JP2004204091A - Photocatalyst coating composition - Google Patents
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【０００１】
【産業上の利用分野】
本発明は、光触媒反応によるセルフクリーニング作用で清浄表面が長期間にわたり維持され、密着性に優れた塗膜の形成に適した光触媒塗料組成物に関する。
【０００２】
【従来の技術】
塗膜に光触媒粒子を分散させると、セルフクリーニング作用が塗膜表面に付与され、長期間にわたって清浄な塗膜表面が維持される。有機物ベースの塗膜は光照射で生成した活性酸素によって分解しチョーキング現象が発生するので、活性酸素による分解のない無機物をベースに光触媒塗膜を形成している。
塗膜に光触媒活性を付与する塗料組成物としては、テトラアルコキシシラン等のアルコキシドを溶解した水／エタノール混合溶媒にＴｉＯ2の水分散ゾルを分散させた系（WO96／29375），オルガノシリカゾルを有機溶媒に溶解させた溶液にＴｉＯ2粉末を分散させた系（特開平8−67835号公報），シラン処理したＴｉＯ2粉末をシリコーン樹脂に分散させた系（特開平9−227831号公報）等が報告されている。
【０００３】
酸化チタン等の光触媒粒子の結合剤として使用されているテトラアルコキシシランは、加水分解，縮合反応で架橋硬化するので硬化時の体積収縮が大きい。体積収縮は、硬化後の塗膜において非常に大きな収縮応力となり、緩和されることなく残留する。残留応力は乾燥膜厚で５μｍ以上の厚塗り塗装を施すとき塗膜剥離発生の原因となるので、残留応力に起因する欠陥を回避する薄塗り塗装が余儀なくされている。
【０００４】
薄塗り塗装は、浄化作用に必要な光触媒活性を十分に活用できないことは勿論、光触媒塗膜の性能，品質安定性でも不利である。たとえば、大面積の被塗物の表面に均一な膜厚の塗膜を形成することは困難であり、表面の僅かな凹凸や歪みを反映する部分的な厚膜化が避けられない。複雑な表面形状をもつ被塗物に塗装する場合でも、表面の凹凸を倣った厚膜部が生じやすい。厚膜部では、テトラアルコキシシランの体積収縮に起因する収縮応力の影響が現れ、塗膜剥離が発生しやすい。
オルガノシリカゾルを有機溶媒に溶解させた溶液にＴｉＯ2粉末を分散させた塗料組成物では、ＴｉＯ2の分散が不十分で凝集しやすいため、作製された塗膜が不均一になりがちで膜厚制御も難しい。ＴｉＯ2粉末の分散性を向上させるためにシラン処理したＴｉＯ2粉末をシリコーン樹脂に分散させた塗料組成物を使用すると、厚膜化が可能であるが、塗膜に含まれる有機成分が多くなり、光触媒粒子による分解でチョーキングしやすい塗膜になる。
【０００５】
【発明が解決しようとする課題】
そこで、本発明者等は、バインダ成分であるオルガノアルコキシシランの一部を光触媒分散トナーに予め添加することによりアナターゼ型チタニア粉末の凝集沈殿が防止できることを紹介した（特開2002−105357号公報）。オルガノアルコキシシランはアナターゼ型チタニア粉末の表面を覆い、粉末表面のゼータ電位が無機バインダのｐＨ値から外れる。その結果、無機バインダと混合した場合でもアナターゼ型チタニア粉末の凝集沈殿が抑制されるものと推察される。
有機成分が極く僅かで主成分がコロイダルシリカの無機バインダを使用すると、チョーキングが抑えられ耐久性に優れた塗膜が形成される。塗膜に含まれる多量のコロイダルシリカは応力緩和に寄与し、シラン縮合物単体のバインダに比較して厚塗り塗装でも耐割れ性に優れた塗膜が形成される。
【０００６】
【課題を解決するための手段】
本発明は、先願・特開2002−105357号公報で紹介した光触媒塗料組成物を更に改良したものであり、光触媒塗料組成物に配合する無機バインダの分子量分布を適正管理することにより、厚塗り塗装した場合でも剥離が生じがたく、優れた清浄作用を呈する光触媒塗膜を形成することを目的とする。
【０００７】
本発明で提案する光触媒塗料組成物は、光触媒分散トナー，無機バインダを含んでいる。
光触媒分散トナーは、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ＴｉＯ2粉末，オルガノアルコキシシラン，水を配合することにより調製される。ＴｉＯ2粉末には粒径５〜２００ｎｍのアナターゼ型チタニア粉末が使用され、塗料組成物の固形分の５〜８０質量％を占める割合で配合される。オルガノアルコキシシランは、一般式Ｒ1Ｓｉ(ＯＲ2)3〔Ｒ1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、Ｒ2は炭素数１〜４のアルキル基又はアリール基〕で表され、好ましくは１〜１０質量％の割合で配合される。水添加量は、オルガノアルコキシシランを部分加水分解させるが、オルガノアルコキシシラン相互の脱水縮合反応を進行させない範囲、具体的には０.１〜１０質量％の範囲で選定される。
【０００８】
無機バインダは、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％の固形分を水／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液に分散させている。オルガノヒドロキシシランは、一般式Ｒ1Ｓｉ(ＯＨ)3〔Ｒ1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。シリカに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結合した分子集合体は、加水分解，縮合時の温度，時間を調整することにより所定の分子量分布に収められている。シリカには、コロイダルシリカ、主として水系コロイダルシリカ分散液が使用される。
【０００９】
【作用】
光触媒分散トナーに配合したオルガノアルコキシシランは、アナターゼ型チタニア粉末の表面にオルガノアルコキシシランのまま吸着し、或いは溶剤中に単に分散した状態で存在する。吸着したオルガノアルコキシシランはアナターゼ型チタニア粉末の分散性を向上させるが、長期間にわたる貯蔵では分散性が十分とはいえない。
水が存在する系では、オルガノアルコキシシランのアルコキシ基が部分加水分解する。加水分解生成物がアナターゼ型チタニア粉末表面のＯＨ基と結合し、この結合を介しアナターゼ型チタニア粉末表面にオルガノアルコキシシランが付着する。アナターゼ型チタニア粉末は、オルガノアルコキシシランの付着によって分散性が向上し、長期にわたって凝集沈殿なく光触媒分散トナー中に懸濁する。その結果、貯蔵安定性に優れた光触媒分散トナーが得られる。良好な分散性は、無機系バインダと混合した後でも維持される。
【００１０】
アナターゼ型チタニア粉末表面に対するオルガノアルコキシシランの付着量は光触媒分散トナーの水添加量で制御でき、オルガノアルコキシシラン付着による分散性の向上は０.１質量％以上の水添加量でみられる。水添加量の増加に応じてアナターゼ型チタニア粉末表面に付着するオルガノアルコキシシランが多くなり、アナターゼ型チタニア粉末の分散性が向上する。しかし、１０質量％を超える過剰量の水を添加すると、アナターゼ型チタニア粉末表面に付着するアルコキシ基の加水分解生成物が多くなりすぎ、光触媒活性が損なわれる。過剰量の水添加は、光触媒分散トナーに添加したオルガノアルコキシシラン相互の脱水縮合を促進させ、アナターゼ型チタニア粉末表面に付着する加水分解生成物の割合が却って減少する。
【００１１】
光触媒分散トナーに配合される水以外の成分は、次のように定めることが好ましい。
光触媒としては、光触媒活性が高く化学的安定性にも優れた粒径５〜２００ｎｍのアナターゼ型チタニア粉末を用い、５〜８０質量％の割合で配合する。粒径５ｎｍの粉末は製造自体が難しく、２００ｎｍを超える粒径では光触媒活性が不足する。アナターゼ型チタニア粉末の配合割合が５質量％未満になるとチクソ性がなく粒子の沈降が早く固めのケーキになるため、トナー使用時の再分散が困難になる。逆に８０質量％を超える配合量では、チクソ性が高くなりすぎ却ってトナーとしての流動性が損なわれる。
【００１２】
オルガノアルコキシシランは、一般式Ｒ1Ｓｉ(ＯＲ2)3〔Ｒ1はアルキル基，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，Ｒ2は炭素数１〜４のアルキル基又はアリール基〕で表され、１〜１０質量％の割合で配合される。オルガノアルコキシシランは、有機官能基の導入によってシラン相互の反応が抑制され、アナターゼ型チタニア粉末の表面に付着する割合が高くなる。この点、テトラアルコキシシランでは、加水分解が過度に進行してアナターゼ型チタニア粉末の表面に付着するだけでなく、シラン相互が反応する結果としてアナターゼ型チタニア粉末の分散に寄与しない割合が高くなる。
【００１３】
オルガノアルコキシシランであっても、有機官能基が２個以上になるとアナターゼ型チタニア粉末の表面に付着する有機物の量が増加する。有機物が過剰に付着したアナターゼ型チタニア粉末の分散トナーから作製された光触媒塗膜を光照射環境に置くと有機物が分解し、塗膜のチョーキングが短時間に進行する。そこで、Ｓｉに直接結合する有機官能基を一つだけとし、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にすることが好適である。
【００１４】
オルガノアルコキシシランの配合量は、１〜１０質量％の範囲に定められる。１質量％未満の配合量では分散性の向上がみられず、逆に１０質量％を超える配合量ではアナターゼ型チタニア粉末表面の被覆率が高くなりすぎて塗膜形成後の光触媒活性が極端に低下する。オルガノアルコキシシランの配合量はアナターゼ型チタニア粉末の粒径に依存する。たとえば、７ｎｍのＴｉＯ2粉末は約３００ｍ2／ｇの大きな表面積をもつので、８質量％のオルガノアルコキシシランで最も大きな効果が得られる。粒径２０ｎｍのＴｉＯ2粉末では表面積が５０ｍ2／ｇ程度であり、オルガノアルコキシシランの配合量３質量％で最も効果的になる。
【００１５】
溶媒には、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が使用される。混合比率は、イソプロパノール：４０〜６０質量％，エチレングリコールモノブチルエーテル：４０〜６０質量％が好ましい。混合比率の調整によって，アナターゼ型チタニア粉末の分散性が改善されると共に、光触媒分散トナーをバインダと混合した後で塗膜を形成する際に揮発スピードが適度にコントロールされるので、剥離に至るクラックの発生が防止される。
光触媒分散トナーは、オルガノアルコキシシラン，水を添加したイソプロパノール／エチレングリコールモノブチルエーテルの混合溶媒にアナターゼ型チタニア粉末を加え、攪拌機で攪拌した後、充填したビーズが攪拌状態に維持されている横型ミルに流量１リットル／分の速さで注入することにより調製される。必要に応じ、顔料，染料等の着色剤や増粘剤等の添加材を添加する。
【００１６】
無機バインダは、シリカ，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固形分として水／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させることにより調製される。コロイダルシリカには、水系コロイダルシリカ分散液とイソプロパノール系コロイダルシリカ分散液の混合物が好ましい。シリカの平均粒径は１５０ｎｍ以下（更には、３０ｎｍ）以下が好ましく、無機バインダの保存安定性を確保する上で好ましくは酸性のコロイダルシリカが使用される。
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は、オルガノアルコキシシランの加水分解によって得られ、一般式Ｒ1Ｓｉ(ＯＨ)3で表される。代表的なオルガノアルコキシシランには、光触媒分散トナーの一成分と同じ化合物Ｒ1Ｓｉ(ＯＲ2)3を使用できる。オルガノヒドロキシシランの部分縮合物には、一般式Ｒ1Ｓｉ(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り得られるオリゴマー等も使用できる。
【００１７】
無機バインダの固形分は、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。無機バインダを光触媒分散トナーと混合すると，オルガノヒドロキシシランの部分縮合物が付着したアナターゼ型チタニア粉末とコロイダルシリカを核として分子集合体が反応・結合するため、強固なネットワークが形成されると共に、アナターゼ型チタニア粉末が塗膜に均一分散される。
コロイダルシリカに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結合した分子集合体は、重合時の反応時間，反応温度を制御することにより所定の分子量，分子量分布に収められる。分子量が３００以上で、分子量３００〜５００が０〜２０％，分子量５００〜１０００が２０〜４０％，分子量１０００〜１００００が４０〜７０％の分子量分布に調整することにより、形成された塗膜の耐剥離性が向上する。
【００１８】
分子量分布が耐剥離性に及ぼす影響は、次のように考えられ、後述の実施例によっても支持される。低分子量成分を含む塗料組成物から作製された塗膜では、低分子量成分のＯＨ基が反応点となって塗膜に大きな応力を加え、完全に加水分解が完了していない分子が単独で存在し、コロイダルシリカとの結合が生じていない（図１ａ）。そのため、塗膜形成時に反応点が多く、脱水縮合反応が急激に進行し、結果として大きな応力が塗膜に残留する。しかも、低分子量成分（未反応成分）は塗膜ｐの表層にブリードしやすく、雨水や紫外線照射UVに曝される環境下で硬化反応が生起する。硬化反応の結果、体積収縮に起因する収縮応力が塗膜ｐに発生し、基材ｂに達する亀裂ｃが生じる（図１ｂ）。
【００１９】
他方、完全にアルコキシドの加水分解が完了した成分を含む塗料組成物から作製された塗膜では、アルコキシドとコロイダルシリカとの結合が十分に進み、コロイダルシリカを取り囲んだ大きな分子となっている。そのため、反応点が少なく、塗膜形成時に反応が徐々に進行するため残留応力も小さくなる（図２ａ）。しかも、塗膜表面に未反応成分のブリードがなく、塗膜内部に微細なクラックfcが入っている。そのため、雨水や紫外線照射に曝される環境下で硬化反応が進行することなく、塗膜に加えられる応力があっても微細クラックによって分散されるため、基材に達するクラックにまで成長しない（図２ｂ）。
【００２０】
加水分解及び脱水縮合反応による結合状態は、ゲル濾過クロマトグラフィで測定し、ポリスチレンを標準物質として作成した検量線から算出した分子量で評価できる。具体的には、無機バインダとテトラヒドロフランで２０倍希釈し、１μｍフィルタで濾過した後、カラムに1000／2000 Shoudex 801，802を用いたゲル濾過クロマトグラフィ（HLC 8020：東ソー株式会社製）を使用し、テトラヒドロフランを測定溶媒としＲＩ検出器により分子量分布を求めた。縮合が分子量３００以上に進行し、３００未満の低分子量成分がなくなると、過剰なＯＨ基や塗膜表面にブリードする低分子量成分の影響が抑制される。なかでも、分子量３００〜５００が０〜２０％，分子量５００〜１０００が２０〜４０％，分子量１０００〜１００００が４０〜７０％の分子量分布に管理されているとき、低分子量成分の影響抑制が効果的になる。
【００２１】
溶媒は、コロイダルシリカ分散液中の水分，オルガノヒドロキシシランの縮合水，オルガノヒドロキシシランの加水分解で生じるアルコール，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から構成される。無機バインダの溶媒として少なくとも２０質量％のエチレングリコールモノブチルエーテルを配合すると、無機バインダの保存安定性が飛躍的に向上し、塗装作業性，成膜性に優れた塗料組成物が得られる。従来の無機バインダでは２０質量％以上の水分を含ませると保存安定性が劣化するが、２０質量％以上のエチレングリコールモノブチルエーテルを含む系では、２０質量％以上の水分を含んでいても十分な保存安定性が維持される。無機バインダは、保存安定性を向上させるため、アンモニア水，トリエタノールアミン，ジメチルエタノールアミン等の有機アミン類を用いてｐＨ：４〜５に調整することが好ましい。
【００２２】
光触媒分散トナーは、オルガノアルコキシシラン，水を添加したイソプロパノール／エチレングリコールモノブチルエーテルの混合溶媒にアナターゼ型チタニア粉末を加え、攪拌機で攪拌した後、充填したビーズが攪拌状態に維持されている横型ミルに流量１リットル／分の速さで注入することにより調製される。必要に応じ、顔料，染料等の着色剤や増粘剤等の添加材を添加することも可能である。
無機バインダは、コロイダルシリカ分散液に添加したオルガノアルコキシシランを加水分解させ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とした後、溶剤で希釈する方法、コロイダルシリカ分散液を溶剤で希釈した後、オルガノアルコキシシランを添加して加水分解させる方法等によって調製される。コロイダルシリカにオルガノアルコキシシランを添加して加水分解させるとき、液温を１０〜８０℃に保ち、常圧下で１〜２４時間攪拌しながら反応させる。非水性コロイダルシリカ分散液の一部を後で添加し、更に加熱・反応させても良い。オルガノアルコキシシランの加水分解に際しては、無機酸，有機酸等の加水分解触媒を少量添加することもできる。
【００２３】
十分に攪拌した光触媒分散トナーに無機バインダを徐々に加えながら、更に攪拌することにより光触媒塗料組成物が調製される。このとき、固形分としてＴｉＯ2が５〜８０質量％となる配合比率で光触媒分散トナー，無機系バインダを混合する。十分な光触媒活性を得る上で５質量％以上のＴｉＯ2含有量が必要であるが、８０質量％を超える過剰量のＴｉＯ2が含まれると塗膜の密着性が低下する。
調製された塗料は、スプレー法，浸漬法，フローコーティング法，ロールコート法，スクリーン印刷法，静電塗装法等によって、前処理された基材に塗布される。塗布後、８０〜１３０℃で１〜３０分加熱することにより、基材に対する密着性に優れた塗膜が形成される。塗膜の厚さは、基材の種類や用途に応じて異なるため一概に定めることはできないが、通常１〜３０μｍの範囲で調整される。光触媒塗料組成物が塗布される基材には、普通鋼，めっき鋼板，ステンレス鋼板，アルミニウム，銅、真鍮等の金属や、セメント，コンクリート，タイル，スレート板，ガラス，石材等がある。加熱時の温度によっては、プラスチック等の有機材料にも塗装可能である。
【００２４】
【実施例】
アナターゼ型チタニア粉末分散トナーの調製
イソプロパノール：５０質量％，エチレングリコールモノブチルエーテル：５０質量％の混合溶媒に３質量％のオルガノアルコキシシラン，０.３質量％の水を添加し、更に粒径２０ｎｍのアナターゼ型チタニア粉末を添加した。アナターゼ型チタニア粉末の添加量は、塗料全体の４０質量％となる割合に設定した。ビーズミルを用いた攪拌機で混合物を分散させることにより光触媒分散トナーを調製した。
【００２５】
無機系バインダの調製
水系コロイダルシリカ：２１.２ｇ（平均粒径５〜２０ｎｍ，固形分２０質量％，ｐＨ３.０）とイソプロパノール系コロイダルシリカ６２.６ｇ（平均粒径５〜２０ｎｍ，固形分２０質量％）を混合した後、メチルトリメトキシシラン１３.９ｇを加え、８０℃で１２時間攪拌して加水分解を完了させた。次いで、加水分解物にイソプロパノール：３３質量％，エチレングリコールモノブチルエーテル：６７質量％の混合溶媒を添加し、更にアンモニア水を添加してｐＨを４.５に調整した。
得られた光触媒分散トナー，無機系バインダを固形分中のＴｉＯ2含有量が４０質量％となる割合で混合攪拌し、５０μｍのメッシュを用いて濾過し塗料化した。
【００２６】
前処理したSUS304ステンレス鋼基材に塗料をスプレー塗布し、２００℃で２０分加熱することにより膜厚１０μｍの塗膜を形成した。比較のため、水無添加の光触媒分散トナーを無機系バインダと混合することにより調製された塗料（比較例１）及び反応時間の調整により分子量３００未満とした無機バインダを光触媒分散トナーと混合した塗料（比較例２）を用いて同様にSUS304ステンレス鋼基材を塗装した。
【００２７】
調製された光触媒塗料組成物の分散性及び塗膜の耐剥離性，光触媒活性を以下の方法で評価した。
(１)光触媒塗料組成物の分散性
光触媒分散トナー，無機系バインダを混合した塗料化した後、１日経過後にＴｉＯ2粒子の凝集状態を調査した。５μｍ以上のツブが検出されない塗料組成物を○，１０μｍ以上のツブはないが５〜１０μｍのツブが検出された塗料組成物を△，１０μｍ以上のツブが生じた塗料組成物を×として分散性を評価した。
【００２８】
(２)塗膜の耐剥離性
６３℃のサンシャインウェザー試験で塗膜の耐剥離性を調査し、試験開始から３０００時間経過した時点で剥離が検出されなかった塗膜を○，剥離した塗膜を×として耐剥離性を評価した。
(３)塗膜の光触媒活性
付着量０.２ｍｇ／ｃｍ2でサラダ油を試験片表面に付着させ、５ｍＷ／ｃｍ2のブラックライトで２４時間照射した後、試験片に残存しているサラダ油の重量を測定し、重量減少率を油分解率として光触媒活性を評価した。
【００２９】
表１の調査結果にみられるように、オルガノアルコキシシラン，水を添加した光触媒分散トナーから得られた塗料組成物では、無機バインダの分子量分布に拘らず良好な分散性を示した。他方、水無添加の光触媒分散トナーを用いた塗料組成物（比較例11）では、５〜１０μｍのツブが検出された。
【００３０】
表１の各種塗料組成物を前処理したSUS304ステンレス鋼基材にスプレー塗布し、塗布量によって膜厚を調整した塗膜を形成した。得られた塗膜の耐剥離性，光触媒活性を調査した結果を表２に示す。
表２から明らかなように、分子量３００未満の低分子量成分を含む無機バインダを用いた塗料組成物から作製された塗膜は膜厚１０μｍ以上で剥離してしまい、膜厚５μｍと薄膜化した塗膜では光触媒活性が極端に低下した。これに対し、本発明に従って調整された塗料組成物から作製された塗膜では、膜厚が１５μｍと相当厚くなっても脱落することなく、優れた光触媒活性を呈した。
【００３２】
【発明の効果】
以上に説明したように、分子量分布が制御された無機バインダを光触媒分散トナーと混合して調整された塗料組成物を使用すると、オルガノアルコキシシランの加水分解時に生じる体積収縮に起因する収縮応力が分散された状態で塗膜が被塗物表面に形成されるため、厚塗り塗装した場合でも優れた耐剥離性を示す。しかも、アナターゼ型チタニア粉末，オルガノアルコキシシランを配合した光触媒分散トナーに少量の水を添加してオルガノアルコキシシランを部分加水分解し、アナターゼ型チタニア粉末表面のＯＨ基にアルコキシ基の加水分解生成物を反応させているので、アナターゼ型チタニア粉末の凝集沈殿が抑制され分散性が向上し、アナターゼ型チタニア粉末の光触媒活性が効率よく発現する光触媒塗膜となる。
【図面の簡単な説明】
【図１】低分子量成分を含む無機バインダを使用した場合の塗料組成物（ａ），塗膜（ｂ）における欠陥発生を説明する図
【図２】分子量分布を適正管理した無機バインダを用いた塗料組成物（ａ），塗膜（ｂ）で欠陥が抑制されることを説明する図
【符号の説明】
ｂ：基材 ｐ：光触媒塗膜 ｃ：クラック fc：微細クラック UV：紫外線又は雨水[0001]
[Industrial applications]
The present invention relates to a photocatalyst coating composition suitable for forming a coating film having excellent adhesion by maintaining a clean surface for a long time by a self-cleaning action by a photocatalytic reaction.
[0002]
[Prior art]
When the photocatalyst particles are dispersed in the coating film, a self-cleaning action is imparted to the coating film surface, and a clean coating film surface is maintained for a long period of time. An organic-based coating film is decomposed by active oxygen generated by light irradiation and causes a choking phenomenon. Therefore, a photocatalytic coating film is formed based on an inorganic substance that is not decomposed by active oxygen.
Examples of the coating composition for imparting photocatalytic activity to a coating film include a system in which an aqueous dispersion sol of TiO 2 is dispersed in a water / ethanol mixed solvent in which an alkoxide such as tetraalkoxysilane is dissolved (WO96 / 29375), and an organosilica sol. A system in which TiO 2 powder is dispersed in a solution dissolved in a solvent (JP-A-8-67835), a system in which silane-treated TiO 2 powder is dispersed in a silicone resin (JP-A-9-227831), and the like. It has been reported.
[0003]
Tetraalkoxysilane used as a binder for photocatalyst particles such as titanium oxide crosslinks and cures by hydrolysis and condensation reactions, so that the volume shrinkage during curing is large. The volume shrinkage becomes a very large shrinkage stress in the cured coating film and remains without being alleviated. Residual stress is a cause of peeling of a coating film when a thick coating having a dry film thickness of 5 μm or more is applied. Therefore, thin coating has to be avoided to avoid defects caused by residual stress.
[0004]
The thin coating is disadvantageous not only in that the photocatalytic activity required for the purifying action cannot be fully utilized, but also in the performance and quality stability of the photocatalytic coating film. For example, it is difficult to form a coating film having a uniform thickness on the surface of a large-area object to be coated, and it is inevitable that a partial film thickness reflecting slight irregularities and distortion on the surface is inevitable. Even when applying to an object having a complicated surface shape, a thick film portion that mimics the unevenness of the surface is likely to occur. In the thick film portion, the influence of shrinkage stress due to the volume shrinkage of the tetraalkoxysilane appears, and peeling of the coating film easily occurs.
In a coating composition in which TiO 2 powder is dispersed in a solution in which an organosilica sol is dissolved in an organic solvent, TiO 2 is insufficiently dispersed and easily agglomerated. Control is also difficult. With coating composition of TiO 2 powder silane treated to improve dispersibility of TiO 2 powder dispersed in a silicone resin is susceptible of thick film, the number of organic components contained in the coating film , Resulting in a coating film that is easily choked by decomposition by the photocatalytic particles.
[0005]
[Problems to be solved by the invention]
Therefore, the present inventors have introduced that the aggregation and precipitation of anatase-type titania powder can be prevented by adding a part of the organoalkoxysilane as a binder component to the photocatalyst-dispersed toner in advance (Japanese Patent Application Laid-Open No. 2002-105357). . The organoalkoxysilane covers the surface of the anatase-type titania powder, and the zeta potential of the powder surface deviates from the pH value of the inorganic binder. As a result, it is presumed that the aggregation and precipitation of the anatase-type titania powder are suppressed even when mixed with an inorganic binder.
When an inorganic binder containing very little organic component and containing colloidal silica as a main component is used, a coating film having excellent durability can be formed by suppressing chalking. A large amount of colloidal silica contained in the coating film contributes to stress relaxation, and a coating film having excellent crack resistance is formed even in a thick coating as compared with a binder of a silane condensate alone.
[0006]
[Means for Solving the Problems]
The present invention is a further improvement of the photocatalyst coating composition introduced in the prior application and JP-A-2002-105357, and by appropriately controlling the molecular weight distribution of the inorganic binder to be mixed in the photocatalyst coating composition, a thick coating. An object of the present invention is to form a photocatalytic coating film that does not easily peel off even when coated and exhibits excellent cleaning action.
[0007]
The photocatalyst coating composition proposed in the present invention contains a photocatalyst-dispersed toner and an inorganic binder.
The photocatalyst-dispersed toner is prepared by mixing TiO 2 powder, organoalkoxysilane, and water in a mixed solvent of isopropanol and ethylene glycol monobutyl ether. Anatase type titania powder having a particle size of 5 to 200 nm is used as the TiO 2 powder, and is blended at a ratio occupying 5 to 80% by mass of the solid content of the coating composition. The organoalkoxysilane has a general formula of R 1 Si (OR 2 ) 3 [R 1 is an alkyl group having 1 to 3 carbon atoms, a vinyl group, a 3,4-epoxycyclohexyl group, a γ-glycidoxypropyl group, a γ-mercapto group. A propyl group or a chloropropyl group, and R 2 is an alkyl group or an aryl group having 1 to 4 carbon atoms], and is preferably added at a ratio of 1 to 10% by mass. The amount of water to be added is selected within a range that partially hydrolyzes the organoalkoxysilane but does not allow the dehydration-condensation reaction between the organoalkoxysilanes to proceed, specifically, a range of 0.1 to 10% by mass.
[0008]
The inorganic binder has a solid content of 40 to 70% by mass of silica, 30 to 60% by mass of organohydroxysilane and a partial condensate of organohydroxysilane dispersed in a mixed solution of water / isopropanol / ethylene glycol monobutyl ether. The organohydroxysilane is represented by the general formula R 1 Si (OH) 3 [R 1 is an alkyl group having 1 to 3 carbon atoms, vinyl group, 3,4-epoxycyclohexyl group, γ-glycidoxypropyl group, γ-mercaptopropyl Or a chloropropyl group]. The molecular aggregate in which the organohydroxysilane and the partial condensate of the organohydroxysilane are bonded to silica is adjusted to a predetermined molecular weight distribution by adjusting the temperature and time during hydrolysis and condensation. As the silica, a colloidal silica, mainly an aqueous colloidal silica dispersion is used.
[0009]
[Action]
The organoalkoxysilane compounded in the photocatalyst-dispersed toner is adsorbed on the surface of the anatase-type titania powder as the organoalkoxysilane, or exists in a state of being simply dispersed in a solvent. Although the adsorbed organoalkoxysilane improves the dispersibility of the anatase-type titania powder, it cannot be said that the dispersibility is insufficient when stored for a long time.
In systems where water is present, the alkoxy groups of the organoalkoxysilane are partially hydrolyzed. The hydrolysis product binds to the OH group on the surface of the anatase titania powder, and the organoalkoxysilane adheres to the surface of the anatase titania powder via this bond. The anatase-type titania powder has improved dispersibility due to the adhesion of the organoalkoxysilane, and is suspended in the photocatalyst-dispersed toner for a long time without aggregation and precipitation. As a result, a photocatalyst-dispersed toner having excellent storage stability can be obtained. Good dispersibility is maintained even after mixing with the inorganic binder.
[0010]
The amount of organoalkoxysilane attached to the surface of the anatase titania powder can be controlled by the amount of water added to the photocatalyst-dispersed toner, and the improvement in dispersibility due to the organoalkoxysilane attachment can be seen at an amount of water of 0.1% by mass or more. As the amount of water added increases, the amount of organoalkoxysilane adhering to the surface of the anatase titania powder increases, and the dispersibility of the anatase titania powder improves. However, when an excess amount of water exceeding 10% by mass is added, the hydrolysis product of the alkoxy group attached to the surface of the anatase-type titania powder becomes too large, and the photocatalytic activity is impaired. The addition of an excessive amount of water promotes the dehydration-condensation of the organoalkoxysilanes added to the photocatalyst-dispersed toner, and the ratio of the hydrolysis products adhering to the surface of the anatase-type titania powder is rather reduced.
[0011]
It is preferable that components other than water mixed in the photocatalyst-dispersed toner be determined as follows.
As the photocatalyst, an anatase-type titania powder having a particle diameter of 5 to 200 nm, which has high photocatalytic activity and excellent chemical stability, is blended at a ratio of 5 to 80% by mass. Powder having a particle size of 5 nm is difficult to produce itself, and a particle size exceeding 200 nm results in insufficient photocatalytic activity. If the blending ratio of the anatase type titania powder is less than 5% by mass, there is no thixotropy and the particles settle quickly and the cake becomes solid. Therefore, it is difficult to redisperse the toner when it is used. Conversely, if the amount is more than 80% by mass, the thixotropy becomes too high, and the fluidity of the toner is impaired.
[0012]
The organoalkoxysilane has a general formula R 1 Si (OR 2 ) 3 [R 1 is an alkyl group, vinyl group, 3,4-epoxycyclohexyl group, γ-glycidoxypropyl group, γ-mercaptopropyl group or chloropropyl group. , R 2 is an alkyl or aryl group having 1 to 4 carbon atoms], and is blended at a ratio of 1 to 10% by mass. The reaction of the organoalkoxysilane with each other is suppressed by the introduction of the organic functional group, and the ratio of the organoalkoxysilane attached to the surface of the anatase titania powder increases. In this regard, in the case of tetraalkoxysilane, hydrolysis proceeds excessively and not only adheres to the surface of the anatase-type titania powder, but also increases the ratio of not contributing to the dispersion of the anatase-type titania powder as a result of mutual reaction of silanes.
[0013]
Even with organoalkoxysilanes, if the number of organic functional groups is two or more, the amount of organic substances attached to the surface of the anatase-type titania powder increases. When a photocatalytic coating film prepared from a dispersion toner of anatase-type titania powder to which an organic substance is excessively adhered is placed in a light irradiation environment, the organic substance is decomposed and chalking of the coating film proceeds in a short time. Therefore, only one organic functional group directly bonded to Si is used, and 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 Preferably, it is a chloropropyl group.
[0014]
The blending amount of the organoalkoxysilane is determined in the range of 1 to 10% by mass. When the amount is less than 1% by mass, the dispersibility is not improved. On the other hand, when the amount exceeds 10% by mass, the coverage of the surface of the anatase-type titania powder becomes too high, and the photocatalytic activity after forming the coating film is extremely high. descend. The amount of the organoalkoxysilane depends on the particle size of the anatase type titania powder. For example, 7 nm TiO 2 powder has a large surface area of about 300 m 2 / g, so that 8% by mass of organoalkoxysilane gives the greatest effect. The surface area of TiO 2 powder having a particle size of 20 nm is about 50 m 2 / g, and it is most effective when the content of the organoalkoxysilane is 3% by mass.
[0015]
As the solvent, a mixed solvent of isopropanol and ethylene glycol monobutyl ether is used. The mixing ratio is preferably isopropanol: 40 to 60% by mass and ethylene glycol monobutyl ether: 40 to 60% by mass. By adjusting the mixing ratio, the dispersibility of the anatase-type titania powder is improved, and the volatilization speed is appropriately controlled when forming a coating film after mixing the photocatalyst-dispersed toner with a binder, so that cracks leading to peeling can be obtained. Is prevented from occurring.
The photocatalyst-dispersed toner is prepared by adding an anatase-type titania powder to a mixed solvent of isopropanol / ethylene glycol monobutyl ether to which organoalkoxysilane and water are added, stirring the mixture with a stirrer, and then using a horizontal mill in which the filled beads are maintained in a stirring state. It is prepared by injecting at a flow rate of 1 liter / min. If necessary, colorants such as pigments and dyes, and additives such as thickeners are added.
[0016]
The inorganic binder is prepared by dispersing silica, organohydroxysilane and a partial condensate of organohydroxysilane as a solid content in a mixed solution of water / isopropanol / ethylene glycol monobutyl ether. The colloidal silica is preferably a mixture of an aqueous colloidal silica dispersion and an isopropanol-based colloidal silica dispersion. The average particle size of the silica is preferably 150 nm or less (more preferably, 30 nm) or less, and acidic colloidal silica is preferably used to secure the storage stability of the inorganic binder.
Organohydroxysilanes and partial condensates of organohydroxysilanes are obtained by hydrolysis of organoalkoxysilanes and are represented by the general formula R 1 Si (OH) 3 . As a representative organoalkoxysilane, the same compound R 1 Si (OR 2 ) 3 as one component of the photocatalyst-dispersed toner can be used. As the partial condensate of organohydroxysilane, an oligomer obtained by partially condensing an organohydroxysilane of the general formula R 1 Si (OH) 3 can be used.
[0017]
The solid content of the inorganic binder is a molecular assembly in which colloidal silica is used as a core and organohydroxysilane and a partial condensate of organohydroxysilane are bonded by dehydration condensation. When an inorganic binder is mixed with a photocatalyst-dispersed toner, a molecular network reacts and bonds with anatase-type titania powder to which a partial condensate of organohydroxysilane is attached and colloidal silica as a nucleus. The titania powder is uniformly dispersed in the coating film.
A molecular assembly in which an organohydroxysilane and a partial condensate of an organohydroxysilane are bound to colloidal silica is controlled to a predetermined molecular weight and a predetermined molecular weight distribution by controlling a reaction time and a reaction temperature during polymerization. The molecular weight distribution is adjusted to have a molecular weight of 300 or more, a molecular weight of 300 to 500 is 0 to 20%, a molecular weight of 500 to 1000 is 20 to 40%, and a molecular weight of 1000 to 10000 is 40 to 70%. The peel resistance is improved.
[0018]
The influence of the molecular weight distribution on the peel resistance is considered as follows, and is also supported by the examples described later. In a coating film made from a coating composition containing a low-molecular-weight component, the OH group of the low-molecular-weight component acts as a reaction point, applying a large stress to the coating film, and there is a single molecule that has not been completely hydrolyzed. However, no binding to colloidal silica occurred (FIG. 1a). Therefore, there are many reaction points during the formation of the coating film, and the dehydration condensation reaction proceeds rapidly, and as a result, a large stress remains in the coating film. In addition, the low molecular weight component (unreacted component) easily bleeds into the surface layer of the coating film p, and a curing reaction occurs in an environment exposed to rainwater or ultraviolet irradiation UV. As a result of the curing reaction, shrinkage stress due to volume shrinkage is generated in the coating film p, and a crack c reaching the base material b is generated (FIG. 1b).
[0019]
On the other hand, in a coating film prepared from a coating composition containing a component in which hydrolysis of the alkoxide has been completely completed, the bond between the alkoxide and the colloidal silica has sufficiently proceeded, and a large molecule surrounds the colloidal silica. Therefore, the number of reaction points is small, and the reaction gradually proceeds during the formation of the coating film, so that the residual stress is also small (FIG. 2A). In addition, there is no bleeding of unreacted components on the surface of the coating film, and fine cracks fc are present inside the coating film. Therefore, the curing reaction does not proceed in an environment exposed to rainwater or ultraviolet irradiation, and even if there is a stress applied to the coating film, it is dispersed by fine cracks, and does not grow to cracks reaching the base material (see FIG. 2b).
[0020]
The binding state by the hydrolysis and dehydration condensation reactions can be measured by gel filtration chromatography and evaluated by the molecular weight calculated from a calibration curve prepared using polystyrene as a standard substance. Specifically, after diluting 20-fold with an inorganic binder and tetrahydrofuran and filtering through a 1 μm filter, gel filtration chromatography (HLC 8020: manufactured by Tosoh Corporation) using 1000/2000 Shoudex 801, 802 was used for the column. Using tetrahydrofuran as a measurement solvent, the molecular weight distribution was determined by an RI detector. When the condensation proceeds to a molecular weight of 300 or more and low molecular weight components less than 300 disappear, the influence of excess OH groups and low molecular weight components bleeding on the coating film surface is suppressed. Above all, when the molecular weight distribution is controlled to be 0 to 20% for the molecular weight of 300 to 500, 20 to 40% for the molecular weight of 500 to 1000, and 40 to 70% for the molecular weight of 1,000 to 10,000, the effect of suppressing the influence of the low molecular weight component is effective. Become
[0021]
The solvent is composed of water in the colloidal silica dispersion, water condensed with organohydroxysilane, alcohol generated by hydrolysis of organohydroxysilane, isopropanol, and ethylene glycol monobutyl ether. When at least 20% by mass of ethylene glycol monobutyl ether is blended as a solvent for the inorganic binder, the storage stability of the inorganic binder is remarkably improved, and a coating composition excellent in coating workability and film forming property is obtained. In a conventional inorganic binder, storage stability is deteriorated when water content of 20% by mass or more is contained. However, in a system containing 20% by mass or more of ethylene glycol monobutyl ether, even if water content of 20% by mass or more is contained, it is not sufficient. Storage stability is maintained. The inorganic binder is preferably adjusted to a pH of 4 to 5 using an organic amine such as aqueous ammonia, triethanolamine, or dimethylethanolamine in order to improve the storage stability.
[0022]
The photocatalyst-dispersed toner is prepared by adding an anatase-type titania powder to a mixed solvent of isopropanol / ethylene glycol monobutyl ether to which organoalkoxysilane and water are added, stirring the mixture with a stirrer, and then using a horizontal mill in which the filled beads are maintained in a stirring state. It is prepared by injecting at a flow rate of 1 liter / min. If necessary, an additive such as a coloring agent such as a pigment or a dye, or a thickener may be added.
The inorganic binder is obtained by hydrolyzing the organoalkoxysilane added to the colloidal silica dispersion to form a partial condensate of the organohydroxysilane and the organohydroxysilane, and then diluting with a solvent, after diluting the colloidal silica dispersion with the solvent. , An organoalkoxysilane and hydrolysis. When the organoalkoxysilane is added to colloidal silica for hydrolysis, the reaction is carried out while maintaining the liquid temperature at 10 to 80 ° C. and stirring under normal pressure for 1 to 24 hours. A part of the non-aqueous colloidal silica dispersion may be added later, and further heated and reacted. Upon hydrolysis of the organoalkoxysilane, a small amount of a hydrolysis catalyst such as an inorganic acid or an organic acid may be added.
[0023]
The photocatalyst coating composition is prepared by further stirring while gradually adding the inorganic binder to the sufficiently stirred photocatalyst-dispersed toner. At this time, the photocatalyst-dispersed toner and the inorganic binder are mixed at a mixing ratio of 5 to 80% by mass of TiO 2 as a solid content. To obtain a sufficient photocatalytic activity, a TiO 2 content of 5% by mass or more is necessary. However, if an excessive amount of TiO 2 exceeds 80% by mass, the adhesion of the coating film is reduced.
The prepared paint is applied to the pretreated base material by a spray method, a dipping method, a flow coating method, a roll coating method, a screen printing method, an electrostatic coating method, or the like. After coating, by heating at 80 to 130 ° C. for 1 to 30 minutes, a coating film having excellent adhesion to the substrate is formed. The thickness of the coating film cannot be determined unconditionally because it varies depending on the type and use of the substrate, but is usually adjusted in the range of 1 to 30 μm. Substrates to which the photocatalytic coating composition is applied include metals such as ordinary steel, plated steel plates, stainless steel plates, aluminum, copper, and brass, cement, concrete, tiles, slate plates, glass, and stone materials. Depending on the temperature at the time of heating, it can be applied to an organic material such as plastic.
[0024]
【Example】
Preparation of an anatase-type titania powder-dispersed toner To a mixed solvent of isopropanol: 50% by mass and ethylene glycol monobutyl ether: 50% by mass, 3% by mass of organoalkoxysilane and 0.3% by mass of water were added, and a particle size of 20 nm was further added. Anatase titania powder was added. The addition amount of the anatase type titania powder was set at a ratio of 40% by mass of the whole paint. A photocatalyst-dispersed toner was prepared by dispersing the mixture with a stirrer using a bead mill.
[0025]
Preparation of inorganic binder Aqueous colloidal silica: 21.2 g (average particle size 5 to 20 nm, solid content 20 mass%, pH 3.0) and isopropanol colloidal silica 62.6 g (average particle size 5 to 20 nm, solid content 20 mass) %), 13.9 g of methyltrimethoxysilane was added, and the mixture was stirred at 80 ° C. for 12 hours to complete the hydrolysis. Next, a mixed solvent of isopropanol: 33% by mass and ethylene glycol monobutyl ether: 67% by mass was added to the hydrolyzate, and the pH was adjusted to 4.5 by further adding aqueous ammonia.
The obtained photocatalyst-dispersed toner and inorganic binder were mixed and stirred at such a ratio that the TiO 2 content in the solid content was 40% by mass, and filtered using a 50 μm mesh to form a coating.
[0026]
A paint was spray-coated on the pretreated SUS304 stainless steel base material and heated at 200 ° C. for 20 minutes to form a coating film having a thickness of 10 μm. For comparison, a coating prepared by mixing a water-free photocatalyst-dispersed toner with an inorganic binder (Comparative Example 1) and a coating prepared by mixing an inorganic binder with a molecular weight of less than 300 by adjusting the reaction time with a photocatalyst-dispersed toner A SUS304 stainless steel substrate was similarly coated using (Comparative Example 2).
[0027]
The dispersibility of the prepared photocatalytic coating composition, the peeling resistance of the coating film, and the photocatalytic activity were evaluated by the following methods.
(1) Dispersibility of Photocatalytic Coating Composition After forming a coating by mixing a photocatalyst-dispersed toner and an inorganic binder, the aggregation state of TiO 2 particles was examined one day later. The coating composition in which no ridges of 5 μm or more are detected is represented by ○, the coating composition in which no ridges of 10 μm or more are detected but 5 to 10 μm is detected is Δ, and the coating composition in which a ridge of 10 μm or more is formed is indicated by ×. Was evaluated.
[0028]
(2) Peeling resistance of the coating film The peeling resistance of the coating film was examined by a sunshine weather test at 63 ° C. Was evaluated as x, and the peel resistance was evaluated.
(3) The weight of salad oil remaining on the test piece after adhering salad oil to the surface of the test piece at a photocatalytic activity of 0.2 mg / cm 2 and irradiating it with black light of 5 mW / cm 2 for 24 hours. Was measured, and the photocatalytic activity was evaluated using the weight loss rate as an oil decomposition rate.
[0029]
As can be seen from the investigation results in Table 1, the coating composition obtained from the photocatalyst-dispersed toner to which the organoalkoxysilane and water were added exhibited good dispersibility regardless of the molecular weight distribution of the inorganic binder. On the other hand, in the coating composition using the water-free photocatalyst-dispersed toner (Comparative Example 11), bumps of 5 to 10 μm were detected.
[0030]
Each of the coating compositions shown in Table 1 was spray-coated on a pretreated SUS304 stainless steel substrate to form a coating film whose film thickness was adjusted according to the coating amount. Table 2 shows the results of examining the peel resistance and photocatalytic activity of the obtained coating film.
As is clear from Table 2, the coating film produced from the coating composition using the inorganic binder containing a low molecular weight component having a molecular weight of less than 300 was peeled at a film thickness of 10 μm or more, and the coating film having a thickness of 5 μm was reduced. In the film, the photocatalytic activity was extremely reduced. On the other hand, the coating film prepared from the coating composition prepared according to the present invention exhibited excellent photocatalytic activity without falling off even when the film thickness was considerably increased to 15 μm.
[0032]
【The invention's effect】
As described above, when a coating composition prepared by mixing an inorganic binder having a controlled molecular weight distribution with a photocatalyst-dispersed toner is used, shrinkage stress caused by volume shrinkage generated during hydrolysis of organoalkoxysilane is dispersed. Since the coating film is formed on the surface of the object to be coated in the coated state, it exhibits excellent peeling resistance even in the case of thick coating. In addition, a small amount of water is added to the photocatalyst-dispersed toner containing the anatase titania powder and the organoalkoxysilane to partially hydrolyze the organoalkoxysilane, and the hydrolysis product of the alkoxy group is converted to the OH group on the surface of the anatase titania powder. Because of the reaction, the coagulation and precipitation of the anatase-type titania powder is suppressed, the dispersibility is improved, and a photocatalytic coating film that efficiently exhibits the photocatalytic activity of the anatase-type titania powder is obtained.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating the occurrence of defects in a coating composition (a) and a coating film (b) when an inorganic binder containing a low molecular weight component is used. FIG. 2 Using an inorganic binder whose molecular weight distribution is appropriately controlled. Diagram explaining that defects are suppressed in coating composition (a) and coating film (b).
b: substrate p: photocatalytic coating c: crack fc: fine crack UV: ultraviolet light or rainwater
Claims (4)
光触媒分散トナーは、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アナターゼ型チタニア粉末，オルガノアルコキシシラン，水を配合しており、
無機バインダは、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％及びシリカ４０〜７０質量％の固形分を水／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液に分散させており、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結合した分子集合体がスチレン換算で分子量が３００以上で、分子量３００〜５００が０〜２０％，分子量５００〜１０００が２０〜４０％，分子量１０００〜１００００が４０〜７０％の分子量分布に管理されていることを特徴とする光触媒塗料組成物。A coating composition comprising a photocatalyst-dispersed toner and an inorganic binder,
The photocatalyst-dispersed toner contains an anatase-type titania powder, an organoalkoxysilane, and water in a mixed solvent of isopropanol and ethylene glycol monobutyl ether.
The inorganic binder has a solid content of 30 to 60% by mass of organohydroxysilane and a partial condensate of organohydroxysilane and 40 to 70% by mass of silica dispersed in a mixed solution of water / isopropanol / ethylene glycol monobutyl ether. Is a nucleus, and a molecular assembly in which an organohydroxysilane and a partial condensate of the organohydroxysilane are bonded has a molecular weight of 300 or more in terms of styrene, 0 to 20% for a 300 to 500 molecular weight, 20 to 40% for a 500 to 1000 molecular weight, A photocatalyst coating composition, wherein the molecular weight is controlled to a molecular weight distribution of from 40 to 70%.
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