JP4521644B2 - Method for forming photocatalytic film - Google Patents
Method for forming photocatalytic film Download PDFInfo
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- JP4521644B2 JP4521644B2 JP10491499A JP10491499A JP4521644B2 JP 4521644 B2 JP4521644 B2 JP 4521644B2 JP 10491499 A JP10491499 A JP 10491499A JP 10491499 A JP10491499 A JP 10491499A JP 4521644 B2 JP4521644 B2 JP 4521644B2
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- film
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- photocatalyst
- photocatalytic
- forming
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Images
Description
【0001】
【発明の属する技術分野】
本発明は、高活性で強い膜強度の光触媒膜を低温で形成するための方法に関する。
【0002】
【従来の技術】
光触媒にそのバンドギャップ以上のエネルギーを持つ波長の光を照射すると、光励起により伝導帯に電子を、価電子帯に正孔を生じる。この光励起により生じた電子の持つ強い還元力や正孔の持つ強い酸化力は、有機物の分解・浄化、水の分解、窒素酸化物の除去などへの利用が検討されており、抗菌、浄化の分野では一部で実用化が進められている。
【0003】
光触媒は強い分解活性が得られる触媒として、防汚、抗菌、脱臭、NOx等の有害ガスの浄化へと応用検討されてきた。また、光触媒の超親水性効果を利用し、雨滴による洗浄を応用する検討がなされてきた。既に、空気清浄機のフィルタ、道路照明や蛍光灯の防汚、鏡やレンズの防曇や撥水、自動車塗装面の防汚、建材やタイルの防汚にと実用化が大いに図られている。
【0004】
光触媒として、例えば高活性で化学的な安定性に優れた酸化チタンは、微粒子または膜状に形成される。微粒子光触媒は、一般的には接着剤を介して基板上に接着することにより膜状とされる。接着性能を有するバインダーとしては、シリカ系の材料を用いたりフッ素樹脂の材料を用いる。バインダーで光触媒粒子を固定する方法では、バインダー中に光触媒が埋もれて触媒活性が損なわれるのを防ぐため、多孔質な材料を使用する必要がある。さらに、高活性な膜を得るためには、バインダーをできるだけ多孔質にする必要があり、密着性や膜強度が損なわれるという問題があった。
【0005】
一方、バインダーによる光触媒固定方法でも、光触媒活性を犠牲にすることによって密着性の強い膜を作ることができる。比較的弱い光触媒活性でも超親水性が得られるため、雨滴による大きな洗浄効果で防汚することができる。これは、自動車の防汚に実用化されている。しかし、雨滴による洗浄効果を期待できない室内においては、光触媒活性が弱いため防汚効果がほとんど得られないという問題があり、実用的でない。このように、バインダーで光触媒を固定する方法は、原理的に膜強度と活性の両立が困難で、大きな改善が見込めない。
【0006】
そこで、バインダーを使用せずに光触媒材料を直接膜状に形成する一般的な方法として、ゾルゲル法を利用して酸化チタン膜を形成する方法があり、チタンアルコキシドやチタンキレート等の原料液を基板に塗布、乾燥後、500℃以上の高温で焼成を行うことにより光触媒膜を成膜して、光触媒膜を形成する。
【0007】
ゾルゲル法で光触媒膜を直接形成する方法は、バインダーを使用する必要がないため、バインダー中に光触媒が埋もれるといった問題がなく、膜強度が強く高活性な膜を得ることができる。しかも、透明な膜を得ることができるため、下地の色を変えることにより必要に応じて種々の色彩にすることができ、インテリアを重視した用途へも使用できる。
【0008】
【発明が解決しようとする課題】
しかし、ゾルゲル法によって活性のある光触媒膜を得るためには、結晶化する温度まで加熱する必要があり、500℃以上の高温焼成が必要となっている。このため、耐熱性の優れた基板上にのみ形成可能な技術であり、応用できる分野が極めて限られているという問題がある。
【0009】
すなわち、従来のゾルゲル法による光触媒膜の形成方法では、高活性であると同時に密着性、透明性の優れた膜を低温で形成するのが困難であり、プラスチック上に強固に密着するとともに透明性に優れた高活性な光触媒膜を形成することができない。そのため、光触媒の優れた機能を発揮させることができる分野が限られてしまう。
【0010】
本発明は、上記に鑑み、高活性で強い膜強度の光触媒膜を耐熱性の低いプラスチック上に設けることができるように、低温で光触媒膜を形成することを目的とする。
【0011】
【課題を解決するための手段】
本発明による課題解決手段では、耐熱性の低い基板に強固に高活性な光触媒膜を形成するために、一般的な薄膜の形成方法である蒸着法またはスパッタ法を採用するとともに、基板を加熱することなく、しかも基板の温度上昇を抑制しながら成膜できるように、光触媒となる金属原料または金属酸化物原料が置かれた空間内に存在する電子、イオン、活性粒子のエネルギーを利用することにより低温で光触媒膜を形成するものである。活性粒子とは、例えば分子や原子のイオンや電子が存在する空間であるプラズマ中におけるラジカル(遊離原子)、励起された原子や分子であり、化学的に極めて活性な粒子である。そして、これらを利用するためには、低エネルギー励起線の形で基板に照射すればよい。
【0012】
すなわち、蒸着法またはスパッタ法によって金属原料または金属酸化物原料を分子レベルあるいは原子レベルまで一旦分解し、基板上に成膜を行って光触媒膜を形成するが、成膜時に励起線を照射することによって原料分子あるいは原料原子が高エネルギー状態になるため、形成される光触媒膜の結晶化を低温で促進することができ、光触媒膜の結晶性がよくなって高活性化を達成できる。また、励起線を基板に照射することにより、基板の表面が電子やイオンによりきれいになって表面改質され、膜強度が高まる。
【0013】
このように、イオン線、電子線、ラジカル線、プラズマのいずれか1つだけあるいはこれらを複数組み合わせて使用した低エネルギー励起線を耐熱性の低いプラスチック、ゴム、セラミックス等の基板に照射しながら、金属原料または金属酸化物原料を蒸着法またはスパッタ法によって基板に成膜するので、バインダーを用いずに光触媒膜を直接形成でき、バインダー中に光触媒が埋もれるといった問題がなく、高活性な光触媒膜が形成される。また、従来のゾルゲル法では、光触媒膜を結晶化させるために約500℃以上の高温加熱が必要であるが、成膜時に励起線の照射によって原料が高エネルギー状態になるため、基板の加熱が不要となり、低温でも良好に結晶化した膜を形成することができる。また、原料としてチタンあるいは酸化チタンを用いて酸化チタン光触媒膜を形成すると、透明な膜を容易に得ることができる。
【0014】
ここで、励起線における荷電粒子の運動エネルギーを200eV以下にしておくと、発明者らの検討の結果、低温で高活性な光触媒膜を形成できることが明らかになった。運動エネルギーが200eVを超えると、成膜された膜がスパッタされるため、成膜速度が低下して効率的な膜形成ができなくなる。また、高エネルギーの励起線照射になると、基板の表面温度が高くなり、耐熱性の低い基板には適用できないという問題が生じる。
【0015】
基板としてプラスチックを用いる場合、プラスチック製基板の上に光触媒作用を受けない緩衝膜を形成しておくとよい。そして、緩衝膜の上に光触媒膜を形成する。なぜならば光触媒膜は高活性であるので、プラスチックの上に光触媒膜を直接形成すると、光触媒作用によってプラスチックが分解され、変質したり密着性が低下するという問題がある。ところが、プラスチックの上に蒸着法あるいはスパッタ法により一旦緩衝膜を形成しておくと、その上に光触媒膜を形成しても緩衝膜は光触媒によって分解されることはないため、光触媒の活性によってプラスチックが分解されることを防ぐことができる。緩衝膜としては、例えばシリカ、アルミナ、金属等の無機質材料を用いればよく、膜状に形成する。
【0016】
また、無機質材料の代わりに、光触媒作用を受けないフッ素樹脂膜あるいはシリコーン樹脂膜を形成してもよい。フッ素樹脂またはシリコーン樹脂は光触媒によって分解されないので、この緩衝膜上に光触媒膜を形成してもプラスチックはフッ素樹脂あるいはシリコーン樹脂によって保護され、光触媒の活性によってプラスチックが分解されるのを防止することができる。
【0017】
使用するプラスチックとしては、ポリイミド樹脂、ポリエステル樹脂、炭化水素系樹脂、ポリエーテル樹脂、アクリル系樹脂とする。なお、ポリエステル樹脂にはポリカーボネー卜樹脂を含む。炭化水素系樹脂としては、ポリエチレン樹脂、ポリプロピレン樹脂、ポリスチレン樹脂、ABS(アクリロニトリル・ブタジエン・スチレン)樹脂がある。ポリエーテル樹脂としては、ポリアセタール樹脂、ポリフェニレンオキサイド樹脂がある。アクリル系樹脂としてはメチルメタアクリレート樹脂がある。さらに形状としては、板状の成型品あるいはフィルム状とされる。特に、フィルム状であるとフレキシビリティーに優れているので、そのフィルムに光触媒膜を形成した光触媒シートを器具、機器、電化製品、建材等の工業製品の任意の形状をした表面上に合わせて貼り付けることができ、容易に防汚、抗菌、浄化機能を付与することができ、光触媒膜の活用を図れる。
【0018】
ところで、蒸着法やスパッタ法では、膜形成時に基板を薄膜形成装置の真空室内に設置する必要がある。特に、光触媒形成面の表面積が大きい場合、真空室に基板が収容できないことがある。また、真空室に収容できる寸法であっても、真空室に収容できる基板の個数が限られ、生産効率が悪いという問題がある。そこで、フィルム状の基板にすることにより、ロール状に巻くことができるので、巻き付けたフィルムを引き出して、ロールツーロールに巻き取りながら光触媒膜を連続して形成することが可能となる。そのため、生産効率が向上して、生産コストを極めて安くすることができる。しかも、このように作製したフィルムを所定の形状のシートにして工業製品の表面に貼り付けるだけで光触媒膜として使用できるので、光触媒の機能を必要とする工業製品の材質にかかわらず、光触媒膜の形成に適したフィルムを自由に選択することができるという利点がある。
【0019】
また、フッ素樹脂あるいはシリコーン樹脂を基板として用いてもよく、この上に直接光触媒膜を形成することができる。そして、これらの樹脂は比較的柔軟性に優れているので、フィルム状とすることにより、上記の如く生産効率が向上するとともに、基板と光触媒膜との間に緩衝膜を形成する必要がなくなるので、膜形成時間を短縮でき、生産コストを大幅に低減できる。
【0020】
そして、ポリイミド樹脂は、耐熱温度が約300℃と高く、耐熱性が要求される電化製品等の機器の表面に貼り付けるのに適している。また、光触媒膜をフィルム上に形成する際に、ポリイミド樹脂の耐熱温度までフィルムを加熱することができるので、膜強度が高くなり、特に光触媒膜とフィルムとの密着性が優れた信頼性の高い光触媒シートを得ることができる。また、光触媒膜形成時、励起線照射を行うのでフィルムの温度が上昇するが、ポリイミド樹脂は耐熱温度が高いため励起線を充分照射することができ、高活性な光触媒膜が比較的容易に得られる。また、製造時の工程ばらつきによってフィルムの温度が高くなっても、熱によってフィルムが伸びたり劣化するといった問題が発生しにくく、品質のよい光触媒膜が得られる。
【0021】
また、ポリエステル樹脂、ポリカーボネート樹脂、ポリプロピレン樹脂は、安価であると同時に透明性の優れたフィルムを得られる。このため、透明な光触媒シートを形成することができ、インテリア性に配慮した光触媒膜を容易に作製できるという利点がある。また、ポリエステル樹脂、ポリカーボネート樹脂は、安価であるが比較的耐熱性に優れており、製造時の工程ばらつきによってフィルムの温度が上昇してもフィルムが変形しにくく、また比較的高温の使用環境に耐えるという特長があり、高品質な汎用性のある光触媒シートが得られる。ABS樹脂は、安価で家庭用電化製品の外装等に大量に使用されているので、光触媒膜を形成したABS樹脂フィルムは、ABS樹脂を使用した各種機器等に容易に熱圧着をすることができ、同色にすると見栄えがよくなる。
【0022】
そして、本発明の光触媒膜はバインダーを用いていないため透明な膜を形成可能であり、プラスチック上に緩衝膜としてシリカなどの透明な膜を形成することにより、透明な光触媒膜となる。このため、下地の色を変えることにより、必要に応じて種々の色にすることができ、インテリアを重視した用途に使用する場合に最適である。特に、透明な樹脂フィルムを用いることで透明な光触媒シートを容易に作製することができる。家庭用の機器においてはインテリア性が求められるため、必要に応じ種々の色にする必要があるが、透明な光触媒シートを貼り付けると、各種機器等の色を損なうことなくインテリア性に配慮でき、使用範囲が広がる。
【0023】
【発明の実施の形態】
本発明の実施形態に係る光触媒膜の形成に用いる薄膜形成装置を図1に示す。この装置は電子ビーム蒸着装置であり、1は真空室、2は真空排気口、3は電子線4を発生する電子線源、5は蒸着原料、6は励起線源、7は基板ホルダ、8は基板、9は蒸発原料、10はバイアス電源である。
【0024】
そして、板状あるいはフィルム状のプラスチック、ゴム、セラミックス等からなる基板8を基板ホルダ7に固定し、るつぼに無機質材料からなる蒸着原料5を入れ、真空排気して、励起線源6から酸素イオン、酸素ラジカル、酸素プラズマの混合励起線を基板8に照射する。これと同時に蒸着原料5に電子線4を当てて加熱することにより蒸発させ、基板8上に付着させて緩衝膜11を形成する。ここで、無機質材料としては、光触媒作用を受けない材料とされ、具体的にはシリカ、アルミナ、あるいはアルミニウム、銀、銅、亜鉛等の金属である。
【0025】
なお、無機質材料の代わりにフッ素樹脂あるいはシリコーン樹脂を用いると、フッ素樹脂あるいはシリコーン樹脂からなる緩衝膜11が形成される。すなわち、これらの樹脂は光触媒作用を受けず、基板8を光触媒作用から保護する。
【0026】
次に、金属原料または金属酸化物原料からなる蒸着材料5をるつぼに入れ、上記と同様の励起線を基板8に向けて照射しながら、電子線4によって蒸着原料5を蒸発させて分子あるいは原子に分解し、緩衝膜11の上に付着させて金属酸化物からなる光触媒の成膜を行う。これによって、図2に示すような光触媒膜12が形成される。このとき、励起線によって基板8の上に付着した原料が高エネルギー状態になり、基板8を加熱しなくても成膜される光触媒膜12の結晶化が進行する。ここで、金属原料または金属酸化物原料としては、酸化チタン、酸化タングステン、酸化バナジウム、酸化ジルコニウム、またはチタン、タングステン等である。
【0027】
また、基板8として、光触媒によって分解されないフッ素樹脂あるいはシリコーン樹脂を用いる場合には、金属原料または金属酸化物原料からなる蒸着材料5をるつぼに入れ、酸素、イオン、酸素ラジカル、酸素プラズマの混合励起線を基板8に向けて照射しながら、電子線4によって蒸着原料5を蒸発させて分子あるいは原子に分解し、基板8上に直接付着させて金属酸化物からなる光触媒の成膜を行う。これによって、図3に示すような光触媒膜12が形成される。
【0028】
このように、励起線を基板に照射しながら成膜を行うことにより、低温で光触媒膜を形成することができるので、耐熱性の低いプラスチック等の基板にも光触媒膜を形成できる。そして、光触媒膜の結晶化が促進され、単結晶に近くなって、欠陥が少なくなる。したがって、結晶性の高い光触媒膜が得られ、活性が高くなる。また、励起線によって基板の表面あるいは基板上に形成された緩衝膜の表面がきれいにされるとともに凹凸になるので、この表面上に形成される光触媒膜は強固に付着することになり、膜強度が強くなる。なお、蒸着時に導入ガスを必要としないので、形成装置の構造が簡単となり、形成時間も短縮できる。
【0029】
そして、上記のようにプラスチック等の基板上に光触媒膜を形成できるが、実際の使用に際して光触媒作用を発揮させるには、電化製品等の工業製品の表面に形成しなくてはならない。蒸着装置の真空室内に収容できる小型の製品であれば、上記の形成方法によって直接製品の表面に光触媒膜を形成すればよい。製品を真空室内に収容できない場合には、基板をフィルム状として、これに光触媒膜を形成して、製品の形状に応じた光触媒シートにすると、製品の表面に貼り付けることが可能となる。
【0030】
なお、本発明は、上記実施形態に限定されるものではなく、本発明の範囲内で上記実施形態に多くの修正および変更を加え得ることは勿論である。すなわち、蒸着法に代わってスパッタ法を用いても、同様に励起線を照射しながらスパッタリングを行って、光触媒膜を形成することができる。
【0031】
以下、参考例および比較例を示す。
(参考例1)
SiOを蒸着材料として用い、酸素イオン、酸素ラジカル、酸素プラズマの混合励起線を6cm×3cmのポリエステル樹脂の基板に照射しながら、EB(電子ビーム)蒸着法により酸化珪素(シリカ)からなる緩衝膜の成膜を行った。次に、TiOを蒸着材料として用い、酸素イオン、酸素ラジカル、酸素プラズマの混合励起線を基板に照射しながら、EB蒸着法により酸化チタン光触媒の成膜を行った。このとき、基板を保持している基板ホルダにDC電圧を印可し、励起線における荷電粒子の運動エネルギーが80eVになるよう電圧調整を行った。励起線照射は、クライオバック製の励起線源EBS−23を用いた。また、膜厚は3000Åとなるよう成膜時間を調整した。
【0032】
(参考例2)
TiOを蒸着材料として用い、酸素イオン、酸素ラジカル、酸素プラズマの混合励起線を基板に照射しながら、EB蒸着法により酸化チタン光触媒の成膜を行った。なお、基板は6cm×3cmのシリコーン樹脂の基板を用い、励起線照射は、クライオバック製の励起線源EBS−23を用いた。成膜時基板ホルダにDC電圧を印可し、励起線における荷電粒子の運動エネルギーが80eVになるよう調整した。また、膜厚は3000Åとなるよう成膜時間を調整した。
【0033】
(参考例3)
TiOを蒸着材料として用い、酸素イオン、酸素ラジカル、酸素プラズマの混合励起線を基板に照射しながら、EB蒸着法により酸化チタン光触媒の成膜を行った。なお、基板は6cm×3cmのフッ素樹脂の基板を用い、励起線照射は、クライオバック製の励起線源EBS−23を用いた。成膜時基板ホルダにDC電圧を印可し、励起線における荷電粒子の運動エネルギーが80eVになるよう調整した。また、膜厚は3000Åとなるよう成膜時間を調整した。
【0034】
(比較例1)
TiOを蒸着材料として用い、EB蒸着法により酸化チタン光触媒の成膜を行なった。この際、酸素ガス圧が5×10-5Torrになるように酸素ガスを導入した。なお、基板は6cm×3cmのシリコーン樹脂の基板を用いた。また、膜厚は3000Åとなるよう成膜時間を調整した。
【0035】
(比較例2)
TiOを蒸着材料として用い、酸素イオン、酸索ラジカル、酸素プラズマの混合励起線を6cm×3cmのポリエステル樹脂の基板に照射しながら、EB蒸着法により酸化チタン光触媒の成膜を行った。このとき、基板ホルダにDC電圧を印可し、励起線における荷電粒子の運動エネルギーが80eVになるよう電圧調整を行った。励起線照射は、クライオバック製の励起線源EBS−23を用いた。また、膜厚は3000Åとなるよう成膜時間を調整した。
【0036】
(比較例3)
TiOを蒸着材料として用い、酸素イオン、酸素ラジカル、酸索プラズマの混合励起線を基板に照射しながら、EB蒸着法により酸化チタン光触媒の成膜を行つた。なお、基板は6cm×3cmのシリコーン樹脂の基板を用い、励起線照射は、クライオバック製の励起線源EBS−23を用いた。成膜時基板ホルダにDC電圧を印可し、励起線における荷電粒子の運動エネルギーが220eVになるよう調整した。また、膜厚は3000Åとなるよう成膜時間を調整した。
【0037】
5リットルの容器に参考例1〜3および比較例1〜3で得たサンプルを別個に入れ、悪臭物質の1つであるアセトアルデヒドを100ppmの濃度となるよう注入した。次に、6Wのブラックライトを用い、サンプル表面の光触媒膜を紫外線で照射し、アセトアルデヒド濃度が1ppmまで減少する時間を測定した。
【0038】
アセトアルデヒド分解速度測定後、ブラックライトをサンプルに照射して、照射時間の合計が240時間になるまで照射を続けた。その後、サンプルの変色有無および指で擦って光触媒膜の剥離が発生しないかどうかを調べた。その結果を表1に示す。また、各参考例および比較例におけるサンプル作製後の基板変形の有無および成膜速度も表1に示す。
【0039】
【表1】
ポリエステルフィルムにシリカの緩衝膜を形成した後、荷電粒子の運動エネルギーを80eVに設定した励起線を照射しながら、酸化チタン光触媒をEB蒸着で形成した参考例1のサンプルでは、アセトアルデヒドが2.3時間で分解した。基板としてシリコーン樹脂、フッ素樹脂を用いた参考例2および3のサンプルでも、同レベルのアセトアルデヒド分解速度が得られた。一方、酸化チタン成膜時、励起線を照射しなかった比較例1のサンプルでは、アセトアルデヒド分解速度が1/10以下と極めて遅くなっている。また、ポリエステルフィルムの上に緩衝膜を設けず、酸化チタン光触媒膜を直接成膜した比較例2のサンプルでは、アセトアルデヒド分解速度は参考例1〜3のサンプルと同レベルであるが、240時間ブラックライト照射後に、基板の変色が見られた。また、密着強度が低下し、膜の剥離が見られた。シリコーン樹脂やフッ素樹脂およびシリカは、光触媒による分解作用をほとんど受けないが、ポリエステルは光触媒による分解作用を受けるため、基板の変色や密着強度の低下が発生したものと考えられる。
【0040】
酸化チタン光触媒膜形成時の励起線強度を200eV以上に大きくした比較例3のサンプルでは、アセトアルデヒド分解速度は参考例1〜3のサンプルと同レベルとなったが、成膜速度が参考例1〜3のサンプルの半分以下となった。また、成膜後、基板が変形していた。すなわち、励起線強度が強すぎるため、基板上に形成された膜が励起線によってスパッタされ、成膜速度が小さくなっていると考えられる。また、励起線の照射強度が強いため、基板の温度が高くなり、基板の熱変形が生じたと考えられる。
【0041】
(参考例4)
6cm×3cmの白色ABS樹脂の基板表面に、参考例1によって作製した光触媒膜のサンプルをエポキシ樹脂で接着した。
【0042】
(比較例4)
6cm×3cmの白色ABS樹脂の基板を比較例4として使用した。
【0043】
参考例4および比較例4のサンプルを1m3のアクリル製のボックスに入れ、たばこを10本燃焼させた。各サンプルをボックスから取り出した後、サンプルの色を確認した。次に、サンプルから10cmの距離をおいて6W白色蛍光灯を240時間照射した。その後、各サンプルの色を調べた。結果を表2に示す。
【0044】
【表2】
参考例4および比較例4のサンプルはいずれも、蛍光灯照射前はたばこの煙によって汚れて黄色の着色が見られた。しかし、参考例4のサンプルでは、蛍光灯照射後たばこによる黄色の着色が消えて白色になっており、光触媒の作用による浄化作用が見られた。一方、光触媒膜を形成していない比較例4のサンプルでは、蛍光灯照射後もたばこ汚れが残ったままであり、着色が見られた。
【0045】
【発明の効果】
以上の説明から明らかな通り、本発明による光触媒膜形成方法では、励起線を照射をしながら成膜を行うことにより、膜強度の高い高活性な光触媒膜を低温で形成することができる。このため、耐熱温度の低いABS樹脂等のプラスチックにも高活性な光触媒膜を形成することができる。
【0046】
ここで、基板として、フッ素樹脂、シリコーン樹脂によって緩衝膜を形成したフィルム状基板を用いると、膜強度の劣化が起きない高信頼性の光触媒シートが得られる。このような光触媒シートは柔軟性があるので、各種工業製品の表面に応じて容易に貼り付けることができ、防汚や脱臭といった光触媒による機能をあらゆるところで発揮させることができる。
【0047】
また、高活性であると同時に透明性の優れた光触媒膜を得ることができるため、ポリエステル樹脂、ポリカーボネート樹脂、ポリプロピレン樹脂などの透明なフィルム上に光触媒膜を形成すると、透明な光触媒シートを作製することができる。したがって、下地の色調を変えることによって、光触媒シートは必要に応じて各種の色にすることができるので、インテリア性に配慮した工業製品、特に電化製品等の家庭用機器に光触媒の機能を付加する場合に適している。
【図面の簡単な説明】
【図1】本発明の光触媒膜を形成するための成膜装置の概略構成図
【図2】緩衝膜を形成した光触媒シートの断面図
【図3】光触媒シートの断面図
【符号の説明】
1 真空室
2 真空排気口
3 電子線源
4 電子線
5 蒸着原料
6 励起線源
7 基板ホルダ
8 基板
9 蒸発原料
10 バイアス電源
11 緩衝膜
12 光触媒膜[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for forming a photocatalytic film having high activity and strong film strength at a low temperature.
[0002]
[Prior art]
When the photocatalyst is irradiated with light having a wavelength having energy equal to or greater than the band gap, electrons are generated in the conduction band and holes are generated in the valence band by photoexcitation. The strong reducing power of electrons generated by this photoexcitation and the strong oxidizing power of holes have been investigated for use in the decomposition and purification of organic substances, the decomposition of water, the removal of nitrogen oxides, etc. Practical use is being promoted in some areas.
[0003]
Photocatalysts have been studied for application to antifouling, antibacterial, deodorizing, and purification of noxious gases such as NOx as a catalyst that provides a strong decomposition activity. In addition, studies have been made to apply washing with raindrops utilizing the superhydrophilic effect of the photocatalyst. Already, it has been put to practical use for air cleaner filters, road lighting and fluorescent lamp antifouling, antifogging and water repellency of mirrors and lenses, antifouling of painted surfaces of automobiles, and antifouling of building materials and tiles. .
[0004]
As a photocatalyst, for example, titanium oxide having high activity and excellent chemical stability is formed in the form of fine particles or a film. The fine particle photocatalyst is generally formed into a film by adhering onto a substrate via an adhesive. As the binder having adhesive performance, a silica-based material or a fluororesin material is used. In the method of fixing the photocatalyst particles with the binder, it is necessary to use a porous material in order to prevent the photocatalyst from being buried in the binder and impairing the catalytic activity. Furthermore, in order to obtain a highly active film, it is necessary to make the binder as porous as possible, and there is a problem that adhesion and film strength are impaired.
[0005]
On the other hand, even with a photocatalyst fixing method using a binder, a film having strong adhesion can be formed by sacrificing photocatalytic activity. Since superhydrophilicity can be obtained even with relatively weak photocatalytic activity, antifouling can be achieved with a large washing effect by raindrops. This has been put to practical use for antifouling of automobiles. However, in a room where a cleaning effect due to raindrops cannot be expected, there is a problem that the antifouling effect is hardly obtained due to weak photocatalytic activity, which is not practical. Thus, in the method of fixing the photocatalyst with the binder, it is difficult in principle to satisfy both the film strength and the activity, and a great improvement cannot be expected.
[0006]
Therefore, as a general method of directly forming a photocatalytic material into a film without using a binder, there is a method of forming a titanium oxide film using a sol-gel method, and a raw material liquid such as titanium alkoxide or titanium chelate is used as a substrate. After coating and drying, a photocatalyst film is formed by baking at a high temperature of 500 ° C. or higher to form a photocatalyst film.
[0007]
The method of directly forming a photocatalyst film by the sol-gel method does not require the use of a binder, so that there is no problem that the photocatalyst is buried in the binder, and a highly active film having high film strength can be obtained. In addition, since a transparent film can be obtained, various colors can be obtained as required by changing the color of the base, and it can also be used for applications that place importance on the interior.
[0008]
[Problems to be solved by the invention]
However, in order to obtain an active photocatalytic film by the sol-gel method, it is necessary to heat to a crystallization temperature, and high-temperature baking at 500 ° C. or higher is necessary. For this reason, it is a technique that can be formed only on a substrate having excellent heat resistance, and there is a problem that the fields that can be applied are extremely limited.
[0009]
That is, in the conventional photocatalyst film formation method by the sol-gel method, it is difficult to form a film having high activity and at the same time excellent adhesion and transparency at a low temperature. It is impossible to form a highly active photocatalytic film excellent in the above. Therefore, the field | area which can exhibit the outstanding function of a photocatalyst will be restricted.
[0010]
In view of the above, an object of the present invention is to form a photocatalytic film at a low temperature so that a photocatalytic film having high activity and strong film strength can be provided on a plastic having low heat resistance.
[0011]
[Means for Solving the Problems]
In the problem-solving means according to the present invention, a vapor deposition method or a sputtering method, which is a general thin film formation method, is employed and a substrate is heated in order to form a strong and highly active photocatalytic film on a substrate having low heat resistance. By using the energy of electrons, ions, and active particles existing in the space where the metal raw material or metal oxide raw material that becomes the photocatalyst is placed so that the film formation can be performed without suppressing the temperature rise of the substrate. A photocatalytic film is formed at a low temperature. Active particles are, for example, radicals (free atoms) in plasma, which are spaces in which ions and electrons of molecules and atoms exist, and excited atoms and molecules, which are chemically extremely active particles. And in order to utilize these, what is necessary is just to irradiate a board | substrate in the form of a low energy excitation line | wire.
[0012]
That is, the metal raw material or metal oxide raw material is once decomposed to the molecular level or atomic level by vapor deposition or sputtering, and a photocatalytic film is formed on the substrate to form the photocatalytic film. Since the raw material molecules or the raw material atoms are in a high energy state, crystallization of the formed photocatalytic film can be promoted at a low temperature, and the crystallinity of the photocatalytic film is improved and high activation can be achieved. In addition, by irradiating the substrate with excitation rays, the surface of the substrate is cleaned by electrons and ions to be surface modified, and the film strength is increased.
[0013]
In this way, while irradiating a substrate of low heat resistance plastic, rubber, ceramics, etc. with low energy excitation rays using only one of ion beam, electron beam, radical beam, plasma or a combination of these, Since a metal raw material or metal oxide raw material is deposited on a substrate by vapor deposition or sputtering, a photocatalytic film can be directly formed without using a binder, and there is no problem that the photocatalyst is buried in the binder. It is formed. In addition, in the conventional sol-gel method, high temperature heating of about 500 ° C. or more is necessary to crystallize the photocatalyst film. However, since the raw material is brought into a high energy state by irradiation of excitation rays at the time of film formation, A film that is unnecessary and can be crystallized well even at low temperatures can be formed. Further, when a titanium oxide photocatalyst film is formed using titanium or titanium oxide as a raw material, a transparent film can be easily obtained.
[0014]
Here, when the kinetic energy of the charged particles in the excitation line is set to 200 eV or less, as a result of investigations by the inventors, it has become clear that a highly active photocatalytic film can be formed at a low temperature. When the kinetic energy exceeds 200 eV, the deposited film is sputtered, so that the deposition rate is reduced and efficient film formation cannot be performed. In addition, when high-energy excitation beam irradiation is applied, the surface temperature of the substrate becomes high, which causes a problem that it cannot be applied to a substrate having low heat resistance.
[0015]
When plastic is used as the substrate, a buffer film that does not receive photocatalysis is preferably formed on the plastic substrate. Then, a photocatalytic film is formed on the buffer film. This is because the photocatalytic film is highly active, and therefore, if the photocatalytic film is formed directly on the plastic, the plastic is decomposed by the photocatalytic action, and there is a problem that the quality is deteriorated or the adhesion is lowered. However, once the buffer film is formed on the plastic by vapor deposition or sputtering, the buffer film is not decomposed by the photocatalyst even if the photocatalyst film is formed thereon. Can be prevented from being decomposed. As the buffer film, for example, an inorganic material such as silica, alumina, or metal may be used, and the buffer film is formed in a film shape.
[0016]
Further, instead of the inorganic material, a fluororesin film or a silicone resin film that does not receive a photocatalytic action may be formed. Since the fluororesin or silicone resin is not decomposed by the photocatalyst, even if the photocatalytic film is formed on the buffer film, the plastic is protected by the fluororesin or silicone resin, and it is possible to prevent the plastic from being decomposed by the activity of the photocatalyst. it can.
[0017]
The plastic used is a polyimide resin, a polyester resin, a hydrocarbon resin, a polyether resin, or an acrylic resin. The polyester resin includes a polycarbonate resin. Examples of the hydrocarbon resin include polyethylene resin, polypropylene resin, polystyrene resin, and ABS (acrylonitrile / butadiene / styrene) resin. Examples of polyether resins include polyacetal resins and polyphenylene oxide resins. Acrylic resin includes methyl methacrylate resin. Further, the shape is a plate-shaped molded product or a film. In particular, since it is excellent in flexibility when it is in the form of a film, the photocatalyst sheet in which the photocatalyst film is formed on the film is put on the surface of any shape of industrial products such as appliances, equipment, electrical appliances, and building materials. It can be pasted, can easily impart antifouling, antibacterial, and purification functions, and can utilize a photocatalytic film.
[0018]
By the way, in the vapor deposition method or the sputtering method, it is necessary to install the substrate in the vacuum chamber of the thin film forming apparatus during film formation. In particular, when the surface area of the photocatalyst formation surface is large, the substrate may not be accommodated in the vacuum chamber. Further, even if the dimensions can be accommodated in the vacuum chamber, there is a problem that the number of substrates that can be accommodated in the vacuum chamber is limited and the production efficiency is poor. Therefore, since a film-like substrate can be wound into a roll, it is possible to continuously form a photocatalytic film while drawing the wound film and winding it on a roll-to-roll. Therefore, production efficiency can be improved and production cost can be reduced extremely. Moreover, since the film produced in this way can be used as a photocatalyst film simply by sticking it to the surface of an industrial product in a sheet having a predetermined shape, the photocatalyst film can be used regardless of the material of the industrial product that requires the photocatalytic function. There is an advantage that a film suitable for formation can be freely selected.
[0019]
Moreover, you may use a fluororesin or a silicone resin as a board | substrate, and can form a photocatalyst film | membrane directly on this. And since these resins are relatively excellent in flexibility, by making them into a film, production efficiency is improved as described above, and it is not necessary to form a buffer film between the substrate and the photocatalytic film. The film formation time can be shortened and the production cost can be greatly reduced.
[0020]
The polyimide resin has a high heat resistance temperature of about 300 ° C., and is suitable for being attached to the surface of an appliance such as an electric appliance that requires heat resistance. Further, when the photocatalytic film is formed on the film, the film can be heated to the heat resistant temperature of the polyimide resin, so that the film strength is increased, and particularly, the adhesion between the photocatalytic film and the film is excellent and highly reliable. A photocatalytic sheet can be obtained. In addition, the temperature of the film rises due to the irradiation of the excitation line when forming the photocatalyst film, but the polyimide resin can sufficiently irradiate the excitation line because the heat-resistant temperature is high, and a highly active photocatalyst film can be obtained relatively easily. It is done. Moreover, even if the temperature of the film increases due to process variations at the time of manufacture, the problem that the film is stretched or deteriorated by heat hardly occurs, and a high-quality photocatalytic film can be obtained.
[0021]
Polyester resins, polycarbonate resins, and polypropylene resins are inexpensive and at the same time provide a film with excellent transparency. For this reason, there is an advantage that a transparent photocatalyst sheet can be formed and a photocatalyst film in consideration of interior properties can be easily produced. Polyester resins and polycarbonate resins are inexpensive but relatively excellent in heat resistance, and even if the temperature of the film rises due to process variations during manufacturing, the film is not easily deformed, and it can be used in a relatively high temperature environment. A high-quality and versatile photocatalytic sheet can be obtained. Since ABS resin is inexpensive and used in large quantities for exteriors of household appliances, the ABS resin film with a photocatalyst film can be easily thermocompression bonded to various devices using ABS resin. The same color will improve the appearance.
[0022]
Since the photocatalyst film of the present invention does not use a binder, a transparent film can be formed. By forming a transparent film such as silica on the plastic as a buffer film, a transparent photocatalyst film is obtained. For this reason, by changing the color of the base, it is possible to obtain various colors as required, which is optimal when used for applications that place importance on the interior. In particular, a transparent photocatalyst sheet can be easily produced by using a transparent resin film. In home appliances, interior properties are required, so it is necessary to use various colors as necessary, but if you paste a transparent photocatalyst sheet, you can consider interior properties without damaging the color of various devices, etc. Wide range of use.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
A thin film forming apparatus used for forming a photocatalytic film according to an embodiment of the present invention is shown in FIG. This apparatus is an electron beam vapor deposition apparatus, wherein 1 is a vacuum chamber, 2 is a vacuum exhaust port, 3 is an electron beam source that generates an
[0024]
Then, a
[0025]
When a fluororesin or a silicone resin is used instead of the inorganic material, the buffer film 11 made of the fluororesin or the silicone resin is formed. That is, these resins are not subjected to photocatalysis and protect the
[0026]
Next, a
[0027]
When a fluororesin or silicone resin that is not decomposed by a photocatalyst is used as the
[0028]
In this way, by performing film formation while irradiating the substrate with excitation rays, a photocatalytic film can be formed at a low temperature, so that the photocatalytic film can also be formed on a substrate such as plastic having low heat resistance. Then, crystallization of the photocatalyst film is promoted and becomes closer to a single crystal, and defects are reduced. Therefore, a photocatalytic film having high crystallinity is obtained, and the activity becomes high. Moreover, since the surface of the substrate or the surface of the buffer film formed on the substrate is cleaned by the excitation lines and becomes uneven, the photocatalytic film formed on this surface adheres firmly, and the film strength is increased. Become stronger. In addition, since no introduction gas is required at the time of vapor deposition, the structure of the forming apparatus is simplified and the forming time can be shortened.
[0029]
As described above, a photocatalytic film can be formed on a substrate made of plastic or the like, but it must be formed on the surface of an industrial product such as an electric appliance in order to exert a photocatalytic action in actual use. In the case of a small product that can be accommodated in the vacuum chamber of the vapor deposition apparatus, a photocatalytic film may be directly formed on the surface of the product by the above-described forming method. When the product cannot be accommodated in the vacuum chamber, the substrate can be formed into a film, a photocatalytic film is formed on the substrate, and a photocatalytic sheet according to the shape of the product can be attached to the surface of the product.
[0030]
In addition, this invention is not limited to the said embodiment, Of course, many corrections and changes can be added to the said embodiment within the scope of the present invention. That is, even if the sputtering method is used instead of the vapor deposition method, the photocatalytic film can be formed by performing sputtering while irradiating the excitation beam in the same manner.
[0031]
Reference examples and comparative examples are shown below.
(Reference Example 1)
A buffer film made of silicon oxide (silica) by an EB (electron beam) vapor deposition method using SiO as a vapor deposition material and irradiating a 6 cm × 3 cm polyester resin substrate with mixed excitation lines of oxygen ions, oxygen radicals, and oxygen plasma. The film was formed. Next, using TiO as a deposition material, a titanium oxide photocatalyst was formed by EB deposition while irradiating the substrate with mixed excitation lines of oxygen ions, oxygen radicals, and oxygen plasma. At this time, a DC voltage was applied to the substrate holder holding the substrate, and the voltage was adjusted so that the kinetic energy of the charged particles in the excitation line was 80 eV. Excitation line irradiation was performed using an excitation line source EBS-23 manufactured by Cryobach. The film formation time was adjusted so that the film thickness was 3000 mm.
[0032]
(Reference Example 2)
Using TiO as a deposition material, a titanium oxide photocatalyst was formed by EB deposition while irradiating the substrate with mixed excitation lines of oxygen ions, oxygen radicals, and oxygen plasma. In addition, the board | substrate of 6 cm x 3 cm silicone resin was used for the board | substrate, and the excitation ray source EBS-23 made from cryoback was used for excitation ray irradiation. A DC voltage was applied to the substrate holder during film formation, and the kinetic energy of charged particles in the excitation line was adjusted to 80 eV. The film formation time was adjusted so that the film thickness was 3000 mm.
[0033]
(Reference Example 3)
Using TiO as a deposition material, a titanium oxide photocatalyst was formed by EB deposition while irradiating the substrate with mixed excitation lines of oxygen ions, oxygen radicals, and oxygen plasma. The substrate used was a 6 cm × 3 cm fluororesin substrate, and excitation beam irradiation was performed using an excitation beam source EBS-23 manufactured by Cryoback. A DC voltage was applied to the substrate holder during film formation, and the kinetic energy of charged particles in the excitation line was adjusted to 80 eV. The film formation time was adjusted so that the film thickness was 3000 mm.
[0034]
(Comparative Example 1)
Using TiO as a deposition material, a titanium oxide photocatalyst was formed by EB deposition. At this time, oxygen gas was introduced so that the oxygen gas pressure was 5 × 10 −5 Torr. A 6 cm × 3 cm silicone resin substrate was used as the substrate. The film formation time was adjusted so that the film thickness was 3000 mm.
[0035]
(Comparative Example 2)
Using TiO as a deposition material, a titanium oxide photocatalyst was formed by EB deposition while irradiating a 6 cm × 3 cm polyester resin substrate with mixed excitation lines of oxygen ions, acid radicals, and oxygen plasma. At this time, a DC voltage was applied to the substrate holder, and the voltage was adjusted so that the kinetic energy of the charged particles in the excitation line was 80 eV. Excitation line irradiation was performed using an excitation line source EBS-23 manufactured by Cryobach. The film formation time was adjusted so that the film thickness was 3000 mm.
[0036]
(Comparative Example 3)
Using TiO as a deposition material, a titanium oxide photocatalyst was formed by EB deposition while irradiating the substrate with mixed excitation lines of oxygen ions, oxygen radicals, and acid plasma. In addition, the board | substrate of 6 cm x 3 cm silicone resin was used for the board | substrate, and the excitation ray source EBS-23 made from cryoback was used for excitation ray irradiation. A DC voltage was applied to the substrate holder during film formation, and the kinetic energy of charged particles in the excitation line was adjusted to 220 eV. The film formation time was adjusted so that the film thickness was 3000 mm.
[0037]
The samples obtained in Reference Examples 1 to 3 and Comparative Examples 1 to 3 were separately placed in a 5 liter container, and acetaldehyde, which is one of malodorous substances, was injected to a concentration of 100 ppm. Next, using a 6 W black light, the photocatalytic film on the sample surface was irradiated with ultraviolet rays, and the time for the acetaldehyde concentration to decrease to 1 ppm was measured.
[0038]
After measuring the acetaldehyde decomposition rate, the sample was irradiated with black light, and irradiation was continued until the total irradiation time reached 240 hours. Thereafter, it was examined whether the sample was discolored and whether the photocatalyst film was peeled off by rubbing with a finger. The results are shown in Table 1. Table 1 also shows the presence / absence of substrate deformation and the film formation rate after sample preparation in each reference example and comparative example.
[0039]
[Table 1]
In the sample of Reference Example 1 in which a titanium oxide photocatalyst was formed by EB deposition while irradiating an excitation line with a kinetic energy of charged particles set to 80 eV after forming a silica buffer film on a polyester film, acetaldehyde was 2.3. Decomposed in time. Even in the samples of Reference Examples 2 and 3 using a silicone resin and a fluororesin as the substrate, the same level of acetaldehyde decomposition rate was obtained. On the other hand, in the sample of Comparative Example 1 that was not irradiated with the excitation beam during the titanium oxide film formation, the acetaldehyde decomposition rate was extremely slow as 1/10 or less. Further, in the sample of Comparative Example 2 in which the buffer film was not provided on the polyester film and the titanium oxide photocatalyst film was directly formed, the acetaldehyde decomposition rate was the same level as the samples of Reference Examples 1 to 3, but the black for 240 hours After light irradiation, discoloration of the substrate was observed. In addition, the adhesion strength was reduced, and peeling of the film was observed. Silicone resin, fluororesin, and silica are hardly subjected to decomposition by the photocatalyst, but polyester is subjected to decomposition by the photocatalyst, so that it is considered that the substrate is discolored and the adhesion strength is reduced.
[0040]
In the sample of Comparative Example 3 in which the excitation line intensity at the time of forming the titanium oxide photocatalyst film was increased to 200 eV or more, the acetaldehyde decomposition rate was the same level as the samples of Reference Examples 1 to 3, but the film formation rate was Less than half of the three samples. Further, the substrate was deformed after the film formation. That is, since the excitation line intensity is too strong, it is considered that the film formed on the substrate is sputtered by the excitation line and the film formation rate is reduced. Further, since the irradiation intensity of the excitation beam is strong, it is considered that the temperature of the substrate is increased and the substrate is thermally deformed.
[0041]
(Reference Example 4)
The sample of the photocatalyst film produced in Reference Example 1 was adhered to the surface of a 6 cm × 3 cm white ABS resin with an epoxy resin.
[0042]
(Comparative Example 4)
A 6 cm × 3 cm white ABS resin substrate was used as Comparative Example 4.
[0043]
The samples of Reference Example 4 and Comparative Example 4 were placed in a 1 m 3 acrylic box, and 10 cigarettes were burned. After removing each sample from the box, the color of the sample was confirmed. Next, a 6 W white fluorescent lamp was irradiated for 240 hours at a distance of 10 cm from the sample. Thereafter, the color of each sample was examined. The results are shown in Table 2.
[0044]
[Table 2]
The samples of Reference Example 4 and Comparative Example 4 were both stained with cigarette smoke and yellowed before the fluorescent lamp was irradiated. However, in the sample of Reference Example 4, the yellow coloration caused by the cigarette after irradiation with the fluorescent lamp disappeared and turned white, and a purification action due to the action of the photocatalyst was observed. On the other hand, in the sample of Comparative Example 4 in which no photocatalytic film was formed, tobacco stains remained after irradiation with a fluorescent lamp, and coloring was observed.
[0045]
【The invention's effect】
As is clear from the above description, in the photocatalyst film forming method according to the present invention, a highly active photocatalyst film having high film strength can be formed at a low temperature by performing film formation while irradiating excitation rays. For this reason, a highly active photocatalytic film can be formed also on plastics such as ABS resin having a low heat-resistant temperature.
[0046]
Here, as the substrate, off fluororesin, the use of film-like substrate formed with the buffer layer by a silicone resin, the deterioration of the film strength reliability of the photocatalyst sheet does not occur is obtained. Since such a photocatalyst sheet is flexible, it can be easily attached according to the surface of various industrial products, and the functions of the photocatalyst such as antifouling and deodorization can be exhibited everywhere.
[0047]
In addition, since a photocatalytic film having high activity and excellent transparency can be obtained, a transparent photocatalytic sheet is produced when a photocatalytic film is formed on a transparent film such as polyester resin, polycarbonate resin, or polypropylene resin. be able to. Therefore, by changing the color tone of the base, the photocatalyst sheet can be changed to various colors as necessary, so that the photocatalyst function is added to household appliances such as industrial products that are considered to be interior, especially electrical appliances. Suitable for cases.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a film forming apparatus for forming a photocatalytic film of the present invention. FIG. 2 is a cross-sectional view of a photocatalytic sheet on which a buffer film is formed. FIG. 3 is a cross-sectional view of a photocatalytic sheet.
DESCRIPTION OF SYMBOLS 1
Claims (5)
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