrane resistance value and the haze prevention is effective in a wide range of 2:98 to 98: 2 by weight ratio, preferably 5 : 95-50: 50, more preferably 5: 95-30: 70.
As described above, the long axis length of the acicular ITO particles is preferably 0.5 μm or less, the short axis length is 0.1 μm or less, the axial ratio is 1.5 to 10, and the SnO 2 content is preferably 2 to 20 wt%. . The granular ITO particles preferably have a particle size of 0.05 μm or less and a SnO 2 content of 2 to 20 wt%.
By using such a transparent conductive film, it is possible to obtain excellent optical characteristics such that the film resistance is 10 kΩ / □ or less, the transmittance is 80% or more, and the haze value is 2% or less in haze measurement.
Note that the effect of the powder mixing method can be obtained by either a dry method or a wet method. Dry mixing with powder has the advantage that productivity can be improved by a single dispersion operation, but it is selected in consideration of facilities and difficulty of operation.
[0017]
【Example】
EXAMPLES The present invention will be further described below with reference to examples and comparative examples, but the technical scope of the present invention is not limited to these examples.
[0018]
[Example 1]
200 g of HCl solution containing 18 wt% of In was adjusted to 2.9 L with pure water, and 5.4 g of stannic chloride was further added to prepare an acidic aqueous solution as a starting solution. Further, 150 g of 25% aqueous ammonia was diluted with 1350 g of pure water to prepare an alkaline solution. Next, a part of the alkaline solution was added to an acidic aqueous solution having a liquid temperature of 20 ° C. for 17 minutes to pre-neutralize the solution to pH 3. Furthermore, the liquid temperature of the preliminary neutralization liquid was raised to 90 ° C., and the remaining alkaline solution was added over 60 minutes. The final pH was 7.5. This was filtered, dehydrated and dried to obtain a precipitate of Sn-containing In hydroxide consisting of needle-like powder particles.
Next, this Sn-containing In hydroxide was put in a tube furnace and baked at 600 ° C. for 2 hours in an atmosphere of nitrogen gas containing 1.5 vol% steam and 0.05 vol% NH 3 gas. The Sn-containing In oxide particles thus obtained, that is, the ITO powder particles having a Sn content of 5 wt%, have an average major axis length of 0.069 μm, an average minor axis length of 0.029 μm, and an average axis ratio of 2.38. It was acicular powder particles having a BET specific surface area of 30.4 m 2 / g and a crystallite diameter Dx of 20.6 nm.
[0019]
Next, granular ITO powder was produced.
An acidic aqueous solution and an alkaline solution were prepared in the same manner as in the case of the needle-shaped particles. The total amount of the alkaline solution was added to the acidic aqueous solution having a liquid temperature of 35 ° C. over 60 minutes, so that the final pH was 7.5. The neutralized solution was filtered, and the filtrate was dehydrated and dried to obtain granular Sn-containing In hydroxide. The obtained Sn-containing In hydroxide powder particles were aggregates having a major axis length of 0.039 μm and a minor axis length of 0.032 μm.
Next, this Sn-containing In hydroxide was put in a tube furnace and baked at 645 ° C. for 2 hours in an atmosphere of nitrogen gas containing 1.5 vol% steam and 0.05 vol% NH 3 . The obtained Sn-containing In oxide powder particles, that is, the ITO powder particles having a Sn content of 5 wt% were in a granular shape. The powder particles had a BET specific surface area of 28 m 2 / g and a crystallite diameter Dx of 260 nm.
[0020]
Both ITO powders obtained as described above were mixed with a mixer at a ratio of 1 g of acicular powder and 4 g of granular powder.
5 g of the mixed powder, 20 g of the mixed solvent (ethanol: propanol = 7: 3) and 0.25 g of an anionic surfactant as a dispersing agent are put in a planetary ball mill (Pitch type P-5 made by Fritche, container capacity 80 ml, PSZ 0.3 mm ball). And rotated for 30 minutes at 300 rpm.
Colloidal silica and ethanol are added to this dispersion to prepare a slurry in which the mixed ITO powder content is 2 wt%, the silica content is 2 wt%, and the balance is ethanol and propanol. The film was dried at 30 ° C. for 30 minutes to obtain a transparent conductive coating film having a thickness of 0.3 μm.
The film resistance of the obtained coating film was measured and found to be 5.3 kΩ / □. Further, when the transmittance and haze were measured according to the method of JIS K7136 using a turbidimeter NDH2000 manufactured by Nippon Denshoku Industries Co., Ltd. as a haze meter, the transmittance was 90% and the haze value was 1%, which was good. It was a transparent conductive film.
[0021]
[Example 2]
A mixed ITO powder having a mixing ratio of 50:50 was obtained by mixing 2.5 g of the acicular ITO powder obtained in Example 1 and 2.5 g of the granular ITO powder with a mixer, and subsequently the same treatment as in Example 1. A slurry was prepared by spin coating on a glass plate and dried to obtain a transparent conductive coating film.
The film resistance of the obtained coating film was 5.2 kΩ / □, the transmittance was 90%, and the haze value was 1.5%.
[0022]
Example 3
A transparent conductive coating film was obtained by the same treatment as in Example 1 except that the acicular ITO powder obtained in Example 1 and the granular ITO powder were mixed at a ratio of 4 g and 1 g.
The film resistance of the obtained coating film was 5.1 kΩ / □, the transmittance was 90%, and the haze value was 2%.
[0023]
[Example 4]
The same procedure as in Example 1 was performed except that the alkali pre-neutralization time in Example 1 was changed from 17 minutes to 13 minutes. The obtained Sn-containing In oxide needle-like particles, that is, ITO powder particles having a Sn content of 5 wt%, have an average major axis length of 0.309 μm, an average minor axis length of 0.071 μm, and an average axis ratio of 4.37. The BET specific surface area was 20.7 m 2 / g and the crystallite diameter Dx was 16.7 nm. Subsequently, a transparent conductive coating film was obtained by the same treatment as in Example 1. The film resistance of the obtained coating film was 5.1 kΩ / □, the transmittance was 90%, and the haze value was 1.1%.
[0024]
[Comparative Example 1]
Using only the granular ITO powder obtained in Example 1, a transparent conductive coating film was obtained by the same treatment as in Example 1.
The film resistance of the obtained coating film was as high as 20 kΩ / □, the transmittance was 90%, and the haze value was 1%.
[0025]
[Comparative Example 2]
Using only the acicular ITO powder obtained in Example 1, a transparent conductive coating film was obtained by the same treatment as in Example 1.
The film resistance of the obtained coating film was 5 kΩ / □, the transmittance was 90%, and the haze value was as high as 5%.
[0026]
The coating films of Examples 1 and Comparative Example 2 are summarized in Table 1.
As is clear from this result, when the mixing ratio of the acicular powder is 0 (in the case of only the granular powder), the dispersibility of the powder is good and the transmittance is high and the haze is suppressed. The membrane resistance is in an abnormally high state. As the mixing ratio of the acicular powder increases, the dispersibility is suppressed and the haze value tends to increase slightly, but the film resistance decreases. When the mixing ratio of the acicular powder is 100% (when the granular powder is 0), the film resistance is further reduced, but the haze is abnormally high. In addition, the dispersibility of the powder is good when the mixing ratio of the acicular powder and the granular powder is at least in the range of 20:80 to 80:20, and both the resistance of the coating film and the haze can be achieved.
[0027]
[Table 1]
【Effect of the invention】
According to the present invention, an ITO powder comprising acicular ITO particles and granular ITO particles, preferably a fine needle-like or plate-like shape having a major axis length and a minor axis length of a predetermined value or less and an axial ratio of a predetermined range. A conductive coating film formed by a slurry of ITO powder in which a granular or spherical ITO powder having a particle size equal to or smaller than a predetermined value is mixed at a predetermined ratio has a good dispersibility of conductive material powder particles. The contact surface between body particles increases, conductivity improves, and the dispersibility of powder particles improves, so scattered light is suppressed, haze is low, translucency is high, and cathode ray tube is enlarged. In addition, there is a remarkable effect that it can be applied by a coating method for high-definition electrodes of display devices, and cost reduction can be realized.
Claims (9)
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| JP2001299862A JP5070554B2 (en) | 2001-09-28 | 2001-09-28 | ITO powder, transparent conductive film and method for forming the same |
| US10/108,618 US6908574B2 (en) | 2001-08-13 | 2002-03-28 | Tin-containing indium oxides, a process for producing them, a coating solution using them and electrically conductive coatings formed of them |
| TW091106612A TWI311983B (en) | 2001-08-13 | 2002-04-02 | Tin-containing indium oxides, a process for producing them, a coating solution using them and electrically conductive coatings formed of them |
| KR1020020031689A KR100670621B1 (en) | 2001-08-13 | 2002-06-05 | Tin-containing indium oxides, a process for producing them, a coating solution using them and electrically conductive coatings formed of them |
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| JP5153541B2 (en) * | 2008-09-24 | 2013-02-27 | Ｄｏｗａエレクトロニクス株式会社 | Method for producing Sn-containing In oxide and method for producing conductive paint |
| JP5486752B2 (en) * | 2009-09-18 | 2014-05-07 | 三菱マテリアル株式会社 | Heat ray shielding composition containing rod-shaped indium tin oxide powder and method for producing the same |
| JP5486751B2 (en) * | 2009-09-18 | 2014-05-07 | 三菱マテリアル株式会社 | Rod-shaped indium tin oxide powder and method for producing the same |
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| JP3251066B2 (en) * | 1992-08-31 | 2002-01-28 | 富士チタン工業株式会社 | Method for producing acicular conductive fine powder |
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