JP3578059B2 - Solar heat reflective painted metal plate - Google Patents

Description

Ｒ_{Ｅ／ＮＩＲ} ： ０．８〜２．１ μｍの波長領域での太陽熱反射率（％） 、
Ｅλ ：太陽熱の分光強度、
Ｒλ ：分光反射率 （分光光度計により測定） 。
【００３２】
塗膜の太陽熱透過率とは、塗膜の分光透過率 （Ｔλ） より算出される当該波長領域でのスペクトルの強さを考慮した太陽熱透過率である。 ０．８〜２．１ μｍの波長領域での塗膜の太陽熱透過率 （Ｔ_{Ｅ／ＮＩＲ} ） は次の（２） 式により求められる。
【００３３】
【数２】

Ｔ_{Ｅ／ＮＩＲ} ： ０．８〜２．１ μｍの波長領域での塗膜の太陽熱透過率（％） 、
Ｅλ ：太陽熱の分光強度、
Ｒλ ：分光透過率 （分光光度計により測定） 。
【００３４】
本発明において裏面の放射率とは、 ４．５〜２５μｍの波長領域において裏面の分光反射率 （Ｒλ） より算出される、プランクの熱放射スペクトル分布における絶対温度 ２９３Ｋとした場合の相対値を考慮した放射率である。放射率αは次の（３） 式により求められる。
【００３５】
【数３】

α ：放射率 （％） 、
Ｇλ：プランクの熱放射スペクトル分布において絶対温度 ２９３Ｋとした場合の相対値、
Ｒλ：分光反射率 （分光光度計により測定） 。
【００３６】
【発明の実施の形態】
本発明の塗装金属板は、金属基板の日射を受ける少なくとも片面に塗装を施したものであり、日射を受ける面 （以下、日射面とも記す） の ０．８〜２．１ μｍの波長領域 （＝近赤外線領域） での太陽熱反射率 （Ｒ_{Ｅ／ＮＩＲ} ） が２０％以上である。日射面のＲ_{Ｅ／ＮＩＲ} が２０％に満たないと、太陽熱反射性塗装金属板としての基板の昇温抑制効果が低下する。日射面のＲ_{Ｅ／ＮＩＲ} は、好ましくは３０％以上である。
【００３７】
この塗装金属板は、１態様では、近赤外線領域での太陽熱反射率 （Ｒ_{Ｅ／ＮＩＲ} ） が１０％以上である顔料 （即ち、反射性顔料） を２〜７０質量％含有する少なくとも１層の反射性塗膜をその日射面に備えたものでよい。塗装金属板が日射面に複数の塗膜を備えている場合には、少なくとも外層塗膜を反射性塗膜とすることが好ましい。即ち、外層塗膜だけを反射性塗膜としてもよく、或いは、さらに内層塗膜の一部または全部も反射性塗膜とすることができる。外層塗膜が薄く、反射性顔料を含有させてもその隠蔽性が十分ではないといった場合には、内層塗膜にも反射性顔料を含有させてもよい。
【００３８】
本発明における外層塗膜とは、塗装金属板の色彩を決定する塗装工程で施される塗膜を意味する。耐汚染性などの性能向上を目的として、外層塗膜の上にさらにクリヤー皮膜を施す場合もあるが、本発明ではクリヤー皮膜は外層塗膜とは考えない。
【００３９】
別の態様では、日射面の塗膜が、 ０．８〜２．１ μｍの波長領域での太陽熱透過率 （Ｔ_{Ｅ／ＮＩＲ} ） が２０％以上である、太陽熱透過率が高い顔料含有塗膜であり、金属基板の少なくとも日射を受ける面の ０．８〜２．１ μｍの波長領域での太陽熱反射率 （Ｒ_{Ｅ／ＮＩＲ} ） が４０％以上と高い。この場合には、基板から反射した太陽熱が塗膜を通って外部に反射されることで、塗装金属板が高い太陽熱反射性を示すことができる。
【００４０】
塗装金属板の日射面の反射率、塗膜に使用する反射性顔料の反射率、および塗膜の太陽熱透過率のいずれについても、本発明では、近赤外線領域である ０．８〜２．１ μｍの波長領域の波長に対する太陽熱反射率 （Ｒ_{Ｅ／ＮＩＲ} ） または太陽熱透過率 （Ｔ_{Ｅ／ＮＩＲ} ） により規定したのは、可視光線領域の波長に対する太陽熱反射率や太陽熱透過率は色彩に依存して決まるためである。可視光線領域の波長に対しても太陽熱反射率や太陽熱透過率を規定すると、塗装金属板の色彩の自由度がなくなり、建築用外装材として不適格となる。本発明によれば、近赤外線領域の波長に対して太陽熱反射率や太陽熱透過率を規定するだけで、日射を受けた場合の基板温度上昇を著しく抑制することができる。
塗膜：
（１） 反射性塗膜
塗装金属板の日射面に設ける反射性塗膜は、上記のように近赤外線領域での太陽熱反射率が１０％以上である反射性顔料を２〜７０質量％含有する （該塗膜の乾燥重量に基づいて、以下同じ） 。反射性顔料の含有量 （複数の反射性顔料を併用した場合にはそれらの合計量） が、その塗膜中で２質量％に満たないと、金属板に十分な太陽熱反射性を付与することができず、また着色力も不足して所望の色彩を得るのに厚膜塗装が必要になる。この含有量は好ましくは５質量％以上である。反射性顔料の含有量がその塗膜中で７０質量％を超えると、塗膜の加工性が損なわれる。含有量の上限は好ましくは６０質量％である。
【００４１】
反射性塗膜に含有させる反射性顔料は１種類に限る必要はなく、色相、耐候性、色安定性を考慮し、上記の条件を満足する１種もしくは２種以上の顔料を任意に選択できる。２種以上の反射性顔料を使用する場合には、これらの合計含有量が上記の範囲にあればよい。
【００４２】
本発明の塗装金属板に用いる反射性顔料は、安全で、耐水性、耐候性に優れ、長期間遮熱効果を維持するものが望ましい。中でも、金属の酸化物、硫化物、クロム酸塩などの金属化合物や、不溶性色素 （色素顔料） 、レーキ顔料などから選んだ顔料を用いるのが好ましい。
【００４３】
顔料の平均粒径が５０μｍを超えると、太陽熱反射性が劣るため、反射性顔料の平均粒径は５０μｍ以下とするのが好ましい。耐汚染性、耐候性、色安定性の観点から、反射性顔料の平均粒径はより好ましくは２０μｍ以下、さらに好ましくは１０μｍ以下である。
【００４４】
反射性塗膜には、上記の反射性顔料の他に、所望の色彩や隠蔽性、耐食性等の塗膜性能を得るのに必要な着色顔料、防錆顔料、ならびに基板表面とバインダーである有機樹脂 （例えば、ポリエステル樹脂、フッ素系樹脂など） との密着性や塗膜自体の凝集強度を高めたり、下地の隠蔽性や明度を向上させる目的で、例えばシリカ、アルミナ、炭酸カルシウム、硫酸バリウム、カオリン、クレー、タルク、ネフェリン、サイナイト、雲母、気泡含有顔料等といった体質顔料を含有させても構わない。
【００４５】
顔料を保持するバインダーとしては、太陽光に曝されても黄変、変色、光沢低下、白亜化を起こしにくく、長年使用しても美観の維持に優れると共に、太陽光の隠蔽効果を長期間維持できる有機樹脂を使用するのが好ましい。
【００４６】
このような樹脂としては、アクリル樹脂、ポリエステル樹脂、ポリオレフィン樹脂、フッ素系樹脂等を始めとする各種有機樹脂が挙げられ、それらのいずれか１種を用いればよいが、２種以上を混合して用いても構わない。これらの有機樹脂の含有量は、固形分として塗膜の１０〜９０質量％の範囲とするのが好ましい。
【００４７】
樹脂中には、合成微粉シリカ、有機ベントナイト、カルボキシメチルセルロース、ポリビニルアルコール等の増粘剤、メラミン系、ベンゾグアナミン系、イソシアネート系等の架橋剤、ポリアクリル酸、ポリアクリル酸塩等の分散剤、防汚用の光触媒等を含有させても構わない。
【００４８】
反射性塗膜の厚さは３〜２００ μｍの範囲が好ましい。３μｍより薄い塗膜は色相が安定しないことがある。この塗膜の厚さはより好ましくは７μｍ以上である。塗膜の厚さが２００ μｍを超えると、加工時に塗膜の剥離や割れが生じることがあるうえ、複数回の塗装作業を必要とするようになり、経済性も劣る。より好ましくは５０μｍ以下である。
【００４９】
内層塗膜としての下塗り塗膜あるいは中塗り塗膜には、通常、太陽熱を吸収し易い顔料が含有されている。従って、これらの内層塗膜の反射性顔料の含有量が２％に満たない場合は、太陽熱反射性を阻害しないように、その厚さは薄い方が好ましく、２００ μｍ以下とするのがよい。より好ましくは５０μｍ以下である。
【００５０】
本発明の塗装金属板の外層塗膜は、使用する塗料にアルミフレーク （鱗片状アルミニウム顔料） を配合してメタリック塗膜としたり、艶消し剤を配合して艶消し塗膜としたり、任意の意匠性を付与することができる。また、反射性塗膜は本発明の塗装金属板の外層塗膜、即ち、最上層として設けるのが好ましいが、例えばアルミフレークを配合したメタリック塗装とする場合などは、必要に応じて反射性塗膜の上に顔料を含まないクリアー層、または顔料を僅かに含む半透明な層を設けても構わない。
（２） 太陽熱透過率 （Ｔ_{Ｅ／ＮＩＲ} ） が２０％以上の塗膜
この場合の塗膜も、２０％以上のＴ_{Ｅ／ＮＩＲ} を確保するため、０．８ 〜２．１ μｍの近赤外線領域での太陽熱吸収率が高くならないように塗膜を構成する点を除けば、基本的には上記の太陽熱反射性塗膜と同様でよい。
【００５１】
顔料としては、反射性顔料について列挙したような種類の顔料があるが、その中で近赤外線領域での光の吸収率が低く、透過率が高い顔料を使用すればよい。顔料の平均粒径や塗膜厚みが大き過ぎると、塗膜の太陽熱透過率が低下するので、顔料の平均粒径は２０μｍ以下の範囲が好ましく、塗膜厚みは１〜１００ μｍの範囲とすることが好ましい。バインダーとして用いる有機樹脂や塗膜に存在させる添加物は、塗膜の近赤外線領域での太陽熱透過率を阻害しないように選択することが好ましい。
【００５２】
前述したように、反射性顔料を２〜７０質量％含有する反射性塗膜であっても、顔料の種類や粒径、塗膜厚みその他の条件を適当に選択すると、Ｔ_{Ｅ／ＮＩＲ} が２０％以上の太陽熱透過性の塗膜とすることができる。
（３） 耐汚染性塗膜
前述したように、本発明の塗装金属板の日射面に汚染物質が付着して汚れると、太陽熱反射性が低下し、目的とする遮熱性能も低下する。従って、長期の性能保持のために、日射面の表面に耐汚染性を付与することが有利である。
【００５３】
屋外で使用する塗装金属板に付着する汚染物質は、ほとんどが疎水性の物質である。従って、日射面の汚染を抑制するには、疎水性の汚染物質が付着しにくいように、日射面の表面の水濡れ性を良くするのがよい。表面の水濡れ性を良くすれば、疎水性の汚染物質は表面に強く付着できず、降雨時に容易に洗い流されるので、汚染物質が蓄積することがない。このような水濡れ性を確保するには、日射面の表面の水に対する接触角が６０°以下となるようにすればよい。水に対する接触角が６０°以下という親水性の塗膜は、バインダーの一部または全部として、水酸基やカルボニル基等の極性基を有する親水性の有機樹脂を使用することにより得ることができる。接触角を調整するには、樹脂の極性基の種類や量を変化させるか、２種以上の樹脂を併用すればよい。
【００５４】
逆に、降雨時の雨滴に含有されることがある汚染物質が日射面に付着するのを妨げるため、日射面の表面を疎水性にして、雨滴が日射面に付着しにくくするのも、日射面の汚染を防ぐのに有効な方法である。このためには、日射面の表面の水に対する接触角を９０°以上にすることが好ましい。水に対する接触角が９０°以上という疎水性の塗膜は、バインダーとしてポリオレフィン樹脂やフッ素樹脂といった非極性の有機樹脂を使用することにより得られる。
【００５５】
本発明の塗装金属板に上記手段で耐汚染性を付与する場合、表面に現れる外層の太陽熱反射性塗膜のバインダー樹脂を親水性または疎水性の樹脂にして、この塗膜の水に対する接触角が６０°以下または９０°以上になるようにしてもよい。即ち、外層の太陽熱反射性塗膜それ自体に耐汚染性を付与するのである。ただし、この手法では、太陽熱反射性塗膜に使用するバインダー樹脂種が制限され、コスト高になったり、加工性、耐食性などの他の性能が所望レベルに達しないことがある。
【００５６】
別の態様として、太陽熱反射性塗膜の上に、水に対する接触角が６０°以下または９０°以上の表面を有する耐汚染性塗膜を別に形成することができる。この耐汚染性塗膜は、前述したように親水性または疎水性のバインダー樹脂を使用して形成することができる。その場合、耐汚染性塗膜の厚みは ０．５〜５０μｍとするのがよい。厚みが０．５ μｍに満たないと耐汚染性改善効果が小さく、５０μｍを超えると太陽熱反射性が阻害されることがある。この耐汚染性塗膜は、顔料を含有しないクリアー塗膜でよいが、太陽熱反射性あるいは太陽熱透過性を阻害しない限り、顔料を含有させることもできる。
（４） 裏面側の塗膜
本発明の塗装金属板は、基板の日射面となる側の片面だけに上述した反射性塗膜または太陽熱透過性の塗膜を有していればよい。室内の方を向く、基板の日射面と反対側の面（裏面）については特に制限されない。この裏面は必ずしも塗装面とする必要はないが、好ましくは放射率が７０％以下の面とする。
【００５７】
塗装金属板を建築用外装材として用いた場合、吸収された太陽熱は、室内空気の対流による伝導と、裏面からの放射により室内に伝達され、室内空気温度を上昇させる。従って、裏面からの室内への放射を抑制すれば、室内空気温度の上昇を抑制することが可能である。つまり、裏面の放射率を小さくすればよい。
【００５８】
放射率は、分光反射率の測定と前述の式（３） により求めることができる。裏面の放射率が７０％を越えると、室温の上昇が著しくなるので、この放射率を７０％以下、特に５０％以下とすることが有利である。
【００５９】
裏面の放射率を小さくするには、裏面の金属面にクリアー塗装を施すか、裏面の外層塗膜として、上述した反射性顔料の１種類以上を合計で２〜７０質量％含有する塗装（即ち、日射面側と同じ塗装でよい）、またはアルミニウムペイントの塗装を施すことが有効である。
【００６０】
アルミニウムペイントとは、鱗片状アルミニウム顔料を含有する塗料のことであり、鱗片状アルミニウム顔料を２〜３０質量％含有させた塗膜が適当である。鱗片状アルミニウム顔料は、同じ含有量で比べた場合に、他の顔料より放射性を小さくすることができる。この放射率の小さい塗膜の厚みは１〜２０μｍの範囲とすることが好ましい。その場合、塗膜中の鱗片状アルミニウム顔料の含有量は０．０５〜１．５ ｇ／ｍ^２の範囲内であることが好ましい。この含有量が０．０５ ｇ／ｍ^２ より少ないと、十分に小さい放射率を得ることができず、１．５ ｇ／ｍ^２を越えると加工時に塗膜の剥離や割れが生じることがある。
【００６１】
この放射率の小さい裏面側の塗膜にも、反射性塗膜について説明したのと同様に、上記の顔料以外に、着色顔料、防錆顔料や体質顔料を含有させても構わない。また、顔料を保持するバインダーとしては、反射性塗膜と同様の有機樹脂を使用するのが好ましい。さらに、反射性塗膜と同様に分散剤等の添加物を含有させてもよい。
基板：
金属基板としては、用途に必要な特性を備えた任意の金属板を使用することができ、その種類や化学組成は特に制限されない。例えば、低炭素鋼、高炭素鋼、高張力鋼板などに使用される低合金鋼からなる鋼板、あるいはこれらの鋼板を母材とするめっき鋼板、さらにはステンレス鋼板やアルミニウム板などが例示される。
【００６２】
基板の日射面に形成する塗膜が反射性塗膜である場合には、基板の種類によらず、太陽熱反射性が高い塗装金属板を得ることができる。従って、耐食性、強度等の塗装金属板に求められる特性を考慮して基板を選択すればよい。この場合に好ましい基板は、めっき鋼板、特に耐食性に優れたＺｎ系めっき鋼板 （純ＺｎめっきまたはＺｎ系合金めっき鋼板） およびＡｌ系めっき鋼板である。但し、後述するように反射性塗膜のＴ_{Ｅ／ＮＩＲ} が２０％以上と高い場合には、基板として太陽熱反射率の高いものを選ぶと、さらに高い太陽熱反射性を有する塗装金属板とすることができる。
【００６３】
基板の日射面に反射性顔料を含有する塗膜を形成しても、この塗膜の膜厚や、顔料の含有量によっては、近赤外線領域での塗膜の隠蔽力が不足し、太陽熱反射性塗装金属板としての太陽熱反射性が十分ではないことがある。これは、近赤外線は可視光線に比べ塗膜の透過率が高いことに起因する。このような場合には、基板として近赤外域の太陽熱反射性の良いものを使用し、基板からの太陽熱反射性を利用して塗装金属板の反射性を高めるのが有効である。このように、太陽熱反射性の高い金属基板を用いて、基板からの反射を利用して太陽熱反射性の高い塗装金属板を得る場合には、塗膜を太陽熱透過率Ｔ_{Ｅ／ＮＩＲ} が２０％以上の塗膜とする。この塗膜が太陽熱反射性であると、塗装金属板の太陽熱反射性はさらに高まる。
【００６４】
具体的には、日射面に形成した塗膜の ０．８〜２．１ μｍの波長領域での太陽熱透過率 （Ｔ_{Ｅ／ＮＩＲ} ） が２０％以上である場合には、太陽熱反射性は基板の反射性の影響を大きく受けるようになる。その場合、 ０．８〜２．１ μｍの波長領域での太陽熱反射率 （Ｒ_{Ｅ／ＮＩＲ} ） が４０％以上である基板を用いると、日射面の太陽熱反射性の高い塗装金属板となる。Ｒ_{Ｅ／ＮＩＲ} が４０％に満たない場合には、日射面側の塗装面の反射性が低下する。好ましくは、基板のＲ_{Ｅ／ＮＩＲ} は５０％以上、さらに好ましくは６０％以上である。
【００６５】
基板がめっき鋼板である場合、めっき種は特に限定するものではないが、太陽光に対する反射性がよく、基板のＲ_{Ｅ／ＮＩＲ} が４０％以上になることと、めっき作業の経済性から、Ａｌ−Ｚｎ系、Ａｌ−Ｍｎ系、Ａｌ−Ｓｉ系等が好適である。中でも、アルミニウムを５０質量％以上含有するめっき皮膜を備えたものが好適であり、純アルミニウムめっきでもよい。めっき皮膜には、さらに、適量のＮｉ、Ｃｒ、Ｆｅ、Ｃｏ等の合金元素を含有させても構わない。このようなめっき皮膜は、太陽熱反射性が高いうえに、基板の防食性や経済性にも優れるという特長を有する。なお、Ｚｎ系めっき鋼板でも、Ｒ_{Ｅ／ＮＩＲ} が４０％以上となる場合がある。
【００６６】
めっき皮膜の付着量は任意であるが、０．０１μｍ以上の厚さのめっき皮膜が、太陽熱反射性が良好になるので好ましい。めっき方法は任意であり、電気めっき法、溶融めっき法、溶融塩電解めっき法、蒸着めっき法など、公知の任意のめっき方法を採用できる。
【００６７】
基板には、塗装金属板の耐食性、塗膜密着性などの長期耐久性を向上させるために、内層塗膜（例、下塗り、中塗り）以外に、塗布型、反応型等のクロメート処理皮膜や、りん酸塩処理皮膜など、公知の塗装前処理皮膜を形成してもよい。しかし、これらの前処理皮膜は太陽熱反射性を損ない、また放射率を増大させる傾向があるので、塗装前処理皮膜の付着量は、密着性などの改善効果が得られる範囲で少ない程よい。
【００６８】
前処理皮膜の付着量は、クロメート処理皮膜であれば金属クロム換算で２００ ｍｇ／ｍ^２ 以下、より好ましくは１００ ｍｇ／ｍ^２ 以下とするのがよい。りん酸塩処理皮膜の場合の付着量は、５．０ ｇ／ｍ^２以下、より好ましくは３．０ ｇ／ｍ^２以下とするのがよい。これを超えると、太陽熱反射性を阻害するうえ、金属板を加工する際に塗膜の割れや剥離が生じることがあるので好ましくない。
【００６９】
密着性改善などの効果を得るには、前処理皮膜の付着量を、クロメート処理の場合は５ｍｇ／ｍ^２ 以上、より好ましくは２０ ｍｇ／ｍ^２以上とするのがよい。りん酸塩処理の場合は０．２ ｇ／ｍ^２以上、より好ましくは０．５ ｇ／ｍ^２以上とするのがよい。
【００７０】
基板がステンレス鋼板またはアルミニウム板である場合も、塗膜との密着性を高めるために公知のクロメート処理を施してもよく、その場合は上記の範囲の付着量とすればよい。
製造方法：
本発明の太陽熱反射性の塗装金属板の製造方法は特に限定されないが、上述した反射性顔料とバインダーの有機樹脂を溶媒中に含有させた塗料を、基板の片面または両面に塗布し、乾燥し、必要であれば熱硬化させて反射性塗膜を形成することにより製造するのが好ましい。
【００７１】
塗料に用いる溶剤については特に限定はなく、有機樹脂に合わせて、慣用の溶剤から適宜選択して用いればよい。溶媒としては、水、トルエン、キシレン、シクロヘキサノン、メチルエチルケトン等が例示されるが、これらに限られるものではない。樹脂は、溶媒に溶解していても、或いはエマルジョン樹脂のように溶媒に分散ないし懸濁しているものでもよい。塗料には、前述の体質顔料、架橋剤、分散剤等を配合させることができる。
【００７２】
塗料の塗布方法は公知の方法で行えばよく、例えば、スプレーコート、ロールコート、カーテンフローコート、バーコート等の方法が適用できる。塗装後は、熱風オーブン、誘導加熱オーブン等の公知の手法で乾燥および冷却すればよい。これらの処理は、公知の塗装設備を用いて施すことができる。
【００７３】
基板に塗料を塗布する前に、前述したように、基板には塗装前処理、下塗り、中塗りを適宜施してもよく、或いはその一部または全部を省略してもよい。さらに、中塗り用の塗料にも反射性顔料を含有させることも可能である。
【００７４】
また、裏面側は、日射面側と同じ塗装を施してもよく、或いは別の塗装を施してもよい。別の塗装に用いる顔料は、前述したように裏面側の放射率を低くするようなものを選択することが好ましい。裏面側の塗装も上記と同様に施すことができる。
【００７５】
本発明の塗装金属板は、前述したように屋根材、外壁材などの建築用外装材として最適であり、加工性にも優れているので、折り曲げ、絞り等により必要な形状に加工して製品とすることができる。
【００７６】
【実施例】
（実施例１）
基板として、厚さ０．８０ ｍｍ の冷間圧延鋼板の母材に、１２％Ｎｉ−８８％Ｚｎ合金電気めっき （付着量３０ ｇ／ｍ^２）、１０％Ｆｅ−９０％Ｚｎ合金電気めっき （付着量３０ ｇ／ｍ^２）、または５５％Ａｌ−４５％Ｚｎ合金溶融めっき （付着量６０ ｇ／ｍ^２）を施した、３種類の両面めっき鋼板 （付着量は片面当たり） を使用した。これらの基板の ０．８〜２．１ μｍの波長領域での分光反射率を分光光度計により測定し、太陽熱反射率Ｒ_{Ｅ／ＮＩＲ} を求めた結果を表１に示す。
【００７７】
基板の日射面側の塗膜に含有させる顔料として、
（１） Ｒ_{Ｅ／ＮＩＲ} が２％、平均粒子径が０．０２μｍのカーボンブラックＭＡ−１００ ［三菱化学製］（符号「ＣＢ」） 、
（２） Ｒ_{Ｅ／ＮＩＲ} が５％、平均粒子径が３μｍの鉄黒ＢＬ−１００ ［チタン工業製］（符号「ＦＢ」） 、
（３） Ｒ_{Ｅ／ＮＩＲ} が１５％、平均粒子径が０．５ μｍの複合酸化物顔料タイピロキサイドブラウン＃９２９０［大日精化工業製］（符号「ＴＢ」） 、および
（４） Ｒ_{Ｅ／ＮＩＲ} が１５％、平均粒子径が０．３ μｍの有機顔料クロモファインブラックＡ１１０３［大日精化工業製）（符号「ＡＢ」） 、
の４種類の黒色顔料を用意した。これらのうち（３） と（４） が反射性顔料であり、（１） と（２） は比較用の顔料である。
【００７８】
上記のいずれかの顔料を４０重量部、バインダーとしてポリエステル樹脂を６０重量部、メラミン系架橋剤１０重量部を配合し、溶剤の適量のシクロヘキサノンと一緒にボールミルを用いて分散混合し、塗料を調製した。
【００７９】
これらの塗料を、上記の各種の基板に、表１に示す乾燥膜厚になるようにロールコート法で塗布し、２４０ ℃で６０秒間焼き付けて、日射面側の塗膜を形成した。下塗りと中塗りは行わなかった。日射面側の塗膜はいずれもマンセル記号Ｎ−１．５ の黒色外観を有するものであった。
【００８０】
この日射面に施した各塗膜の ０．８〜２．１ μｍの波長領域での太陽熱透過率Ｔ_{Ｅ／ＮＩＲ} を、単離した塗膜を用いて分光光度計で測定した分光透過率から求めた。塗膜の単離は、酸に塗装金属板を浸漬し、金属板を溶解することにより行った。また、めっき鋼板上の各塗膜の表面の ０．８〜２．１ μｍ波長領域での太陽熱反射率Ｒ_{Ｅ／ＮＩＲ} を、分光光度計で測定した分光反射率から求めた。これらの測定結果も表１に示す。
【００８１】
一方、塗装金属板の裏面側の塗膜に含有させる顔料として、
（５） 白色酸化チタン顔料タイペークＣＲ−９０［石原産業製、平均粒子径０．４ μｍ）（符号「ＴＩ」） 、および
（６） 鱗片状アルミニウム粉０７００Ｍ［東洋アルミニウム製］（符号「ＡＬ」）
を用いた。
【００８２】
白色顔料（５） の場合は、この顔料を４０重量部、バインダーとしてポリエステル樹脂６０重量部、メラミン系架橋剤１０重量部を配合し、溶剤の適量のシクロヘキサノンと一緒にボールミルを用いて分散混合し、塗料を調製した。この塗料を各種基板に乾燥膜厚が５μｍとなるようにロールコート法で塗布し、２４０ ℃で６０秒間焼き付けて、裏面側の白色塗膜を形成した。
【００８３】
鱗片状アルミニウム粉（６） については、これを５重量部、バインダーとしてポリエステル樹脂１００ 重量部、メラミン系架橋剤１０重量部を配合し、溶剤の適量のシクロヘキサノンと一緒にボールミルを用いて分散混合し、塗料を調製した。この塗料を、各種基板に、アルミニウム粉 （アルミ顔料） の含有量が表１に示す量になるような膜厚でロールコート法で塗布し、２４０ ℃で６０秒間焼き付けて、裏面側のメタリック色の塗膜を形成した。
【００８４】
表１に、得られた塗装金属板の基板、日射面と裏面の塗膜構成を示す。
この塗装金属板の裏面側については、 ４．５〜２５μｍの波長領域での分光反射率を測定すると共に、ＪＩＳ Ｒ３１０６ に規定されるプランクの熱放射スペクトル分布において絶対温度２９３ Ｋとした場合の相対値から裏面の放射率を求めた。この値も表１に示す。
【００８５】
上記の塗装金属板から長さ：１５０ ｍｍ、幅：２００ ｍｍの試料を切り出し、図１に示すように、開口部を有する保温容器の開口部に日射面を外側に向けてはりつけ、試料を日射に曝して保温容器内部の温度上昇に及ぼす試料の影響を調査した。
【００８６】
図１に示した保温容器６は、開口部以外の側壁部は断熱性がよいように構成されており、試料は開口部に貼り付けられて、屋外で試料面に日射が同一角度で照射されるように日射に対して追従する装置 （図示せず） 上に配設される。保温容器６の内部には熱電対４が設置されており、熱電対４を外部に設けた記録計５に接続し、保温容器６の内部の温度変化を測定できるようになっている。測定された最高到達温度を表１に示す。
【００８７】
【表１】

表１からわかるように、日射面側の塗膜の外層に反射性顔料を含有させた本発明例の塗装金属板では、顔料が太陽熱反射性ではない比較例に比べて、保温容器６の内部の最高到達温度が概ね１０℃以上低くなり、良好な太陽熱反射性を示した。中でも、塗膜の太陽熱透過率Ｔ_{Ｅ／ＮＩＲ} が２５％と高く、かつ基板の太陽熱反射率Ｒ_{Ｅ／ＮＩＲ} が７３％と非常に高い試料７が、最も良好な性能を示した。
【００８８】
裏面側の塗膜における顔料の添加量は、酸化チタン（ＴＩ）が４０重量部、鱗片状アルミニウム顔料（ＡＬ）が５重量部と、後者の方がずっと少ない。そのため、ＡＬ付着量が非常に少ない試料８、９では、裏面の放射率が試料１〜７より小さくなっているが、このＡＬ顔料の付着量が０．０５ ｇ／ｍ^２ 以上では放射率が７０％以下になった。ＡＬ顔料の付着量が１．２ ｇ／ｍ^２と十分であれば、ＴＩよりなお顔料の付着量は少ないにもかかわらず、放射率は１０％と非常に小さくなった。
【００８９】
（実施例２）
本実施例では、実施例１において表１の試験番号７ （本発明例） または試験番号２ （比較例） として示した塗装金属板に基づいて、太陽熱反射性塗膜のバインダー樹脂を変更し、および／または上に耐汚染性塗膜を形成して、耐汚染性を調査した。本実施例で作製した供試材は次の通りである。
【００９０】
（１） バインダーのポリエステル樹脂の極性基の量を調整して、水に対する接触角が５５°、６５°または８５°となる太陽熱反射性塗膜を形成した以外は、試験番号７と同様の塗膜と基板からなる塗装金属板を作製した。これらを試験番号１１〜１３
（接触角は順に５５、６５および８５°） とする。
【００９１】
（２） バインダーの有機樹脂として、ポリエステル樹脂に代えて、フッ素樹脂を用いた以外は試験番号７と同様の塗膜と基板からなる塗装金属板を作製した （試験番号１４） 。この塗膜表面の水に対する接触角は９５°であった。
【００９２】
（３） 試験番号７で得た太陽熱反射性塗膜の上に、水に対する接触角が５５°の皮膜を形成できるポリエステル樹脂塗料を乾燥膜厚が３μｍになるように塗装し、乾燥して、クリアー塗膜を形成した （試験番号１５） 。
【００９３】
（４） 試験番号７で得た太陽熱反射性塗膜の上に、フッ素樹脂塗料を乾燥膜厚が３μｍになるように塗装し、乾燥して、水に対する接触角が９５°のクリアー塗膜を形成した （試験番号１６） 。
【００９４】
（５） バインダーのポリエステル樹脂の極性基の量を調整して、水に対する接触角が５５°または６５°となる太陽熱反射性塗膜を形成した以外は、試験番号２と同様の塗膜と基板からなる塗装金属板を作製した。これらを試験番号１７および１８とする。
【００９５】
以上の試験番号１１〜１８の塗装金属板の供試材を、水平面から４５°傾斜させて、屋外に３カ月間曝露した後、表面の汚れを落とさず、そのままの状態で、曝露面を上面にして、図１に示すように、保温容器６の上面に貼り付け、実施例１に説明したように屋外にて日射に曝して容器内の温度上昇を測定した。表２に最高到達温度を、塗装金属板の反射率と一緒に示す。
【００９６】
【表２】

表２からわかるように、本発明例である試験番号７をベースにした、試験番号１１〜１６の塗装金属板は、表面の水に対する接触角に関係なく、いずれも試験番号７のものと同様に太陽熱反射性が高く、保温容器内の温度上昇が低く、遮熱性に優れていた。一方、比較例である試験番号２をベースにした塗装金属板は、試験番号２と同様に、太陽熱反射性が低く、遮熱性に劣っていた。即ち、耐汚染性を付与するためのバインダー樹脂の変更やクリアー塗膜の上塗りは、太陽熱反射性には著しい影響を及ぼさない。
【００９７】
耐汚染性に関しては、表面の水に対する接触角が６０°以下または９０°以上である試験番号１１、１４、１５、１６および１７では、基本となる表１の試験番号７（表２の試験番号１１〜１６の場合）または試験番号２（表２の試験番号１７〜１８の場合） に比べて、３カ月の屋外暴露後の遮熱性の低下が小さく、耐汚染性がよいために、汚染物質の付着が少なく、太陽熱反射性の低下、従って遮熱性の低下が少なかったことがわかる。一方、この接触角が６５°または８５°であった試験番号１２、１３、１８では、屋外暴露後の遮熱性の低下が大きく、上記に比べて耐汚染性が劣っていたことがわかる。
【００９８】
【発明の効果】
本発明の太陽熱反射性の高い塗装金属板は、主として屋根などの建材用外装材として最適であり、屋根の要求性能である軽量性と遮熱性に優れ、自由な色に着色でき、しかも生産性よく安価に製造できる。また、日射面に耐汚染性を付与することで、汚染による太陽熱反射性の低下を抑制することができ、長期にわたって遮熱性を保持する。
【図面の簡単な説明】
【図１】表面処理金属板の反射性を測定する装置の断面図である。
【符号の説明】
１：太陽光、２：反射層、３：基板、４：熱電対、
５：記録計、６：保温容器[0001]
TECHNICAL FIELD OF THE INVENTION
TECHNICAL FIELD The present invention relates to a coated metal plate that is excellent in solar heat reflectivity, is preferably used as a building exterior material such as a roofing material, and suppresses a rise in the temperature of a substrate and the dissipation of heat to the back surface when receiving solar radiation.
[0002]
[Prior art]
The structural reinforcement of houses is being promoted from the viewpoint of improving disaster prevention, etc., and as a part thereof, weight reduction of roof materials is desired. Roof materials include new ceramics, metal roofs, etc. in addition to Japanese tiles.
[0003]
Metal roofs are about 1/10 the weight of Japanese roof tiles, and about 1/3 the weight of new ceramics, and are considered to be the preferred materials for promoting structural reinforcement and weight reduction. . However, metal has higher thermal conductivity than ceramic materials, so metal roofing material has the drawback that solar heat easily conducts to the attic and is dissipated into the room from the back side, increasing the indoor temperature. .
[0004]
As a method of suppressing the influence of solar heat, there is a method of bonding a heat insulating material to the back surface of a metal roofing material. However, usually, a method of bonding a heat insulating material after forming a metal plate is adopted, so that the manufacturing process of the bonding material is complicated, and initial costs required for dedicated equipment are high, so that economical efficiency is high. There is a problem that lacks.
[0005]
There is also a method of applying a heat-insulating heat-insulating paint to metal roofing materials.However, the heat-insulating heat-insulating paint is a special paint that uses a ceramic having a large number of hollow bubbles as a pigment. It is necessary to be thick, and there is a problem that economic efficiency and designability are impaired. For this reason, it has not yet been widely adopted for general use.
[0006]
Japanese Patent Application Laid-Open No. 5-293434 discloses an automobile body or an automobile part coated with a low-brightness solar heat-shielding top coat obtained by combining a plurality of pigments having a constant solar heat reflectance and performing additive color mixing. Have been. This technique enhances solar heat reflectivity by a top coat having excellent heat reflectivity. However, it is not always possible to sufficiently secure the solar heat shielding property by using only the coating film, and the color is also limited to a dark tone having low brightness.
[0007]
In the above publication, when the solar heat shielding property is insufficient, it is better to use an aluminum base having good heat shielding property, but aluminum has low strength, welding is difficult, and material cost is extremely high Therefore, there is a problem in widely adopting a roof material for general use. Furthermore, even if an aluminum base is employed, the reflectance of the base may be low depending on the type and amount of the added element, the surface roughness and the oxide film thickness, and the solar heat reflectivity may be poor when the above coating is applied. .
[0008]
[Problems to be solved by the invention]
INDUSTRIAL APPLICABILITY The present invention is suitable for architectural exterior materials such as roofs, has excellent solar heat reflectivity, can suppress indoor temperature rise, can be painted in any color, is economical, and is versatile. A painted metal plate is provided.
[0009]
[Means for Solving the Problems]
In a building, its landscape and design are evaluated as important factors. For this reason, it is necessary for a painted metal plate used as a building exterior material to be able to freely color any color or pattern.
[0010]
Most of the solar heat is emitted as visible light or near infrared light having a wavelength of 0.3 to 2.1 μm. Therefore, it is desirable that a painted metal plate used as a building exterior material has a high solar heat reflectance so as not to absorb solar heat as much as possible.
[0011]
From the above viewpoints, the present inventors have studied in detail the influence of a substrate and a coating film on the solar heat reflectivity of a coated metal plate obtained by coating a metal substrate. As a result, the following knowledge was obtained regarding effective prevention of temperature rise due to solar heat.
[0012]
a. The color, gloss, and the like of the object are substantially determined by the outer coating film among the coating films. Further, since the color is visually recognized, it is determined by the reflectance of light from the object surface at a wavelength (0.38 to 0.78 μm) in the visible light region. That is, the reflectance of solar heat in the visible light region is determined by the color. Therefore, unless the color of the outer layer coating is changed, it is difficult to change the amount of solar heat absorption or reflectance in the visible light region of the outer layer coating.
[0013]
However, by increasing the reflectance in the near infrared region (0.8 to 2.1 μm) outside the visible light region of the outer layer coating film, the color of the object surface can be colored in a desired color, and the solar thermal reflectivity can be improved. Can be improved. To achieve this, it is effective to make the outer layer coating film contain a certain amount or more of a pigment having a solar heat reflectance of 10% or more in the near infrared region. Hereinafter, such a pigment having good solar heat reflectivity is also simply referred to as “reflective pigment”, and a coating film having high solar heat reflectance containing this reflective pigment is also referred to as “reflective coating film”.
[0014]
In the coating of metal plates, an undercoating film (primer) is placed between the outer coating film and the substrate for the purpose of improving the adhesion of the outer coating film and improving the rust resistance and finish of the coated metal plate. Or an intermediate coating film (hereinafter, these are also simply referred to as “inner coating film”) in some cases.
[0015]
When the metal plate has a plurality of coating films as described above, two or more coating films may be used as the reflective coating films. The most effective way to improve solar heat reflectivity is to include a reflective pigment in the outer layer coating film. However, for example, in the case where the outer layer coating is thin and the concealing property is not sufficient even when the reflective pigment is contained, in addition to the outer layer coating, at least one inner layer coating also includes the reflective pigment. In a suitable amount, a coated metal plate having sufficient solar heat reflectivity can be obtained.
[0016]
The reflective pigment to be contained in the inner layer coating film whose color does not appear to the outside is a pigment having a solar heat reflectance of 10% or more at a wavelength in the visible light region (0.38 to 0.78 μm) in addition to the near infrared region. It is more effective to use.
[0017]
b. Some metal substrates have excellent solar heat reflectivity. When using such a substrate, if the solar heat transmittance in the near infrared region of the coating film is increased, it is possible to obtain a coated metal plate having high solar heat reflection by utilizing the solar heat reflection from the substrate. It becomes.
[0018]
As a coating film with high solar heat transmittance, there is a clear coating film that does not contain pigments.However, since the color of the substrate appears outside, the design of the coated metal plate is lacking, and other performance such as corrosion resistance is also insufficient. Tends to. When using a pigment with low absorption in the near infrared region and high transmittance and adjusting the film thickness and pigment content of the coating film, even a pigment-containing coating film has a high solar heat transmittance in the near infrared region. A coating can be formed. By forming the coating film having high solar heat transmittance on the surface of the metal substrate having high solar heat reflectance, a coated metal plate having high solar heat reflectance can be obtained.
[0019]
Specifically, the solar thermal reflectance (R _{E / NIR} ) Is 40% or more, and the solar heat transmittance (T _{E / NIR} ) Is 20% or more to form a pigment-containing coating film having a high solar heat transmittance.
[0020]
Solar heat reflectance (R _{E / NIR} ) Can be easily obtained by plating the surface of the material with excellent solar heat reflectivity. Above all, a material provided with a plating film containing 50% by mass or more of aluminum has good solar heat reflectivity, and is also excellent in corrosion resistance and economy, and thus is suitable as a building material.
[0021]
c. When a painted metal plate is used as a building exterior material, the solar heat absorbed by it will be transferred by the convection of the indoor air and the surface on the side opposite to the solar radiation (hereinafter, the opposite side is referred to as the “back side”). It is transmitted into the room by the radiation from and increases the indoor air temperature. Therefore, if the radiation from the back surface into the room is suppressed, it is possible to further suppress the rise in the indoor air temperature. For that purpose, the emissivity of the back surface may be reduced.
d. The undercoating film and the intermediate coating film, which are the inner coating films, are usually coating films containing a pigment that easily absorbs solar heat. Therefore, when the inner layer coating film is not a reflective coating film containing a reflective pigment, it is desirable that the inner layer coating film is thinner from the viewpoint of the solar heat reflectivity of the coated metal plate.
[0022]
In addition, when a painted metal plate is applied to a building exterior material, a substrate is often subjected to a pre-coating treatment in order to improve long-term durability such as corrosion resistance and coating film adhesion. Chromate treatment, phosphate treatment and the like are generally used as pretreatments for coating, but these compounds have absorption in the visible and infrared regions. Therefore, it is preferable that the amount of adhesion in the pre-coating treatment is small.
[0023]
e. If contaminants from the outside adhere to the surface that receives solar radiation, the reflection performance may be reduced. Therefore, it is desirable that the surface receiving the solar radiation has a surface excellent in stain resistance. To keep the solar surface clean, it is necessary to reduce the contact angle of the solar surface with water to increase the surface wettability and make it easier for contaminants to run down during rainfall. It is effective. Conversely, it is also effective to prevent the contaminants that may be contained in raindrops from adhering to the surface exposed to sunlight by making the surface of the sunshine hydrophobic so that raindrops do not adhere during rainfall It is.
[0024]
The present invention completed on the basis of the above findings is, in the broadest sense, a coated metal plate obtained by applying a coating to a metal substrate and having a wavelength range of 0.8 to 2.1 μm on the surface that receives solar radiation (that is, Solar thermal reflectance (R) in the near infrared region) _{E / NIR} ) Is not less than 20%, and is a coated metal plate in which the temperature rise of the substrate due to solar radiation is suppressed.
[0025]
In one embodiment, the coated metal plate has a solar thermal reflectance (R) in a wavelength region of 0.8 to 2.1 μm on a surface receiving solar radiation. _{E / NIR} ) Contains at least one layer of a solar heat reflective coating containing 2% to 70% by mass of a pigment (i.e., a reflective pigment) of 10% or more.
[0026]
In another embodiment, the coated metal sheet has a solar thermal reflectance (R) in a wavelength range of 0.8 to 2.1 μm on the surface of the metal substrate that receives the solar radiation. _{E / NIR} ) Is 40% or more, and the surface has a solar heat transmittance (T) in a wavelength region of 0.8 to 2.1 μm. _{E / NIR} ) Is 20% or more. A preferred substrate in this case is a plated metal plate provided with a plated film containing 50% by mass or more of aluminum.
[0027]
Note that the above two aspects can coexist. That is, it is a reflective coating film containing 2 to 70% by mass of a reflective pigment, and has a solar heat transmittance (T _{E / NIR} ) Is 20% or more. In that case, the solar thermal reflectance (R _{E / NIR} ) Is higher than 40%, the high solar heat reflectivity of the coating film and the high solar heat reflectivity of the substrate are combined, so that the solar heat reflectivity is very high and the heat dissipation to the back side is greatly suppressed. A painted metal plate is obtained.
[0028]
When the coated metal plate has two or more coating films, it is preferable that at least the outer layer is the above-mentioned solar heat reflective coating film, and the thickness of the coating film on the inner side is 200 μm or less.
Preferably, the emissivity of the surface of the painted metal plate opposite to the surface that receives solar radiation is 70% or less. The outer layer coating film on the opposite side was coated with a scale-like aluminum pigment at 0.05 to 1.5 g / m2. ² It is preferred to contain.
[0029]
It is preferable that the surface receiving the sun has a contact angle with water of 60 ° or less or 90 ° or more in order to enhance the stain resistance. When the surface of the surface receiving the solar radiation is a solar heat reflective coating, this coating can be a coating having a contact angle to water of 60 ° or less or 90 ° or more. Alternatively, a pollution resistance can be imparted by overcoating a film having a contact angle to water of 60 ° or less or 90 ° or more and a thickness of 0.5 to 50 μm on the solar heat reflective coating film. .
[0030]
In the present invention, the solar thermal reflectance used for the surface of the coated metal plate which receives the sunlight, the pigment, and the substrate is the solar thermal reflectance in consideration of the intensity of the spectrum in the wavelength region calculated from the spectral reflectance (Rλ). It is. Solar thermal reflectance in the wavelength range of 0.8 to 2.1 μm (R _{E / NIR} ) Is calculated by the following equation (1).
[0031]
(Equation 1)

R _{E / NIR} : Solar heat reflectance (%) in a wavelength range of 0.8 to 2.1 μm,
Eλ: spectral intensity of solar heat,
Rλ: spectral reflectance (measured with a spectrophotometer).
[0032]
The solar heat transmittance of the coating film is a solar heat transmittance in consideration of the intensity of the spectrum in the wavelength region calculated from the spectral transmittance (Tλ) of the coating film. Solar heat transmittance of the coating film in the wavelength range of 0.8 to 2.1 μm (T _{E / NIR} ) Is obtained by the following equation (2).
[0033]
(Equation 2)

T _{E / NIR} : Solar heat transmittance (%) of the coating film in a wavelength region of 0.8 to 2.1 μm,
Eλ: spectral intensity of solar heat,
Rλ: spectral transmittance (measured with a spectrophotometer).
[0034]
In the present invention, the emissivity of the back surface is a relative value in the case where the absolute temperature is 293K in the Planck thermal radiation spectrum distribution, which is calculated from the spectral reflectance (Rλ) of the back surface in a wavelength region of 4.5 to 25 μm. Emissivity. The emissivity α is obtained by the following equation (3).
[0035]
(Equation 3)

α: emissivity (%),
Gλ: relative value when Plan Absolute temperature is 293K in Planck's thermal emission spectrum distribution;
Rλ: spectral reflectance (measured with a spectrophotometer).
[0036]
BEST MODE FOR CARRYING OUT THE INVENTION
The coated metal plate of the present invention is one in which at least one surface of a metal substrate that receives solar radiation is coated, and a wavelength region of 0.8 to 2.1 μm of a surface that receives solar radiation (hereinafter, also referred to as a solar radiation surface). = Solar thermal reflectance (R) _{E / NIR} ) Is 20% or more. R on the solar surface _{E / NIR} Is less than 20%, the effect of suppressing the temperature rise of the substrate as the solar heat reflective coated metal plate is reduced. R on the solar surface _{E / NIR} Is preferably at least 30%.
[0037]
In one embodiment, the coated metal plate has a solar heat reflectance (R _{E / NIR} ) Is 10% or more, and at least one reflective coating film containing 2 to 70% by mass of a pigment (that is, a reflective pigment) may be provided on the solar radiation surface. When the painted metal plate has a plurality of coating films on the solar radiation surface, it is preferable that at least the outer coating film is a reflective coating film. That is, only the outer coating film may be a reflective coating film, or a part or all of the inner coating film may be a reflective coating film. In the case where the outer layer coating is thin and the concealing property is not sufficient even if the reflective pigment is contained, the inner layer coating may also contain the reflective pigment.
[0038]
The outer layer coating film in the present invention means a coating film applied in a coating step for determining the color of a coated metal plate. For the purpose of improving performance such as stain resistance, a clear film may be further provided on the outer layer coating film, but in the present invention, the clear film is not considered to be the outer layer coating film.
[0039]
In another embodiment, the coating on the sunlit surface has a solar thermal transmittance (T) in the wavelength range of 0.8 to 2.1 μm. _{E / NIR} ) Is a pigment-containing coating film having a high solar heat transmittance of not less than 20%, and a solar heat reflectance (R) in a wavelength region of at least 0.8 to 2.1 μm of at least a surface of the metal substrate which receives sunlight. _{E / NIR} ) Is as high as 40% or more. In this case, since the solar heat reflected from the substrate is reflected to the outside through the coating film, the coated metal plate can exhibit high solar heat reflectivity.
[0040]
In the present invention, the reflectance of the solar radiation surface of the coated metal plate, the reflectance of the reflective pigment used for the coating film, and the solar heat transmittance of the coating film are all in the near infrared region of 0.8 to 2.1. solar thermal reflectance (R for wavelengths in the μm wavelength region _{E / NIR} ) Or solar heat transmittance (T _{E / NIR} ) Is because the solar heat reflectance and the solar heat transmittance with respect to the wavelength in the visible light region are determined depending on the color. If the solar heat reflectance and the solar heat transmittance are specified for the wavelength in the visible light region, the degree of freedom of the color of the painted metal plate is lost, and the coated metal plate is not suitable as a building exterior material. According to the present invention, it is possible to remarkably suppress a rise in the substrate temperature when receiving solar radiation simply by defining the solar heat reflectance and the solar heat transmittance with respect to the wavelength in the near infrared region.
Paint film :
(1) Reflective coating
The reflective coating film provided on the solar radiation surface of the coated metal plate contains 2 to 70% by mass of a reflective pigment having a solar heat reflectance of 10% or more in the near infrared region as described above (dry weight of the coating film) The same applies hereinafter). If the content of the reflective pigment (when two or more reflective pigments are used in combination) is less than 2% by mass in the coating film, the metal plate should have sufficient solar heat reflectivity. In addition, a thick film coating is required to obtain a desired color due to insufficient coloring power. This content is preferably at least 5% by mass. When the content of the reflective pigment exceeds 70% by mass in the coating film, the processability of the coating film is impaired. The upper limit of the content is preferably 60% by mass.
[0041]
The number of the reflective pigments contained in the reflective coating film is not limited to one, and one or two or more pigments satisfying the above conditions can be arbitrarily selected in consideration of hue, weather resistance, and color stability. . When two or more kinds of reflective pigments are used, their total content may be within the above range.
[0042]
It is desirable that the reflective pigment used in the coated metal plate of the present invention is safe, has excellent water resistance and weather resistance, and maintains a heat shielding effect for a long period of time. Among them, it is preferable to use pigments selected from metal compounds such as metal oxides, sulfides and chromates, insoluble dyes (dye pigments), lake pigments and the like.
[0043]
If the average particle size of the pigment exceeds 50 μm, the solar heat reflectivity is poor. Therefore, the average particle size of the reflective pigment is preferably 50 μm or less. From the viewpoints of stain resistance, weather resistance, and color stability, the average particle size of the reflective pigment is more preferably 20 μm or less, and still more preferably 10 μm or less.
[0044]
In the reflective coating film, in addition to the above-mentioned reflective pigment, a color pigment necessary for obtaining a desired color, concealing property, coating performance such as corrosion resistance, a rust-preventive pigment, and a substrate surface and an organic binder serving as a binder. For the purpose of increasing the adhesion to a resin (for example, a polyester resin, a fluororesin, etc.), the cohesive strength of the coating film itself, and improving the concealment and brightness of the base, for example, silica, alumina, calcium carbonate, barium sulfate, An extender such as kaolin, clay, talc, nepheline, sinite, mica, and a bubble-containing pigment may be contained.
[0045]
As a binder that holds pigments, it does not easily cause yellowing, discoloration, decrease in gloss, and chalking even when exposed to sunlight. It is preferable to use an organic resin that can be used.
[0046]
Examples of such a resin include various organic resins such as an acrylic resin, a polyester resin, a polyolefin resin, and a fluorine-based resin, and any one of them may be used. It may be used. The content of these organic resins is preferably in the range of 10 to 90% by mass of the coating film as a solid content.
[0047]
In the resin, thickeners such as synthetic finely divided silica, organic bentonite, carboxymethylcellulose, polyvinyl alcohol, etc., crosslinkers such as melamine, benzoguanamine, isocyanate, dispersants such as polyacrylic acid, polyacrylate, etc. A dirty photocatalyst or the like may be contained.
[0048]
The thickness of the reflective coating is preferably in the range of 3 to 200 μm. A coating film thinner than 3 μm may not have stable hue. The thickness of this coating film is more preferably 7 μm or more. When the thickness of the coating film exceeds 200 μm, peeling or cracking of the coating film may occur during processing, and a plurality of coating operations are required, resulting in poor economic efficiency. More preferably, it is 50 μm or less.
[0049]
The undercoating film or the intermediate coating film as the inner coating film usually contains a pigment which easily absorbs solar heat. Therefore, when the content of the reflective pigment in these inner layer coating films is less than 2%, the thickness is preferably thinner so as not to impair the solar heat reflectivity, and is preferably 200 μm or less. More preferably, it is 50 μm or less.
[0050]
The outer layer coating of the coated metal plate of the present invention may be a metallic coating by mixing aluminum flakes (flaky aluminum pigment) with a coating to be used, or a matte coating by mixing a matting agent. A design property can be imparted. Also, the reflective coating is preferably provided as the outer layer coating of the coated metal plate of the present invention, that is, as the uppermost layer. For example, in the case of a metallic coating containing aluminum flakes, the reflective coating is optionally provided. A clear layer containing no pigment or a translucent layer containing a small amount of pigment may be provided on the film.
(2) Solar heat transmittance (T _{E / NIR} ) 20% or more coating film
The coating film in this case also has a T of 20% or more. _{E / NIR} Basically, the same as the above-mentioned solar heat reflective coating, except that the coating is configured so that the solar heat absorption in the near infrared region of 0.8 to 2.1 μm is not increased in order to ensure Is fine.
[0051]
As the pigments, there are pigments of the types listed for the reflective pigments. Among them, pigments having a low light absorption in the near infrared region and a high transmittance may be used. If the average particle size or the coating thickness of the pigment is too large, the solar heat transmittance of the coating decreases, so the average particle size of the pigment is preferably 20 μm or less, and the coating thickness is in the range of 1 to 100 μm. Is preferred. It is preferable that the organic resin used as the binder and the additive to be present in the coating film be selected so as not to hinder the solar heat transmittance in the near infrared region of the coating film.
[0052]
As described above, even if a reflective coating film contains a reflective pigment in an amount of 2 to 70% by mass, if the type, particle size, coating film thickness, and other conditions of the pigment are appropriately selected, T _{E / NIR} Is 20% or more.
(3) Stain resistant coating
As described above, if contaminants adhere to the insolated surface of the coated metal sheet of the present invention and become contaminated, the solar heat reflectivity decreases and the desired heat shielding performance also decreases. Therefore, it is advantageous to impart stain resistance to the surface of the solar radiation surface for long-term performance retention.
[0053]
Most of the contaminants that adhere to painted metal plates used outdoors are hydrophobic substances. Therefore, in order to suppress contamination of the solar radiation surface, it is preferable to improve the water wettability of the surface of the solar radiation surface so that hydrophobic contaminants are hardly attached. If the water wettability of the surface is improved, hydrophobic contaminants cannot strongly adhere to the surface and are easily washed away during rainfall, so that no contaminants accumulate. In order to ensure such water wettability, the contact angle of water on the surface of the solar radiation surface may be 60 ° or less. A hydrophilic coating film having a contact angle to water of 60 ° or less can be obtained by using a hydrophilic organic resin having a polar group such as a hydroxyl group or a carbonyl group as a part or all of a binder. In order to adjust the contact angle, the type and amount of the polar group of the resin may be changed, or two or more resins may be used in combination.
[0054]
Conversely, to prevent contaminants that may be contained in raindrops during rainfall from adhering to the insolation surface, the surface of the insolation surface is made hydrophobic, making it difficult for raindrops to adhere to the insolation surface. This is an effective way to prevent surface contamination. For this purpose, it is preferable that the contact angle of the surface of the solar radiation surface with water is 90 ° or more. A hydrophobic coating film having a water contact angle of 90 ° or more can be obtained by using a non-polar organic resin such as a polyolefin resin or a fluororesin as a binder.
[0055]
When imparting stain resistance to the coated metal plate of the present invention by the above-mentioned means, the binder resin of the outer solar reflective coating film appearing on the surface is changed to a hydrophilic or hydrophobic resin, and the contact angle of the coating film to water is adjusted to water. Is 60 ° or less or 90 ° The above may be adopted. That is, stain resistance is imparted to the outer solar reflective coating film itself. However, in this method, the kind of the binder resin used for the solar heat reflective coating film is limited, so that the cost may be increased and other performances such as workability and corrosion resistance may not reach desired levels.
[0056]
In another aspect, the contact angle with water is 60 ° or less or 90 ° on the solar heat reflective coating. ° A stain-resistant coating film having the above surface can be separately formed. This stain-resistant coating film can be formed using a hydrophilic or hydrophobic binder resin as described above. In this case, the thickness of the stain-resistant coating film is preferably 0.5 to 50 μm. If the thickness is less than 0.5 μm, the effect of improving the stain resistance is small, and if it exceeds 50 μm, the solar heat reflectivity may be impaired. The stain-resistant coating film may be a clear coating film that does not contain a pigment, but may contain a pigment as long as it does not impair solar heat reflectivity or solar heat permeability.
(4) Backside coating
The coated metal plate of the present invention only needs to have the above-mentioned reflective coating film or solar heat permeable coating film on only one side of the substrate on the side to be the solar radiation surface. There is no particular limitation on the surface (rear surface) of the substrate facing the room opposite to the solar radiation surface. The back surface is not necessarily a painted surface, but is preferably a surface having an emissivity of 70% or less.
[0057]
When a painted metal plate is used as a building exterior material, the absorbed solar heat is transmitted into the room by conduction by convection of room air and radiation from the back surface, thereby increasing the room air temperature. Therefore, if the radiation from the back surface to the room is suppressed, it is possible to suppress an increase in the indoor air temperature. That is, the emissivity of the back surface may be reduced.
[0058]
The emissivity can be obtained from the measurement of the spectral reflectance and the above equation (3). If the emissivity of the back surface exceeds 70%, the temperature rises significantly at room temperature. Therefore, it is advantageous to set the emissivity to 70% or less, particularly 50% or less.
[0059]
In order to reduce the emissivity of the back surface, a clear coating is applied to the metal surface of the back surface, or a coating containing a total of 2 to 70% by mass of one or more of the above-described reflective pigments as an outer layer coating film (i.e., , Or the same paint as that on the solar radiation side) or paint with aluminum paint is effective.
[0060]
The aluminum paint is a paint containing a flaky aluminum pigment, and a coating film containing 2 to 30% by mass of the flaky aluminum pigment is suitable. Scaly aluminum pigments can be less radioactive than other pigments when compared at the same content. The thickness of the coating film having a small emissivity is preferably in the range of 1 to 20 μm. In that case, the content of the flaky aluminum pigment in the coating film is 0.05 to 1.5 g / m. ² Is preferably within the range. This content is 0.05 g / m ² If it is smaller, a sufficiently low emissivity cannot be obtained, and 1.5 g / m ² Exceeding the range may cause peeling or cracking of the coating film during processing.
[0061]
The coating film on the back side having a small emissivity may contain a coloring pigment, a rust-preventive pigment, or an extender pigment in addition to the above-described pigment, as described for the reflective coating film. Further, as the binder for holding the pigment, it is preferable to use the same organic resin as the reflective coating film. Further, an additive such as a dispersant may be contained similarly to the reflective coating film.
substrate :
As the metal substrate, any metal plate having characteristics required for the intended use can be used, and the type and chemical composition are not particularly limited. For example, a low-alloy steel, a high-carbon steel, a steel plate made of a low-alloy steel used for a high-strength steel plate, a plated steel plate using these steel plates as a base material, a stainless steel plate, an aluminum plate, and the like are exemplified.
[0062]
When the coating film formed on the solar radiation surface of the substrate is a reflective coating film, it is possible to obtain a coated metal plate having high solar heat reflectivity regardless of the type of the substrate. Therefore, the substrate may be selected in consideration of characteristics required for the coated metal plate such as corrosion resistance and strength. In this case, preferred substrates are plated steel sheets, particularly Zn-based plated steel sheets (pure Zn-plated or Zn-based alloy plated steel sheets) and Al-based plated steel sheets having excellent corrosion resistance. However, as described later, the T _{E / NIR} Is higher than 20%, it is possible to obtain a coated metal plate having a higher solar heat reflectivity by selecting a substrate having a higher solar heat reflectivity.
[0063]
Even if a coating film containing a reflective pigment is formed on the solar radiation surface of the substrate, depending on the thickness of the coating film and the content of the pigment, the hiding power of the coating film in the near infrared region is insufficient, and the solar heat reflection Solar reflective properties as a functionally coated metal plate may not be sufficient. This is because near infrared rays have higher transmittance of the coating film than visible light rays. In such a case, it is effective to use a substrate having good solar heat reflectivity in the near infrared region as a substrate and to enhance the reflectivity of the coated metal plate by utilizing the solar heat reflectivity from the substrate. As described above, in the case of using a metal substrate having high solar heat reflection and obtaining a coated metal plate having high solar heat reflection by utilizing reflection from the substrate, the coating film should have a solar heat transmittance T. _{E / NIR} Is 20% or more. If this coating is solar heat reflective, the solar heat reflectivity of the coated metal plate is further enhanced.
[0064]
Specifically, the solar heat transmittance (T) of the coating film formed on the solar radiation surface in the wavelength region of 0.8 to 2.1 μm _{E / NIR} ) Is 20% or more, the solar heat reflectivity is greatly affected by the reflectivity of the substrate. In that case, the solar thermal reflectance (R _{E / NIR} ) Is 40% or more, a coated metal plate having high solar heat reflection on the solar radiation surface is obtained. R _{E / NIR} Is less than 40%, the reflectivity of the painted surface on the solar radiation side decreases. Preferably, the R _{E / NIR} Is at least 50%, more preferably at least 60%.
[0065]
When the substrate is a plated steel sheet, the type of plating is not particularly limited, but the substrate has good reflectivity to sunlight, and the R _{E / NIR} Is preferably 40% or more, and from the economical efficiency of the plating operation, Al-Zn-based, Al-Mn-based, Al-Si-based and the like are suitable. Among them, those provided with a plating film containing 50% by mass or more of aluminum are preferable, and pure aluminum plating may be used. The plating film may further contain an appropriate amount of an alloy element such as Ni, Cr, Fe, or Co. Such a plating film has a feature that it has high solar heat reflectivity and also has excellent corrosion resistance and economic efficiency of the substrate. In addition, even in the case of a Zn-based plated steel sheet, R _{E / NIR} May be 40% or more.
[0066]
The adhesion amount of the plating film is optional, but a plating film having a thickness of 0.01 μm or more is preferable because the solar heat reflectivity is improved. The plating method is optional, and any known plating method such as an electroplating method, a hot-dip plating method, a molten salt electrolytic plating method, and a vapor deposition plating method can be adopted.
[0067]
In order to improve the long-term durability of the coated metal plate such as corrosion resistance and coating film adhesion, in addition to the inner layer coating film (eg, undercoating, intermediate coating), chromate-treated films such as coating type and reactive type A known coating pretreatment film such as a phosphate treatment film may be formed. However, since these pretreatment films tend to impair the solar heat reflectivity and increase the emissivity, the amount of the pretreatment film applied is preferably as small as possible within a range where the effect of improving the adhesion and the like can be obtained.
[0068]
The amount of the pre-treated film is 200 mg / m in terms of metal chromium if it is a chromate-treated film. ² Or less, more preferably 100 mg / m ² It is better to do the following. The amount of adhesion in the case of a phosphate treatment film is 5.0 g / m ² Or less, more preferably 3.0 g / m ² It is better to do the following. Exceeding the above range is not preferable because the solar heat reflectivity is impaired and the coating film may be cracked or peeled off when processing the metal plate.
[0069]
In order to obtain an effect such as improvement in adhesion, the amount of the pretreatment film to be applied should be 5 mg / m in the case of chromate treatment. ² Or more, more preferably 20 mg / m ² It is better to do the above. 0.2 g / m2 for phosphate treatment ² Or more, more preferably 0.5 g / m ² It is better to do the above.
[0070]
Even when the substrate is a stainless steel plate or an aluminum plate, a known chromate treatment may be applied in order to enhance the adhesion to the coating film. In this case, the amount of adhesion may be in the above range.
Production method :
The method for producing the solar heat-reflective coated metal sheet of the present invention is not particularly limited.A paint containing the above-described reflective pigment and the organic resin of the binder in a solvent is applied to one or both surfaces of the substrate, and dried. Preferably, it is produced by thermosetting, if necessary, to form a reflective coating film.
[0071]
The solvent used for the paint is not particularly limited, and may be appropriately selected from conventional solvents according to the organic resin. Examples of the solvent include, but are not limited to, water, toluene, xylene, cyclohexanone, and methyl ethyl ketone. The resin may be dissolved in a solvent or dispersed or suspended in a solvent such as an emulsion resin. The above-mentioned extender, a cross-linking agent, a dispersant, and the like can be blended in the paint.
[0072]
The coating method of the paint may be a known method, and for example, a method such as spray coating, roll coating, curtain flow coating, bar coating and the like can be applied. After coating, drying and cooling may be performed by a known method such as a hot air oven or an induction heating oven. These treatments can be performed using known coating equipment.
[0073]
Before applying the coating material to the substrate, as described above, the substrate may be appropriately subjected to a pre-coating treatment, an undercoat, an intermediate coat, or a part or all thereof may be omitted. Furthermore, it is also possible to include a reflective pigment in the intermediate coating.
[0074]
Further, the back side may be provided with the same coating as the solar radiation side, or may be provided with another coating. As described above, it is preferable to select a pigment used for another coating so as to lower the emissivity on the back side as described above. The coating on the back side can be applied in the same manner as described above.
[0075]
As described above, the coated metal sheet of the present invention is most suitable as a building exterior material such as a roof material and an outer wall material, and has excellent workability. It can be.
[0076]
【Example】
(Example 1)
As a substrate, a 12% Ni-88% Zn alloy electroplated on a base material of a cold rolled steel sheet having a thickness of 0.80 mm (adhesion amount: 30 g / m2) ² ) 10% Fe-90% Zn alloy electroplating (adhesion amount 30g / m ² ), Or hot-dip plating of 55% Al-45% Zn alloy (adhesion amount 60 g / m ² ), Three types of double-sided plated steel sheets (the amount of coating per one side) were used. The spectral reflectance of these substrates in the wavelength range of 0.8 to 2.1 μm was measured by a spectrophotometer, and the solar thermal reflectance R was measured. _{E / NIR} Are shown in Table 1.
[0077]
As a pigment to be contained in the coating film on the solar radiation side of the substrate,
(1) R _{E / NIR} Is carbon black MA-100 [manufactured by Mitsubishi Chemical Corporation] having a mean particle size of 0.02 μm (symbol “CB”),
(2) R _{E / NIR} Is 5% and the average particle diameter is 3 μm. Iron black BL-100 [manufactured by Titanium Industry Co., Ltd.] (symbol “FB”),
(3) R _{E / NIR} Is 15% and the average particle diameter is 0.5 μm.
(4) R _{E / NIR} , An organic pigment Chromofine Black A1103 (manufactured by Dainichi Seika Kogyo) having an average particle diameter of 15% and an average particle diameter of 0.3 μm (symbol “AB”)
Were prepared. Of these, (3) and (4) are reflective pigments, and (1) and (2) are comparative pigments.
[0078]
40 parts by weight of any of the above pigments, 60 parts by weight of a polyester resin as a binder, and 10 parts by weight of a melamine-based cross-linking agent are mixed and dispersed and mixed together with an appropriate amount of a solvent, cyclohexanone, using a ball mill to prepare a paint. did.
[0079]
These paints were applied to the above-mentioned various substrates by a roll coating method so as to have a dry film thickness shown in Table 1, and were baked at 240 ° C. for 60 seconds to form a coating film on the solar radiation side. No undercoat or intermediate coat was performed. Each of the coating films on the solar radiation side had a black appearance of Munsell symbol N-1.5.
[0080]
Solar heat transmittance T of each coating film applied to this solar radiation surface in a wavelength region of 0.8 to 2.1 μm _{E / NIR} Was determined from the spectral transmittance measured with a spectrophotometer using the isolated coating film. The coating film was isolated by immersing the coated metal plate in an acid and dissolving the metal plate. In addition, the solar thermal reflectance R in the 0.8 to 2.1 μm wavelength region of the surface of each coating film on the plated steel sheet _{E / NIR} Was determined from the spectral reflectance measured with a spectrophotometer. Table 1 also shows the measurement results.
[0081]
On the other hand, as a pigment to be contained in the coating film on the back side of the painted metal plate,
(5) White titanium oxide pigment Taipe CR-90 (manufactured by Ishihara Sangyo, average particle diameter 0.4 μm) (symbol “TI”), and
(6) Scale-like aluminum powder 0700M [made by Toyo Aluminum] (symbol “AL”)
Was used.
[0082]
In the case of the white pigment (5), 40 parts by weight of this pigment, 60 parts by weight of a polyester resin as a binder, and 10 parts by weight of a melamine-based cross-linking agent are mixed and dispersed and mixed together with an appropriate amount of a solvent of cyclohexanone using a ball mill. And a paint was prepared. This paint was applied to various substrates by a roll coating method so as to have a dry film thickness of 5 μm, and baked at 240 ° C. for 60 seconds to form a white paint film on the back surface side.
[0083]
The flaky aluminum powder (6) was mixed with 5 parts by weight, 100 parts by weight of a polyester resin as a binder, and 10 parts by weight of a melamine-based crosslinking agent, and dispersed and mixed together with an appropriate amount of a solvent, cyclohexanone, using a ball mill. And a paint was prepared. This paint is applied to various substrates by a roll coating method so that the content of aluminum powder (aluminum pigment) becomes the amount shown in Table 1, and baked at 240 ° C. for 60 seconds to obtain a metallic color on the back side. Was formed.
[0084]
Table 1 shows the composition of the coating film on the substrate, the solar radiation surface and the back surface of the obtained coated metal plate.
With respect to the back side of this coated metal plate, the spectral reflectance in the wavelength region of 4.5 to 25 μm was measured, and the relative temperature when the absolute temperature was 293 K in Planck's thermal radiation spectrum distribution specified in JIS R3106. The emissivity of the back surface was determined from the value. This value is also shown in Table 1.
[0085]
A sample having a length of 150 mm and a width of 200 mm was cut out from the above coated metal plate and, as shown in FIG. The effect of the sample on the temperature rise inside the thermal insulation container after exposure to water was investigated.
[0086]
The heat retaining container 6 shown in FIG. 1 is configured such that the side walls other than the opening have good heat insulation properties, the sample is attached to the opening, and the surface of the sample is irradiated with sunlight at the same angle outdoors. It is arranged on a device (not shown) that follows the solar radiation. A thermocouple 4 is installed inside the heat retaining container 6, and the thermocouple 4 is connected to a recorder 5 provided outside so that a temperature change inside the heat retaining container 6 can be measured. Table 1 shows the measured maximum temperatures.
[0087]
[Table 1]

As can be seen from Table 1, in the coated metal plate of the present invention example in which the reflective pigment was contained in the outer layer of the coating film on the solar radiation side, the inside of the heat retaining container 6 was higher than the comparative example in which the pigment was not solar reflective. The temperature reached a maximum of about 10 ° C. or lower, indicating good solar heat reflectivity. Among them, the solar heat transmittance T of the coating film _{E / NIR} Is as high as 25%, and the solar thermal reflectance R of the substrate is _{E / NIR} Was as high as 73%, showing the best performance.
[0088]
The amount of the pigment added to the coating film on the back side is 40 parts by weight for titanium oxide (TI) and 5 parts by weight for the scale-like aluminum pigment (AL), and the latter is much smaller. Therefore, the emissivity of the back surface of Samples 8 and 9 having a very small amount of attached AL is lower than that of Samples 1 to 7, but the attached amount of this AL pigment is 0.05 g / m ² Above, the emissivity was 70% or less. 1.2 g / m of AL pigment ² , The emissivity was very low at 10%, even though the amount of the pigment attached was still smaller than that of TI.
[0089]
(Example 2)
In this example, the binder resin of the solar heat reflective coating was changed based on the coated metal plate shown as Test No. 7 (Example of the present invention) or Test No. 2 (Comparative Example) in Table 1 in Example 1, And / or a stain resistant coating was formed thereon to investigate stain resistance. The test materials produced in this example are as follows.
[0090]
(1) The same coating as in Test No. 7 except that the amount of the polar group in the polyester resin of the binder was adjusted to form a solar heat reflective coating film having a contact angle to water of 55 °, 65 ° or 85 °. A coated metal plate comprising a film and a substrate was produced. Test Nos. 11 to 13
(The contact angles are 55, 65 and 85 ° in order).
[0091]
(2) A coated metal plate comprising a coating film and a substrate was prepared in the same manner as in Test No. 7 except that a fluororesin was used instead of the polyester resin as the organic resin for the binder (Test No. 14). The contact angle of this coating film surface with water was 95 °.
[0092]
(3) A polyester resin paint capable of forming a film having a contact angle to water of 55 ° is applied on the solar heat reflective coating film obtained in Test No. 7 so as to have a dry film thickness of 3 μm, and dried. A clear coating film was formed (Test No. 15).
[0093]
(4) On the solar heat reflective coating obtained in Test No. 7, apply a fluororesin paint so as to have a dry film thickness of 3 μm, and dry to form a clear coating having a water contact angle of 95 °. Formed (Test No. 16).
[0094]
(5) The same coating film and substrate as in Test No. 2 except that the amount of polar groups in the polyester resin of the binder was adjusted to form a solar heat reflective coating film having a water contact angle of 55 ° or 65 °. Was prepared. These are designated as test numbers 17 and 18.
[0095]
After exposing the test material of the coated metal plate of the above test numbers 11 to 18 at an angle of 45 ° from a horizontal plane and exposing it outdoors for 3 months, without removing the surface dirt, the exposed surface is placed on the upper surface Then, as shown in FIG. 1, it was attached to the upper surface of the heat insulating container 6 and exposed to sunlight outdoors to measure the temperature rise in the container as described in Example 1. Table 2 shows the maximum temperature together with the reflectance of the coated metal plate.
[0096]
[Table 2]

As can be seen from Table 2, the coated metal plates of Test Nos. 11 to 16 based on Test No. 7 of the present invention were the same as those of Test No. 7 regardless of the contact angle of the surface with water. In addition, the solar heat reflection was high, the temperature rise in the heat insulation container was low, and the heat insulation was excellent. On the other hand, the coated metal plate based on Test No. 2 which is a comparative example had low solar heat reflection properties and poor heat shielding properties as in Test No. 2. That is, the change of the binder resin for imparting the stain resistance or the overcoating of the clear coating does not significantly affect the solar heat reflectivity.
[0097]
Regarding the stain resistance, in Test Nos. 11, 14, 15, 16 and 17 in which the contact angle of water on the surface is 60 ° or less or 90 ° or more, the basic test number 7 in Table 1 (test number in Table 2) was used. 11 to 16) or Test No. 2 (for Test Nos. 17 to 18 in Table 2). It can be seen that there was little adhesion, and the solar heat reflectivity was reduced, and thus the heat shield property was reduced. On the other hand, in Test Nos. 12, 13, and 18 in which the contact angle was 65 ° or 85 °, it was found that the heat-shielding property after outdoor exposure was significantly reduced, and the stain resistance was inferior to that described above.
[0098]
【The invention's effect】
The coated metal sheet having high solar heat reflectivity of the present invention is mainly suitable as an exterior material for building materials such as roofs, and is excellent in lightness and heat shielding properties required for roofs, can be colored in any color, and has high productivity. Can be manufactured well at low cost. In addition, by imparting contamination resistance to the solar radiation surface, a decrease in solar heat reflectivity due to contamination can be suppressed, and heat insulation is maintained for a long time.
[Brief description of the drawings]
FIG. 1 is a sectional view of an apparatus for measuring the reflectivity of a surface-treated metal plate.
[Explanation of symbols]
1: sunlight, 2: reflective layer, 3: substrate, 4: thermocouple,
5: Recorder, 6: Insulated container

Claims (9)

A coated metal plate obtained by applying a coating to a metal substrate and having a solar heat reflectance (RE _{/ NIR} ) of 20% or more in a wavelength region of 0.8 to 2.1 μm of the surface receiving the solar radiation and a surface receiving the solar radiation. A solar heat-reflective painted metal plate, characterized in that the emissivity of the opposite surface is 70% or less. The outer layer coating of opposite surface is 0.05 to 1.5 g / m ² containing flake aluminum pigment according to claim 1 coated metal sheet according. At least one layer of a solar reflective coating containing 2-70% by mass of a pigment having a solar thermal reflectance (RE _{/ NIR} ) of 10% or more in a wavelength region of 0.8 to 2.1 μm was provided on the surface receiving sunlight. The coated metal sheet according to claim 1 or 2. The solar heat reflectance (R _{E / NIR} ) in the wavelength region of 0.8 to 2.1 μm of the surface of the metal substrate which receives the solar radiation is 40% or more, and the solar heat transmittance in the wavelength region of 0.8 to 2.1 μm ( The coated metal sheet according to any one of claims 1 to 3, which has a pigment-containing coating film having a _{TE / NIR} ) of 20% or more. The coated metal plate according to claim 4, wherein the metal substrate is a plated metal plate having a plating film containing 50% by mass or more of aluminum. The coated metal sheet comprises two or more coating films, at least the outer coating film is the solar reflective coating film, and the coating thickness on the inner side is 200 μm or less. Painted metal plate. The coated metal sheet according to any one of claims 1 to 6, wherein a contact angle of the surface receiving the solar radiation with water is 60 ° or less or 90 ° or more. The coated metal sheet according to any one of claims 3 to 7, wherein a surface of the surface receiving the sun is formed of a solar heat reflective coating film, and a contact angle of the coating film with water is 60 ° or less or 90 ° or more. The coated metal sheet according to any one of claims 3 to 7, further comprising a coating having a contact angle to water of 60 ° or less or 90 ° or more and a thickness of 0.5 to 50 µm on the solar heat reflective coating.

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