JP4323216B2

JP4323216B2 - Photocatalyst-coated metal plate excellent in wear resistance, stain resistance, and coating film adhesion and method for producing the same

Info

Publication number: JP4323216B2
Application number: JP2003134362A
Authority: JP
Inventors: 節子小浦; 淳梶本; 佳子坂本; 克全阿波; 浩茂中村; 智訓牧野
Original assignee: Nippon Steel Nisshin Co Ltd
Current assignee: Nippon Steel Nisshin Co Ltd
Priority date: 2003-05-13
Filing date: 2003-05-13
Publication date: 2009-09-02
Anticipated expiration: 2023-05-13
Also published as: JP2004338114A

Description

【０００１】
【産業上の利用分野】
本発明は、雨水や紫外線照射に曝される屋外環境下においても長期間にわたって清浄表面を維持する塗装金属板及びその製造方法に関する。
【０００２】
【従来の技術】
ＴｉＯ₂を始めとする光触媒は、紫外線照射で活性化し、有機物，ＮＯx，ＳＯx等を分解する作用を呈する。光触媒の光触媒作用を活用し、たとえばアナターゼ型チタニア粉末を配合した塗膜を基材・金属板の表面に設けることにより、セルフクリーニング作用を付与することが検討されている。
この種の塗装金属板でベースとなる塗膜に有機物を使用すると、光触媒反応で生成したＯ₂ ^-，ＯＨラジカル等の活性酸素によって有機塗膜が分解される。有機塗膜の分解は、チョーキング現象となって塗膜剥離に至る。光触媒反応による塗膜の分解は、無機物をベース樹脂に使用することにより解消される（特開平7−113272号公報，特開平8−164334号公報，WO96／29375等参照）。
【０００３】
【発明が解決しようとする課題】
ＴｉＯ₂添加で光触媒活性を付与した無機塗膜は、耐候性に優れているものの、無機塗膜を基材表面に形成する過程でクラックが発生し塗膜剥離に至るケースや、塗装金属板を屋外に設置した後の熱変化に伴う歪みで塗膜剥離が生じるケースが多い。
塗膜剥離の防止対策としては、基材・金属板と無機塗膜の間にエポキシ等の有機プライマ層を介在させる方法，無機塗膜に有機物を配合する方法等が採用されている。しかし、３コート方式は、製造コストを上昇させるばかりでなく、トップ層に含まれている光触媒が有機プライマ層を分解する虞がある。無機塗膜に有機物を配合する方法では、依然としてチョーキング現象が避けられず，塗膜の耐候性が低下しやすい。
【０００４】
【課題を解決するための手段】
本発明は、このような問題を解消すべく案出されたものであり、無機塗膜を形成するシリカ系バインダの分子量，塗膜構造を適正管理することにより、塗膜剥離の原因となる応力を緩和し、基材・金属板に無機塗膜を直接形成する２コート仕様においても塗膜剥離を抑制し、しかも優れた耐摩耗性，光触媒活性が付与された光触媒塗装金属板を提供することを目的とする。
【０００５】
本発明の光触媒塗装金属板は、無機顔料を含むプライマ層，光触媒及び無機顔料を含むトップ層が基材表面に順次形成されており、プライマ層及びトップ層がスチレン換算分子量：３００以上の分子集合体からなるシリカ系バインダを含み、式(１)で算出される吸光度ピークの高さの比率Ａが１.０５〜１.２５の範囲となるようにトップ層の表層部が構造制御されていることを特徴とする。
高さの比率Ａ=(1020ｃｍ^-1ピーク高さ／1090ｃｍ^-1ピーク高さ)……(１)
トップ層表層部は、固体^２９Ｓｉ-ＮＭＲの測定でケミカルシフト−４６ppmが０〜２％以下，−５６ppmが２０〜２５％，−６４ppmが３５〜４５％，−９４ppmが０〜５％，−１０１ppmが５〜１０％，残りが−１１０ppmに構造制御されている。
【０００６】
この光触媒塗装金属板は、スチレン換算分子量：３００以上のシリカ系バインダ及び無機顔料分散トナーを含むプライマ塗料を塗装原板に塗布してプライマ層を形成した後、スチレン換算分子量：３００以上のシリカ系バインダ，シラン処理した光触媒粉末及び無機顔料分散トナーを含むトップ塗料を塗布し、１５０〜４００℃で５〜３０分間焼き付けることにより製造される。
【０００７】
シリカ系バインダとしては、固形分比率４０〜７０質量％のシリカ及び３０〜７０質量％のオルガノヒドロキシシラン及びオルガノヒドロキシシランの部分縮合物を水／イソプロパノール／エチレングリコールモノブチルエーテルの混合溶液に分散・溶解させ、液体²⁹Ｓｉ-NMRの測定でケミカルシフト−４７ppmが３％以下，−５６ppmが１５〜２５％，−６５ppmが１５〜２５％，残りが−１１０ppmとなるように調製されている。
【０００８】
【作用】
チタニア等の光触媒を紫外線照射すると、有機物，ＳＯx，ＮＯx等を分解する反応が生じる。分解反応は，紫外線照射によって光触媒の価電子帯にある電子がエネルギーを吸収して伝導体に励起され、価電子帯に正孔が生じ、正孔の強力な酸化力で有機物，ＮＯx，ＳＯx等が酸化分解するものと考えられている。塗膜剥離を防止するために有機物を導入した無機塗膜であっても、光触媒活性によって塗膜中の有機物が分解されるので、塗膜の耐久性，耐剥離性を両立させることが困難である。
【０００９】
本発明者等は、光触媒活性による有機物分解を避け、チョーキングがなく耐剥離性に優れ、且つ光触媒活性が低下しない塗膜を形成する方法を検討する過程で、スチレン換算分子量：３００以上の分子集合体を含むシリカ系バインダをプライマ層，トップ層に使用すると、塗膜の応力緩和に有効な微細クラックが発生し、厚膜の無機塗膜でも塗膜剥離が生じがたく、優れた光触媒活性を呈することを見出した（特願2002−376640号）。
【００１０】
塗膜剥離の抑制に微細クラックが有効であるものの発生量によっては耐摩耗性に劣る場合があるので、光触媒活性を低下させることなく耐塗膜剥離性，耐摩耗性の両立が必要になる。かかる膜性状を備えた塗膜の開発過程で、塗膜構造をも制御するとき光触媒活性の低下なく耐塗膜剥離性，耐摩耗性の双方が高位に安定することを見出した。耐塗膜剥離性，耐摩耗性に及ぼす塗膜構造の影響は、次のように推察される。
【００１１】
無機塗膜は塗膜自体に伸びがないため、厚膜化した塗膜や屋外での使用中に熱変化した塗膜では大きなクラックが発生し、基材・金属板から剥離しやすい。塗膜形成時の塗膜剥離は、塗料を焼成する際に基材・金属板と塗膜との間で異なる熱膨張係数に起因する熱応力によるものと考えられる。屋外での使用中における塗膜剥離も、同様に熱変化で生じた応力が原因と考えられる。
【００１２】
熱応力が塗膜剥離の原因であるとの前提で、熱応力を局部集中することなく塗膜に均一分散させるとき、応力が基材・金属板／塗膜界面の密着力を下回り、塗膜剥離に至らないと推察される。たとえば、塗膜の応力緩和に有効な微細クラックを塗膜形成時に発生させると、厚膜形成時や屋外での使用中に生じる熱変化に起因する大きなクラックの発生に伴う塗膜剥離を防止できる。しかし、塗膜形成時の微細クラックは塗膜の耐摩耗性にとって好ましくないので、塗膜形成時に発生する微細クラックを極力少なくし、しかも屋外使用中での硬化反応の更なる進行を抑えることにより応力の増加を防止することが望まれる。
【００１３】
そこで、本発明者等は、微細クラックの抑制，使用時の硬化反応の抑制に有効な塗膜構造について検討を加えた結果、塗膜を赤外吸収スペクトル回折して得られる式(１)で表される吸光度ピークの高さの比率Ａを１.０５〜１.２５の範囲に制御した塗膜構造が有効であることを解明した。
高さの比率Ａ=(1020ｃｍ^-1ピーク高さ／1090ｃｍ^-1ピーク高さ)……(１)
また、固体^２９Ｓｉ-ＮＭＲの測定でケミカルシフト−４６ppmが０〜２％，−５６ppmが２０〜２５％，−６４ppmが３５〜４５％，−９４ppmが０〜５％，−１０１ppmが５〜１０％，残りが−１１０ppmにトップ層表層部を調質するとき、耐塗膜剥離性，耐摩耗性の双方が更に改善されることが判った。
【００１４】
赤外吸収スペクトルの1020ｃｍ^-1に現れるピークはＳｉ−Ｏ−Ｓｉ，Ｓｉ−ＯＨに相当し、1090ｃｍ^-1に現れるピークはＳｉ−Ｏ−Ｓｉに相当すると考えられる。塗膜形成時の硬化反応がＳｉ−ＯＨの脱水縮合反応であることを考慮すると、Ｓｉ−ＯＨが少ないことは反応点が少なく結合力が弱いことを意味し、Ｓｉ−ＯＨが多いことは反応点が多く結合力は強いものの経時的な反応が更に進行することを意味する。
【００１５】
式(１)で表される高さの比率Ａが１.０５未満の場合、Ｓｉ−ＯＨが少なく微細クラックが形成される結果、塗膜の応力は小さくなるものの耐摩耗性が低下する。逆に、高さの比率Ａが１.２５を超える場合、Ｓｉ−ＯＨが多く、塗膜形成時にクラックが発生しないが、屋外使用中に硬化反応が進行して塗膜剥離に至る大きなクラックが発生しやすい。
【００１６】
高さの比率Ａとクラック発生，耐塗膜剥離性，耐摩耗性との関係は、固体²⁹Ｓｉ-NMRの測定結果からも支持される。ケミカルシフト−４６ppmのピークはオルガノアルコキシシラン由来のＳｉに二つのアルコキシ基又はＯＨ基が結合した構造に相当し、−５６ppmのピークはオルガノアルコキシシラン由来のＳｉに一つのアルコキシ基又はＯＨ基が結合した構造に相当する。そこで、−４６ppm及び−５６ppmのピークを量規制することにより、耐塗膜剥離性，耐摩耗性の両立が可能になる。具体的には、−５６ppmのピークの量が少なすぎると耐摩耗性に劣り、−４６ppm及び−５６ppmのピークの量が多すぎると耐塗膜剥離性に劣るので、−４６ppm，−５６ppmそれぞれのピークの量を０〜２％，２０〜２５％の範囲に調整する。
【００１７】
【実施の形態】
本発明の光触媒塗装金属板は、基材・金属板の上にプライマ層，トップ層を順次積層している。
〔基材・金属板〕
基材・金属板に使用される塗装原板には、普通鋼板，めっき鋼板，ステンレス鋼板，アルミニウム板，アルミニウム合金板，銅板，銅合金板等がある。塗装原板には、必要に応じてアルカリ脱脂，クロメート処理，リン酸塩処理等の塗装前処理が施される。
【００１８】
〔プライマ層〕
液体²⁹Ｓｉ-NMRの測定でケミカルシフト−４７ppmが３％以下，−５６ppmが１５〜２５％，−６５ppmが１５〜２５％，残りが−１１０ppmとなるように調製されたスチレン換算分子量：３００以上のシリカ系バインダを無機顔料分散トナーと配合したプライマ塗料を基材・金属板に塗布し焼き付けると、応力緩和され耐摩耗性に優れたプライマ層が形成される。
【００１９】
シリカ系バインダは、シリカとオルガノヒドロキシシラン及びオルガノヒドロキシシランの部分縮合物からなる固形分を水／イソプロパノール／エチレングリコールモノブチルエーテルの混合溶媒に分散させることにより、液体²⁹Ｓｉ-NMRの測定でケミカルシフト−４７ppmが３％以下，−５６ppmが１５〜２５％，−６５ppmが１５〜２５％，残りが−１１０ppmとなるように調製される。具体的には、シリカ：４０〜７０質量％、オルガノヒドロキシシラン及びオルガノヒドロキシシランの部分縮合物：３０〜６０質量％からなる固形分を水／イソプロパノール／エチレングリコールモノブチルエーテルの混合溶媒に分散させる。必要に応じ、アンモニア水，トリエタノールアミン，ジメチルアミノエーテル等の有機アミン類等によってシリカ系バインダのｐＨ値を３〜６.５（好ましくは、４〜５）に調製するとき、シリカ系バインダの保存安定性が向上する。
【００２０】
オルガノヒドロキシシランは、たとえば一般式ＲＳｉ(ＯＨ)₃〔Ｒは炭素数１〜３のアルキル基，ビニル基，3,4-エポキシシクロヘキシル基，γ-グリシドキシプロピル基，γ-メルカプトプロピル基又はクロロプロピル基〕で表される化合物である。オルガノヒドロキシシランの部分縮合物としては、一般式ＲＳｉ(ＯＨ)₃のオルガノヒドロキシシランを部分縮合することによって得られるオリゴマー等がある。
【００２１】
シリカ系バインダ中の固形分は、コロイダルシリカを核としてオルガノヒドロキシシラン及びオルガノヒドロキシシランの部分縮合物が脱水縮合で結合した分子集合体になっている。分子集合体の分子量や構造は、脱水縮合時のｐＨ値，反応時間，反応温度等で制御できる。分子集合体を、スチレン換算分子量：３００以上，液体²⁹Ｓｉ-NMRの測定でケミカルシフト−４７ppmが３％以下，−５６ppmが１５〜２５％，−６５ppmが１５〜２５％，残りが−１１０ppmとなるように調整するとき、応力が緩和され耐摩耗性にも優れた塗膜が形成される。反応可能なＯＨ基が少なすぎると、多数の微細クラックが形成され塗膜の応力は小さくなるものの耐摩耗性が低下する。逆に、多すぎるＯＨ基では、塗膜形成時にクラックが発生せず、屋外使用中に硬化反応が進行して塗膜剥離に至る大きなクラックが発生する。そこで、ＯＨ基をもつ構造を適正に量規制することにより、耐塗膜剥離性，耐摩耗性の両立が可能になる。
【００２２】
プライマ塗料には、固形分として１０〜８０質量％（好ましくは、２０〜７５質量％）の無機顔料が配合される。無機顔料には、ＳｉＯ₂，Ａｌ₂Ｏ₃又はＺｒＯ₂処理したルチル型チタニア，(Ｃｏ_1/2,Ｎｉ,Ｚｎ_1/2)ＴｉＯ₄，ＣｏＡｌ₂Ｏ₄，Ｃｕ(Ｃｒ,Ｍｎ)₃Ｏ₄，ＴｉＯ₂-ＮｉＯ-Ｓｂ₂Ｏ₅等がある。十分な隠蔽性を得る上では１０質量％以上の無機顔料が必要であるが、８０質量％を超える過剰量の無機顔料を配合すると基材・金属板に対するプライマ層の密着性が低下する。
【００２３】
プライマ塗料は、塗装前処理した基材・金属板に塗布した後、６０〜３５０℃の温度範囲で乾燥・焼き付けられる。６０℃未満の乾燥温度では、プライマ層の乾燥が不十分となり、プライマ層の上に形成されるトップ層にムラが発生しやすくなる。逆に３５０℃を超える加熱温度では、プライマ層に大きなクラックが発生し、基材・金属板からプライマ層が剥離しやすくなる。
【００２４】
〔トップ層〕
プライマ層に塗布したトップ塗料を焼成することにより、耐汚染性，塗膜密着性に優れたトップ層が形成される。トップ塗料は、プライマ塗料と同様なシリカ系バインダにシラン処理した光触媒粉末，無機顔料分散トナーを配合することにより調製される。シリカ系バインダには、固形分として単独配合量で５質量％以上，無機顔料との合計配合量で１０〜８０質量％（好ましくは，２０〜５０質量％）の光触媒粉末が配合される。十分な光触媒活性を得る上で５質量％以上の光触媒粉末を必要とするが、合計配合量が８０質量％を超える過剰量の光触媒粉末を配合するとトップ層の密着性が低下する。
【００２５】
光触媒粉末には、ＴｉＯ₂，ＺｎＯ，ＷＯ₃，ＦｅＴｉＯ₃，ＳｒＴｉＯ₃から選ばれた１種又は２種以上が使用される。なかでも、化学的に安定で活性度が高く安価な微粒子が得られることからアナターゼ型チタニア粉末が好ましい。
塗布されたトップ塗料は、プライマ層形成時の加熱温度より高い１５０〜４００℃の温度範囲で焼成される。塗膜の十分な縮重合に１５０℃以上の加熱温度が必要であるが、４００℃を超える高温に加熱すると塗膜剥離に至るクラックが入りやすい。好適には、塗膜の乾燥を促進させるためプライマ層形成時の加熱温度を８０〜２５０℃に、トップ層形成時の加熱温度を１５０〜４００℃に設定する。
【００２６】
トップ層形成時の温度設定により、プライマ層とトップ層との間に強固な結合が得られ、トップ層形成時の熱処理でプライマ層に対するトップ層の密着性が向上する。その結果、基材・金属板に対する密着性が良好で、塗膜剥離に至ることなく応力緩和された塗膜が形成される。１５０℃未満の焼成温度では焼成不足となり、耐摩耗性が極端に低下する。焼成温度が４００℃を超えると、冷却過程で基材と塗膜の収縮率が極端に変わるため塗膜剥離が発生しやすくなる。
塗膜構造の制御は、トップ層に適度の微細クラックを発生させて光触媒活性を増大させる効果，多数の微細クラック発生による耐摩耗性の低下を防止する効果の両立を可能にする。このようにして得られた光触媒塗装金属板は、優れた耐汚染性及び大気浄化能を活用し、長期間にわたって紫外線照射や雨水に曝される外装建材，外置き式家電機器筐体等に使用される。
【００２７】
【実施例】
〔塗装金属板の製造例１：本発明例〕
板厚１.０ｍｍのSUS304ステンレス鋼板を塗装原板に使用し、アルカリ脱脂，酸洗，水洗，乾燥した。
プライマ塗料は、ジルコニアで表面処理されたルチル型酸化チタン（白色顔料）を水／イソプロパノール／エチレングリコールモノブチルエーテルの混合溶媒に分散させた無機顔料分散トナーとシリカ系バインダとを配合することにより調製した。プライマ塗料を塗装原板に塗布し、１４０℃で２０分焼成することにより乾燥膜厚２５μｍのプライマ層を形成した。
【００２８】
トップ塗料は、プライマ塗料と同じシリカ系バインダ，無機顔料分散トナーに粒径２０ｎｍのアナターゼ型チタニア粉末を水／イソプロパノール／エチレングリコールモノブチルエーテルの混合溶媒に分散させることにより用意した。トップ塗料をプライマ層上に塗布し、２００℃で２０分焼成することにより、乾燥膜厚１０μｍのトップ層を形成した。シリカ系バインダは、液体²⁹Ｓｉ-NMRの測定によるとき、各構造の含有率は、ケミカルシフト−４７ppmが２.０％，−５６ppmが１７.７％，−６５ppmが１７.３％，−１１０ppmが６３.１％であった。
【００２９】
〔塗装金属板の製造例２：本発明例〕
板厚２.５ｍｍのアルミニウム板を塗装原板とし、粒径７ｎｍのアナターゼ型チタニア粉末を使用する以外は製造例１と同じ条件下でプライマ層，トップ層を形成した。
【００３０】
〔塗装金属板の製造例３：比較例〕
反応温度８０℃で１時間脱水縮合させることによりスチレン換算分子量２００〜３８０の分子集合体を含み、液体²⁹Ｓｉ-NMRの測定による各構造の含有率をケミカルシフト−４７ppmが６.３％，−５６ppmが２１.３％，−６５ppmが８.５％，−１１０ppmが６４.０％となるように調整したシリカ系バインダを使用する以外、製造例１と同じ条件下でプライマ層，トップ層を形成した。
【００３１】
〔塗装金属板の製造例４：比較例〕
ｐＨ３.０，反応温度８０℃で７２時間脱水縮合させることにより、スチレン換算分子量３００以上の分子集合体からなり、液体^２９Ｓｉ−ＮＭＲの測定による各構造の含有率をケミカルシフト−４７ppmが０％（含まず），−５６ppmが１５％未満となるように構造制御したシリカ系バインダを使用する以外、製造例１と同じ条件下でプライマ層，トップ層を形成した。
使用したプライマ塗料を表１に、トップ塗料を表２にそれぞれ示す。
【００３２】

【００３３】

【００３４】
得られた各塗装金属板から試験片を切り出し、耐汚染性試験，ＮＯx分解試験，耐久性試験，耐摩耗性試験に供した。
耐汚染性試験では、塗装金属板に雨筋が垂れるように波板を取り付けた塗装金属板を地面から直角に起立させて取り付け、塗装金属板の明度を取付け直後及び三ヶ月経過後に測定した。そして、明度差ΔＬが±１以内に収まっている塗装金属板を○，±１を超える明度差ΔＬが生じた塗装金属板を×として耐汚染性を評価した。
【００３５】
ＮＯx分解試験では、幅５０ｍｍ，長さ１００ｍｍの試験片２枚をガラス製容器に入れ、ブラックライト（ＵＶ強度：１.０ｍＷ／ｃｍ²）で照射しながら、濃度１ｐｐｍのＮＯガスを含み湿度５０％ＲＨに調節した高純度空気を流量３.０リットル／分でガラス製容器に連続的に送り込んだ。ガラス製容器のガス出側に配置したＮＯxメータで、ガラス製容器から排出されるガスのＮＯ濃度，ＮＯ₂濃度を測定した。測定値を次式に代入してＮＯx除去率を算出した。
ＮＯx除去率（％）＝[１−(Ａ₂＋Ｂ₂)／Ａ₁]×１００
ただし、Ａ₁：初期ＮＯ濃度
Ａ₂：分解後のＮＯ濃度
Ｂ₂：分解後のＮＯ₂濃度
【００３６】
耐久性試験では、６３℃のサンシャインウェザー試験を採用し、試験開始から３０００時間経過した後で基材・金属板に対する塗膜の密着状態を調査し、剥離が生じていない塗膜を○，剥離が発生した塗膜を×として耐久性を評価した。
耐摩耗性試験では、イソプロパノールを滲み込ませて５００ｇの荷重をかけたフェルトを塗膜表面に乗せ、繰返し摩耗試験機によりフェルトで塗膜表面を１０回摩擦した後、塗膜表面の６０度光沢変化を測定した。試験後の光沢が試験前塗膜の光沢に比較して２００％以下に収まっている塗膜を○，２００％を超える光沢を示した塗膜を×として耐摩耗性を評価した。
【００３７】
表３の調査結果にみられるように、分子集合体の分子量，構造を適正管理したシリカ系バインダを用いてプライマ層，トップ層を形成した塗装金属板では、厚塗り塗装しても塗膜剥離せず、優れた光触媒活性，耐摩耗性を呈する塗膜が得られた。
形成された塗膜表面を分析したところ、スチレン換算分子量：３００以上の分子集合体からなり、液体^２９Ｓｉ−ＮＭＲの測定による各構造の含有率をケミカルシフト−４７ppmが２.０％，−５６ppmが１７.７％，−６５ppmが１７.３％，−１１０ppmが６３.０％となるように調整したシリカ系バインダを使用すると、ＩＲ分析で式(１)の高さ比率Ａが１.０５〜１.２５の範囲にあり、固体^２９Ｓｉ−ＮＭＲの測定で構造解析するとケミカルシフト−４６ppmが０〜２％，−５６ppmが２０〜２５％，−６４ppmが３５〜４５％，−９４ppmが０〜５％，−１０１ppmが５〜１０％，残りが−１１０ppmの光触媒塗膜が形成された。得られた光触媒塗装金属板は、サンシャインウェザー試験による耐久性評価で塗膜剥離が検出されず、耐摩耗性も良好であった。
【００３８】
他方、スチレン換算分子量３００未満の分子集合体をも含み、ケミカルシフト−４７ppm，−５６ppmの含有率が高いバインダを使用して形成された塗膜では、サンシャインウェザー試験で塗膜剥離が発生した。分子集合体の分子量が３００以上であっても−５６ppmの含有率が低いシリカ系バインダを用いた塗膜では、塗膜剥離を抑制できるものの耐摩耗性が低下した。
この対比から明らかなように、分子集合体の分子量，構造を適正管理したシリカ系バインダを用いてプライマ層，トップ層を形成するとき、塗膜剥離に至らず応力緩和に有効な塗膜となり、塗料焼成時や使用時の熱履歴によって導入される熱応力で引き起こされる塗膜剥離が抑制されることが確認される。しかも、硬化反応に作用するＯＨ基が調整されているので、緻密で耐摩耗性にも優れた塗膜が得られる。
【００３９】

【００４０】
更に、プライマ層：２５μｍ，トップ層：１０μｍの二層塗膜について、塗膜の構造が耐塗膜剥離性，耐摩耗性に及ぼす影響を調査した。
表４の調査結果から明らかなように、式(１)で表される高さの比率Ａが１.０５〜１.２５の範囲にあり、固体²⁹Ｓｉ−NMRの測定でケミカルシフト−４６ppmが０〜２％，−５６ppmが２０〜２５％，−６４ppmが３５〜４５％，−９４ppmが０〜５％，−１０１ppmが５〜１０％，残りが−１１０ppmとなるように制御することによって、応力分散により塗膜剥離が抑制され、耐摩耗性に優れた緻密な塗膜になることが確認された。
【００４１】

【００４２】
【発明の効果】
以上に説明したように、プライマ塗料，トップ塗料に配合するシリカ系バインダの分子量，構造を適正管理することにより，応力緩和で塗膜剥離が防止され、耐摩耗性，緻密化共に優れた光触媒塗膜が形成される。そのため、塗装原板に無機塗膜を直接形成する２コート仕様においても、優れた耐剥離性，耐塗膜剥離性が維持される。得られた光触媒塗装金属板は、長期にわたって清浄表面を維持するセルフクリーニング作用に併せ、紫外線照射や雨水に曝される環境下でも優れた耐剥離性，耐久性を呈するので、長寿命が要求される外装建材，外置き式家電機器筐体等に使用される。[0001]
[Industrial application fields]
The present invention relates to a coated metal plate that maintains a clean surface over a long period of time even in an outdoor environment exposed to rainwater or ultraviolet irradiation, and a method for manufacturing the same.
[0002]
[Prior art]
Photocatalysts such as TiO ₂ are activated by ultraviolet irradiation and exhibit an action of decomposing organic substances, NOx, SOx and the like. Utilizing the photocatalytic action of a photocatalyst, for example, providing a self-cleaning action by providing a coating film containing anatase-type titania powder on the surface of a substrate / metal plate has been studied.
When an organic substance is used as a base coating film of this type of coated metal plate, the organic coating film is decomposed by active oxygen such as O ₂ ⁻ and OH radicals generated by the photocatalytic reaction. The decomposition of the organic coating film becomes a choking phenomenon and leads to peeling of the coating film. The decomposition of the coating film due to the photocatalytic reaction can be eliminated by using an inorganic substance as the base resin (see JP-A-7-113272, JP-A-8-164334, WO96 / 29375, etc.).
[0003]
[Problems to be solved by the invention]
Although the inorganic coating film with photocatalytic activity by adding TiO ₂ has excellent weather resistance, a crack occurs in the process of forming the inorganic coating film on the substrate surface and the coating film is peeled off. In many cases, the coating film peels off due to distortion caused by heat change after installation outdoors.
As measures for preventing coating film peeling, a method of interposing an organic primer layer such as epoxy between the base material / metal plate and the inorganic coating film, a method of blending an organic substance into the inorganic coating film, and the like are employed. However, the 3-coat method not only increases the production cost, but also the photocatalyst contained in the top layer may decompose the organic primer layer. In the method of blending an organic substance with an inorganic coating film, the choking phenomenon is still unavoidable, and the weather resistance of the coating film tends to decrease.
[0004]
[Means for Solving the Problems]
The present invention has been devised to solve such problems, and by appropriately managing the molecular weight and coating film structure of the silica-based binder that forms the inorganic coating film, the stress that causes coating film peeling. Providing a photocatalyst-coated metal plate that has excellent wear resistance and photocatalytic activity, even in the 2-coat specification, in which an inorganic coating film is directly formed on a substrate / metal plate. With the goal.
[0005]
In the photocatalyst-coated metal plate of the present invention, a primer layer containing an inorganic pigment and a top layer containing a photocatalyst and an inorganic pigment are sequentially formed on the surface of the substrate, and the primer layer and the top layer are molecular assemblies having a styrene equivalent molecular weight of 300 or more. The surface layer portion of the top layer is controlled so that the ratio A of the absorbance peak height calculated by the formula (1) is in the range of 1.05-1.25, including the silica-based binder. It is characterized by that.
Height ratio A = (of 1020 cm ^-1 peak height / 1090 cm ^-1 peak height) (1)
The surface layer of the top layer has a chemical shift of -46 ppm of 0 to 2% or less, -56 ppm of 20 to 25%, -64 ppm of 35 to 45%, -94 ppm of 0 to 5% as measured by solid ²⁹ Si-NMR,- The structure is controlled so that 101 ppm is 5 to 10% and the rest is -110 ppm.
[0006]
This photocatalyst-coated metal plate is formed by applying a primer coating containing a silica-based binder having a styrene conversion molecular weight of 300 or more and an inorganic pigment-dispersed toner to a coating original plate to form a primer layer, and then a silica-based binder having a styrene conversion molecular weight of 300 or more. , A top coating containing a silane-treated photocatalyst powder and an inorganic pigment-dispersed toner is applied and baked at 150 to 400 ° C. for 5 to 30 minutes.
[0007]
As silica-based binder, silica having a solid content ratio of 40 to 70% by mass, and 30 to 70% by mass of organohydroxysilane and a partial condensate of organohydroxysilane are dispersed and dissolved in a mixed solution of water / isopropanol / ethylene glycol monobutyl ether. Liquid ²⁹ Si-NMR is measured such that the chemical shift is −47 ppm is 3% or less, −56 ppm is 15 to 25%, −65 ppm is 15 to 25%, and the remainder is −110 ppm.
[0008]
[Action]
When a photocatalyst such as titania is irradiated with ultraviolet rays, a reaction that decomposes organic matter, SOx, NOx, etc. occurs. In the decomposition reaction, the electrons in the valence band of the photocatalyst absorb energy and are excited by the conductor by ultraviolet irradiation, generating holes in the valence band, and organic matter, NOx, SOx, etc. by the strong oxidizing power of the holes Is considered to undergo oxidative degradation. Even if it is an inorganic coating film in which organic substances are introduced to prevent peeling of the coating film, the organic substances in the coating film are decomposed by photocatalytic activity, so it is difficult to achieve both durability and peeling resistance of the coating film. is there.
[0009]
In the course of studying a method of forming a coating film that avoids decomposition of organic substances due to photocatalytic activity, has no choking, is excellent in peel resistance, and does not deteriorate in photocatalytic activity, the molecular assembly of styrene equivalent molecular weight: 300 or more When a silica-based binder containing body is used for the primer layer and the top layer, fine cracks effective for stress relaxation of the coating film are generated, and even with a thick inorganic coating film, the coating film does not peel off and has excellent photocatalytic activity. It was found to be present (Japanese Patent Application No. 2002-376640).
[0010]
Although fine cracks are effective in suppressing coating film peeling, depending on the amount of generation, the abrasion resistance may be inferior, so both coating film peeling resistance and wear resistance must be achieved without reducing photocatalytic activity. In the process of developing a coating film having such film properties, it has been found that when the coating film structure is also controlled, both the peel resistance and abrasion resistance are stabilized at a high level without a decrease in photocatalytic activity. The influence of the coating film structure on the coating film peel resistance and wear resistance is presumed as follows.
[0011]
Since an inorganic coating film does not stretch itself, a large thickness of a coating film or a coating film thermally changed during outdoor use generates large cracks and is easily peeled off from a substrate or a metal plate. The coating film peeling at the time of coating film formation is considered to be due to thermal stress caused by a different thermal expansion coefficient between the substrate / metal plate and the coating film when the coating is baked. The coating film peeling during outdoor use is also considered to be caused by the stress caused by the thermal change.
[0012]
On the premise that thermal stress is the cause of coating film peeling, when the thermal stress is uniformly dispersed in the coating film without concentrating it locally, the stress falls below the adhesion at the substrate / metal plate / coating film interface. It is assumed that peeling does not occur. For example, if fine cracks effective for stress relaxation of the coating film are generated at the time of coating film formation, it is possible to prevent coating film peeling due to the occurrence of large cracks due to thermal changes that occur during thick film formation or during outdoor use . However, since fine cracks at the time of coating film formation are not preferable for the abrasion resistance of the coating film, by minimizing the fine cracks generated at the time of coating film formation and further suppressing the progress of the curing reaction during outdoor use. It is desirable to prevent an increase in stress.
[0013]
Therefore, as a result of studying a coating film structure effective for suppressing fine cracks and curing reaction during use, the present inventors have obtained an equation (1) obtained by diffracting the coating film by infrared absorption spectrum. It was elucidated that the coating film structure in which the ratio A of the height of the absorbance peak represented was controlled in the range of 1.05 to 1.25 was effective.
Height ratio A = (of 1020 cm ^-1 peak height / 1090 cm ^-1 peak height) (1)
Also, as measured by solid ²⁹ Si-NMR, chemical shift -46 ppm is 0 to 2%, -56 ppm is 20 to 25%, -64 ppm is 35 to 45%, -94 ppm is 0 to 5%, -101 ppm is 5 to 5%. It was found that when the surface layer of the top layer was tempered to 10% and the remainder to -110 ppm, both the peel resistance and abrasion resistance were further improved.
[0014]
The peak appearing at 1020 cm ⁻¹ in the infrared absorption spectrum corresponds to Si—O—Si and Si—OH, and the peak appearing at 1090 cm ⁻¹ is considered to correspond to Si—O—Si. Considering that the curing reaction at the time of coating film formation is a dehydration condensation reaction of Si—OH, a small amount of Si—OH means that there are few reactive points and a weak bonding force, and that a large amount of Si—OH is a reaction. This means that the reaction with time progresses further although there are many points and the bonding strength is strong.
[0015]
When the height ratio A represented by the formula (1) is less than 1.05, Si—OH is small and fine cracks are formed. As a result, although the stress of the coating film is reduced, the wear resistance is reduced. Conversely, when the height ratio A exceeds 1.25, there are many Si-OH, and cracks do not occur during coating film formation, but there are large cracks that cause the coating reaction to peel off during outdoor use. Likely to happen.
[0016]
The relationship between the height ratio A and the occurrence of cracks, resistance to peeling of the coating film, and abrasion resistance is also supported from the measurement results of solid ²⁹ Si-NMR. Chemical shift The peak at -46 ppm corresponds to a structure in which two alkoxy groups or OH groups are bonded to Si derived from organoalkoxysilane, and the peak at -56 ppm is a bond of one alkoxy group or OH group to Si derived from organoalkoxysilane. It corresponds to the structure. Therefore, by regulating the amounts of the peaks at -46 ppm and -56 ppm, it is possible to achieve both the peel resistance and the wear resistance. Specifically, if the amount of the -56 ppm peak is too small, the abrasion resistance is inferior, and if the amount of the -46 ppm and -56 ppm peaks is too large, the film peeling resistance is inferior. The peak amount is adjusted to the range of 0 to 2% and 20 to 25%.
[0017]
Embodiment
In the photocatalyst-coated metal plate of the present invention, a primer layer and a top layer are sequentially laminated on a base material / metal plate.
[Base material / Metal plate]
The coating original plate used for the substrate and the metal plate includes a normal steel plate, a plated steel plate, a stainless steel plate, an aluminum plate, an aluminum alloy plate, a copper plate, a copper alloy plate, and the like. The coating original plate is subjected to pre-coating treatments such as alkali degreasing, chromate treatment, and phosphate treatment as necessary.
[0018]
[Primer layer]
Styrene-converted molecular weight prepared by liquid ²⁹ Si-NMR measurement such that chemical shift -47 ppm is 3% or less, -56 ppm is 15 to 25%, -65 ppm is 15 to 25%, and the remainder is -110 ppm. When a primer coating in which this silica-based binder is blended with an inorganic pigment-dispersed toner is applied to a substrate or a metal plate and baked, a primer layer with relaxed stress and excellent wear resistance is formed.
[0019]
Silica-based binder is a chemical shift in the measurement of liquid ²⁹ Si-NMR by dispersing the solid content of silica, organohydroxysilane and a partial condensate of organohydroxysilane in a mixed solvent of water / isopropanol / ethylene glycol monobutyl ether. It is prepared so that −47 ppm is 3% or less, −56 ppm is 15 to 25%, −65 ppm is 15 to 25%, and the remainder is −110 ppm. Specifically, a solid content composed of silica: 40 to 70% by mass, and a partial condensate of organohydroxysilane and organohydroxysilane: 30 to 60% by mass is dispersed in a mixed solvent of water / isopropanol / ethylene glycol monobutyl ether. If necessary, when the pH value of the silica binder is adjusted to 3 to 6.5 (preferably 4 to 5) with aqueous amine, organic amines such as triethanolamine, dimethylamino ether, etc., the silica binder Storage stability is improved.
[0020]
The organohydroxysilane is, for example, the general formula RSi (OH) ₃ [where R is an alkyl group having 1 to 3 carbon atoms, a vinyl group, a 3,4-epoxycyclohexyl group, a γ-glycidoxypropyl group, a γ-mercaptopropyl group, or A chloropropyl group]. Examples of the partial condensate of organohydroxysilane include an oligomer obtained by partial condensation of an organohydroxysilane of the general formula RSi (OH) ₃ .
[0021]
The solid content in the silica-based binder is a molecular assembly in which organohydroxysilane and a partial condensate of organohydroxysilane are combined by dehydration condensation using colloidal silica as a core. The molecular weight and structure of the molecular assembly can be controlled by the pH value during the dehydration condensation, the reaction time, the reaction temperature, and the like. The molecular assembly is styrene equivalent molecular weight: 300 or more, as measured by liquid ²⁹ Si-NMR, chemical shift −47 ppm is 3% or less, −56 ppm is 15 to 25%, −65 ppm is 15 to 25%, and the rest is −110 ppm. When the adjustment is performed, a coating film having relaxed stress and excellent wear resistance is formed. If there are too few reactive OH groups, many fine cracks are formed and the stress of the coating film is reduced, but the wear resistance is lowered. On the other hand, when the amount of OH groups is too large, cracks do not occur at the time of forming the coating film, and large cracks that cause the coating film to peel off due to the progress of the curing reaction during outdoor use. Therefore, by appropriately regulating the amount of the structure having an OH group, it is possible to achieve both the peel resistance and the wear resistance.
[0022]
The primer paint is blended with an inorganic pigment having a solid content of 10 to 80% by mass (preferably 20 to 75% by mass). Inorganic pigments include rutile titania treated with SiO ₂ , Al ₂ O ₃ or ZrO ₂ , (Co _1/2 , Ni, Zn _1/2 ) TiO ₄ , CoAl ₂ O ₄ , Cu (Cr, Mn) ₃ O ₄ and TiO ₂ —NiO—Sb ₂ O ₅ . In order to obtain sufficient concealability, an inorganic pigment of 10% by mass or more is necessary. However, when an excessive amount of inorganic pigment exceeding 80% by mass is blended, the adhesion of the primer layer to the substrate / metal plate is lowered.
[0023]
The primer paint is applied to a pre-painted substrate / metal plate, and then dried and baked in a temperature range of 60 to 350 ° C. When the drying temperature is less than 60 ° C., the primer layer is not sufficiently dried, and unevenness is likely to occur in the top layer formed on the primer layer. Conversely, when the heating temperature exceeds 350 ° C., a large crack is generated in the primer layer, and the primer layer is easily peeled off from the substrate / metal plate.
[0024]
[Top layer]
By baking the top coating applied to the primer layer, a top layer excellent in stain resistance and coating film adhesion is formed. The top coating is prepared by blending a silica-based binder similar to the primer coating with a silane-treated photocatalyst powder and an inorganic pigment dispersed toner. The silica-based binder is mixed with a photocatalyst powder having a solid content of 5% by mass or more and a total content of 10-80% by mass (preferably 20-50% by mass) with the inorganic pigment. In order to obtain a sufficient photocatalytic activity, 5% by mass or more of the photocatalyst powder is required. However, if an excessive amount of the photocatalyst powder exceeds 80% by mass, the adhesion of the top layer is lowered.
[0025]
As the photocatalyst powder, one or more selected from TiO ₂ , ZnO, WO ₃ , FeTiO ₃ , and SrTiO ₃ are used. Of these, anatase-type titania powder is preferred because it is chemically stable, has high activity, and is inexpensive.
The applied top paint is baked in a temperature range of 150 to 400 ° C. higher than the heating temperature at the time of forming the primer layer. A heating temperature of 150 ° C. or higher is necessary for sufficient condensation polymerization of the coating film. However, when heated to a high temperature exceeding 400 ° C., cracks that lead to peeling of the coating film tend to occur. Preferably, the heating temperature at the time of forming the primer layer is set to 80 to 250 ° C. and the heating temperature at the time of forming the top layer is set to 150 to 400 ° C. in order to promote drying of the coating film.
[0026]
By setting the temperature during the formation of the top layer, a strong bond is obtained between the primer layer and the top layer, and the adhesion of the top layer to the primer layer is improved by the heat treatment during the formation of the top layer. As a result, the adhesiveness with respect to a base material and a metal plate is favorable, and the coating film in which the stress is relaxed without reaching the coating film is formed. If the firing temperature is less than 150 ° C., the firing is insufficient and the wear resistance is extremely lowered. When the baking temperature exceeds 400 ° C., the shrinkage of the base material and the coating film changes extremely during the cooling process, and thus the coating film is easily peeled off.
The control of the coating film structure makes it possible to achieve both the effect of generating moderate fine cracks in the top layer to increase the photocatalytic activity and the effect of preventing a decrease in wear resistance due to the generation of many fine cracks. The photocatalyst-coated metal sheet obtained in this way is used for exterior building materials, exterior-type home appliance housings, etc. that are exposed to ultraviolet irradiation and rainwater for a long period of time, utilizing excellent pollution resistance and air purification capability. Is done.
[0027]
【Example】
[Production Example of Painted Metal Plate 1: Example of the Invention]
A SUS304 stainless steel plate having a thickness of 1.0 mm was used as a coating original plate, and was subjected to alkaline degreasing, pickling, water washing and drying.
The primer coating was prepared by blending an inorganic pigment-dispersed toner in which rutile-type titanium oxide (white pigment) surface-treated with zirconia was dispersed in a mixed solvent of water / isopropanol / ethylene glycol monobutyl ether and a silica-based binder. . The primer coating was applied to the coating original plate and baked at 140 ° C. for 20 minutes to form a primer layer having a dry film thickness of 25 μm.
[0028]
The top coating was prepared by dispersing anatase titania powder having a particle diameter of 20 nm in a mixed solvent of water / isopropanol / ethylene glycol monobutyl ether in the same silica-based binder and inorganic pigment dispersed toner as the primer coating. A top coating was applied on the primer layer and baked at 200 ° C. for 20 minutes to form a top layer having a dry film thickness of 10 μm. When the silica binder is measured by liquid ²⁹ Si-NMR, the content of each structure is as follows: chemical shift -47 ppm is 2.0%, -56 ppm is 17.7%, -65 ppm is 17.3%, -110 ppm. Was 63.1%.
[0029]
[Production Example 2 of Painted Metal Plate: Example of the Invention]
A primer layer and a top layer were formed under the same conditions as in Production Example 1 except that an aluminum plate having a thickness of 2.5 mm was used as a coating original plate and anatase-type titania powder having a particle diameter of 7 nm was used.
[0030]
[Production Example 3 of Painted Metal Plate: Comparative Example]
By dehydrating and condensing at a reaction temperature of 80 ° C. for 1 hour, the content of each structure containing molecular aggregates having a molecular weight of 200 to 380 in terms of styrene was measured by liquid ²⁹ Si-NMR, and the chemical shift −47 ppm was 6.3%, − The primer layer and the top layer were formed under the same conditions as in Production Example 1 except that a silica-based binder adjusted so that 56 ppm was 21.3%, -65 ppm was 8.5%, and -110 ppm was 64.0%. Formed.
[0031]
[Production Example 4 of Painted Metal Plate: Comparative Example]
pH 3.0, by engaged 72 hours dehydration condensation at a reaction temperature of 80 ° C., consists styrene equivalent molecular weight of 300 or more molecular assembly, the liquid ²⁹ Si-NMR measurement chemical shift -47ppm the content of each structure according to the 0% (Not included) A primer layer and a top layer were formed under the same conditions as in Production Example 1 except that a silica-based binder whose structure was controlled so that −56 ppm was less than 15% was used.
Table 1 shows the primer paints used and Table 2 shows the top paints.
[0032]

[0033]

[0034]
A test piece was cut out from each of the obtained coated metal plates and subjected to a contamination resistance test, a NOx decomposition test, a durability test, and an abrasion resistance test.
In the contamination resistance test, a painted metal plate with corrugated plates attached so that rain stripes hang on the painted metal plate was installed upright at a right angle from the ground, and the brightness of the painted metal plate was measured immediately after installation and after three months. Then, the resistance to contamination was evaluated by ◯ for a coated metal plate having a brightness difference ΔL within ± 1, and x for a coated metal plate having a brightness difference ΔL exceeding ± 1.
[0035]
In the NOx decomposition test, two test pieces having a width of 50 mm and a length of 100 mm are put in a glass container and irradiated with a black light (UV intensity: 1.0 mW / cm ² ) while containing NO gas with a concentration of 1 ppm and a humidity of 50 High-purity air adjusted to% RH was continuously fed into a glass container at a flow rate of 3.0 liters / minute. The NOx meter and NO ₂ concentration of the gas discharged from the glass container were measured with a NOx meter arranged on the gas outlet side of the glass container. The measured value was substituted into the following equation to calculate the NOx removal rate.
NOx removal rate (%) = [1− (A ₂ + B ₂ ) / A ₁ ] × 100
However, A ₁ : Initial NO concentration A ₂ : NO concentration after decomposition B ₂ : NO ₂ concentration after decomposition
In the durability test, a sunshine weather test at 63 ° C. was adopted, and after 3000 hours from the start of the test, the adhesion state of the coating film to the base material / metal plate was investigated, and the coating film in which peeling did not occur was peeled off. Durability was evaluated with x being a coating film on which the occurrence occurred.
In the abrasion resistance test, felt felt impregnated with isopropanol and subjected to a load of 500 g was placed on the surface of the coating, and the coating surface was rubbed 10 times with felt using a repeated abrasion tester. Changes were measured. Abrasion resistance was evaluated with a coating film in which the gloss after the test was within 200% or less compared to the gloss of the coating film before the test, and a coating film showing a gloss exceeding 200% as x.
[0037]
As can be seen from the survey results in Table 3, the coated metal sheet with a primer layer and top layer formed using a silica-based binder with proper control of the molecular weight and structure of the molecular assembly can be peeled off even when thickly coated. Thus, a coating film having excellent photocatalytic activity and wear resistance was obtained.
Analysis of the formed coating film surface, a molecular weight in terms of styrene: 300 made from the above molecular assembly, chemical shift -47ppm the content of the structure by measuring the liquid ²⁹ Si-NMR is 2.0%, - 56 ppm Is 17.7%, -65 ppm is 17.3%, -110 ppm is 63.0%, and a silica-based binder is used, the height ratio A of formula (1) is 1.05 in IR analysis. It is in the range of ˜1.25 and structural analysis by solid ²⁹ Si-NMR measurement shows chemical shift of −46 ppm 0 to 2%, −56 ppm 20 to 25%, −64 ppm 35 to 45%, −94 ppm 0 A photocatalytic coating film of -5%, -101 ppm was 5-10%, and the remaining was -110 ppm was formed. The obtained photocatalyst-coated metal plate had good wear resistance because no coating film peeling was detected in the durability evaluation by the sunshine weather test.
[0038]
On the other hand, in the coating film formed using a binder containing a molecular assembly having a molecular weight of less than 300 in terms of styrene and having a high chemical shift of −47 ppm and −56 ppm, the coating film peeled off in the sunshine weather test. Even when the molecular weight of the molecular assembly is 300 or more, the coating using the silica-based binder having a low content of −56 ppm can suppress the peeling of the coating, but the wear resistance is lowered.
As is clear from this comparison, when the primer layer and the top layer are formed using a silica-based binder in which the molecular weight and structure of the molecular assembly are appropriately controlled, the coating film is effective for stress relaxation without causing coating film peeling. It is confirmed that the coating film peeling caused by the thermal stress introduced by the thermal history at the time of baking or use of the paint is suppressed. Moreover, since the OH group that acts on the curing reaction is adjusted, a dense coating film with excellent wear resistance can be obtained.
[0039]

[0040]
Further, the effects of the coating film structure on the peeling resistance and abrasion resistance of the two-layer coating film of primer layer: 25 μm and top layer: 10 μm were investigated.
As is clear from the investigation results in Table 4, the height ratio A represented by the formula (1) is in the range of 1.05 to 1.25, and the chemical shift of -46 ppm is found by measurement of solid ²⁹ Si-NMR. By controlling so that 0-2%, -56ppm is 20-25%, -64ppm is 35-45%, -94ppm is 0-5%, -101ppm is 5-10%, and the rest is -110ppm, It was confirmed that peeling of the coating film was suppressed by the stress dispersion, and a dense coating film having excellent wear resistance was obtained.
[0041]

[0042]
【The invention's effect】
As explained above, by properly managing the molecular weight and structure of the silica-based binder blended in the primer paint and top paint, the photocatalyst coating with excellent wear resistance and densification can be prevented by stress relaxation to prevent peeling of the coating film. A film is formed. Therefore, even in the 2-coat specification in which the inorganic coating film is directly formed on the coating original plate, excellent peeling resistance and coating film peeling resistance are maintained. The resulting photocatalyst-coated metal sheet is required to have a long service life because it exhibits excellent peeling resistance and durability even in environments exposed to ultraviolet rays and rainwater, in addition to a self-cleaning action that maintains a clean surface over a long period of time. It is used for exterior building materials and external home appliance housings.

Claims

A primer layer containing an inorganic pigment, a top layer containing a photocatalyst and an inorganic pigment are sequentially formed on the surface of the substrate, and the primer layer and the top layer contain a silica-based binder composed of a molecular aggregate having a styrene conversion molecular weight of 300 or more, The surface layer of the top layer
The absorbance peak height ratio A calculated by the following formula (1) is in the range of 1.05-1.25,
As measured by solid ²⁹ Si-NMR, chemical shift -46 ppm is 0 to 2%, -56 ppm is 20 to 25%, -64 ppm is 35 to 45%, -94 ppm is 0 to 5%, -101 ppm is 5 to 10%, As the rest is -110 ppm,
A photocatalyst-coated metal plate with excellent wear resistance, contamination resistance, and coating adhesion, characterized by a controlled structure.
(Formula 1)
Height ratio A = (1020cm ^-1 peak height / 1090 cm ^-1 peak height)

Styrene-converted molecular weight: 300 or more molecules conditioned by liquid ²⁹ Si-NMR, chemical shift -47 ppm 3% or less, -56 ppm 15-25%, -65 ppm 15-25%, the rest -110 ppm After applying a primer coating containing an aggregated silica-based binder and an inorganic pigment-dispersed toner to a coating original plate to form a primer layer, a chemical shift of -47 ppm is 3% or less and -56 ppm is 15 to 15 in liquid ²⁹ Si-NMR. Styrene-converted molecular weight tempered to 25%, -65 ppm is 15-25%, and the remainder is -110 ppm: a top coating containing a silica-based binder comprising a molecular aggregate of 300 or more, a silane-treated photocatalyst powder, and an inorganic pigment-dispersed toner Photocatalyst coating with excellent wear resistance, contamination resistance, and coating film adhesion, characterized in that it is baked at 150 to 400 ° C. for 5 to 30 minutes Manufacturing method of a metal plate.

A silica-based binder in which silica having a solid content ratio of 40 to 70% by mass and 30 to 70% by mass of organohydroxysilane and a partial condensate of organohydroxysilane are dispersed and dissolved in a mixed solution of water / isopropanol / ethylene glycol monobutyl ether. The manufacturing method of Claim 2 used.